The scientific cooperation of the Boreskov Institute of Catalysis with the catalytic communities from various countries is effected in accordance with various forms of cooperation: conducting joint seminars on catalysis, exchanging the information and appropriate materials, exchanging research fellows, visiting scientific centers, and participating in congresses and symposia on theoretical and applied catalysis.
According to research programs, projects and grants, the fundamentals of catalysis are studied jointly with researchers from various universities, institutions, research laboratories and companies. BIC collaborates fruitfully on a commercial basis with the leading companies from more than 20 countries, sells licenses, know-how and performs research projects according to client requests.
Academician Valentin N. Parmon is the Russian representative in the European Federation of Catalytic Societies (EFCATS), Member of the International Association of the Catalysis Societies (IACS)
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A QUANTUM CHEMICAL STUDY OF THE MOLECULAR STRUCTURE OF ACTIVE CENTERS AND GROWTH IN ETHYLENE POLYMERIZATION IN THE CATALYTIC SYSTEM LFeCl2/AlMe3 (L = 2,6-BIS-IMINOPYRIDYL)
I.I. Zakharov, V.A. Zakharov
Kinet. Catal., 45(4) (2004) pp. 508-518.
Density functional theory with hybrid exchangecorrelation functional B3P86 is used to calculate the molecular structures of neutral Fe(II) complexes formed in the LFeCl2/AlMe3 system (L=tridentate bis(imine)pyridyl ligand). A simplified model of the LFeCl2complex is used in calculations, where L is replaced by three NH3 ligands. Parameters of geometric and electronic structures of the complexes (NH3)3FeMe(μ -Me)AlMe3 (I) and (NH3)3FeMe(μ -Me)2AlMe2 (IIA and IIB), which are the structures where the Fe–Me and Fe-μ -Me groups are in one or two perpendicular planes, respectively, were determined. Complexes II, which were earlier identified using 1H NMR spectroscopy, are more stable than complex I. Complex IIB is strongly polarized (the distances r(Fe- μ-Me) and r(Al- μ-Me) are 3.70 and 2.08 Å, respectively) and coordinatively unsaturated due to the transfer of the methyl group from (NH3)3FeMe2 onto AlMe3. It has significant electron density deficit in the coordination sphere of the transition metal [(NH3)3FeMe]Q (Q = +0.80 e). The energetic profile of the reaction of ethylene addition to the Fe–Me bond for the complexes (NH3)3FeMe2, IIA and IIB, was calculated. It was shown that, compared to (NH3)3FeMe2, a drastic decrease in the activation energy of ethylene addition is observed in the case of IIB (from 135 to 66 kJ/mol). The reason for the more efficient activation of the complexes LFeMe2 by a weak Lewis acid (AlMe3) and for the increased reactivity of the metal-alkyl bond in complex IIB compared to the zirconocene complex Cp2ZrMe2 is discussed.
A DFT QUANTUM-CHEMICAL STUDY OF THE STRUCTURE OF PRECURSORS AND ACTIVE SITES OF CATALYST BASED ON 2,6-BIS(IMINO)PYRIDYL Fe(II) COMPLEXES
I.I. Zakharov, V.A. Zakharov
Macromol. Theory Simul., 13(7) (2004) pp. 583-591.
A DFT method has been applied for quantumchemical calculations of the molecular structure of charge-neutral complex LFeMe(μMe)2AlMe2 which is formed in system LFeMe2+AlMe3 (L=2,6-bis(imino)pyridyl). Calculations suggested the formation of highly polarized complex LFeMe(μMe)2AlMe2 (II) in system LFeMe2+AlMe3, characterized by r(Fe⎯μMe) = 3.70 Å and r(Al-μMe) = 2.08 Å and deficient electron density on fragment [LFeMe]Q (Q = +0.80 e). Polarization of the complex progresses with the bounding of two AlMe3 molecules (complex LFeMe(μMe)2AlMe2 2AlMe3 (III)) and with replacement of AlMe3 by MeAlCl2 (complex LFeMe(μMe)2AlCl2 (IV)). The activation energy of ethylene insertion into the FeMe bond of these complexes has been calculated. It was found that the heat of π-complex formation increases with increasing of polarization extent in the order II < III < IV. Activation energy of the insertion of coordinated ethylene into Fe-Me bond decreases in the same order: II > III > IV.
QUANTUM–CHEMICAL CALCULATIONS OF THE EFFECT OF CYCLOALIPHATIC GROUPS IN α-DIIMINE AND BIS(IMINO)PYRIDINE ETHYLENE POLYMERIZATION PRECATALYSTS ON THEIR STABILITIES WITH RESPECT TO DEACTIVATION REACTIONS
S.S. Ivanchev, A.V. Yakimansky*, D.G. Rogozin (*Institute of Macromolecular Compounds, St. Petersburg, Russia)
Polymer, 45 (2004) pp. 6453-6459.
For the first time, it is attempted to interpret an experimentally found enhancing effect of cycloaliphatic substituents in aromatic rings of NiII– and PdII-α-diimine and FeII–bis(imino)pyridine ethylene polymerization precatalysts on their catalytic activities at elevated temperatures (60-80°C), using quantum chemical Density Functional Theory calculations of relative stabilities of the complexes with respect to different deactivation processes, including thermal decomposition and one-electron reduction. It was shown that the effect correlates with the calculated higher thermal stabilities of cycloalkylsubstituted FeII-, NiII- and PdII-complexes as compared to the corresponding alkyl-substituted ones. NiII- and PdII-α-diimine complexes with cycloalkyl substituents are shown to be more stable than their alkylsubstituted analogues with respect to both thermal decomposition and one-electron reduction. The averaged difference of the thermal decomposition energies between the complexes with cycloaliphatic substituents on one side and aliphatic ones on the other side is ∼2.3 kcal/mol, corresponding to ∼30 times lower equilibrium constant of the thermal decomposition reaction for the cycloalkyl-containing complexes. For the FeII- and PdII-complexes, the thermal stability correlates with the calculated overlap population of the metal-nitrogen bonds. It was shown that the structure of o-substituents (cycloalkyls vs. alkyls) in the phenyl rings of the ligands does not affect the reaction energies for the transformation reactions of the precatalysts into their corresponding active cationic forms.
COPPER HYDROXIDE CATALYSTS FOR SELECTIVE OXIDATION: QUANTUM CHEMICAL STUDY OF ACTIVE SITES
A.S. Kosheleva, I.V. Yudanov, G.M. Zhidomirov, V.N. Parmon
React. Kinet. Catal. Lett., 82(2) (2004) pp. 347-354.
The Cluster models of the copper hydroxide structure were constructed to investigate the oxidation of organic substrates containing unsaturated C-C bonds in the Cu(OH)2/[Ncy]2[Ocy]2 catalytic system. The B3LYP density functional calculations of the activation barriers for ethylene epoxidation by the mono- and binuclear CuII hydroperoxo complexes corroborated the possibility of non-radical oxygen transfer from the terminal CuOOH hydroperoxo group. The activation barriers presented are relatively high compared to the barriers in the range of 12-15 kcal/mol calculated at the same computational level for TiIV hydroperoxo intermediates and ReVII bisperoxo complexes.
DENSITY FUNCTIONAL STUDY OF Pd NANOPARTICLES WITH SUBSURFACE IMPURITIES OF LIGHT ELEMENT ATOMS
I.V. Yudanov, K.M. Neyman*, N. Rösch* (*Technische Universität Munchen, Germany)
Phys. Chem. Chem. Phys., 6(1) (2004) pp. 116-123.
Atomic H, C, N and O at the surface and in the subsurface region of Pd nanoparticles were studied theoretically using an all-electron scalar relativistic density functional approach. Nanosize metal clusters are modelled by the three-dimensional crystallites Pd79 and Pd116 chosen as octahedral fragments of bulk Pd; these clusters expose (111) and (001) facets. Adsorbed atoms were located at the three-fold hollow sites in the centre of (111) facets. Migration of the atoms from the surface of the cluster Pd79 to the octahedral subsurface (oss) site below was considered. Migration of C from the surface hollow site to the oss position was found to be almost isoenergetic; migration of H is somewhat endothermic (by 0.5 eV). For N and O, a lager endothermicity was calculated. Both H and C species exhibit moderate activation barriers for the diffusion to the oss site. C and O atoms in the tetrahedral subsurface (tss) position of the cluster Pd116 were also studied. For both species, this location is energetically disfavoured, although the endothermic effect of O atom migration to the tss position is ~0.5 eV smaller than to the oss site. Subsurface C impurities were calculated to reduce the adsorption energy of CO molecules at Pd clusters.
DFT CLUSTER MODELING OF MOLECULAR AND DISSOCIATIVE HYDROGEN ADSORPTION ON Zn2+ IONS WITH DISTANT PLACING OF ALUMINUM IN THE FRAMEWORK OF HIGH-SILICA ZEOLITES
A.A. Shubin, G.M. Zhidomirov, V.B. Kazansky*, R.A. van Santen** (*Zelinsky Institute of Organic Chemistry, Moscow, Russia; **Schuit Institute of Catalysis, Eindhoven University of Technology, Eindhoven, The Netherlands)
Catal. Lett., 90(3-4) (2003) pp. 137-142.
The problem of various cationic positions in zeolites with high Si/Al ratio in the framework is discussed. The statistical distribution of Al in the lattice of pentasils makes probable appearance of the structures with distant placing of two Al atoms. Cations, localized at such sites, should be very strong Lewis acids that are highly active in different chemical reactions. An example of such site is considered for two Zn2+ ions stabilized in the zeolite fragment represented by two adjacent 5-membered rings sharing the common edge. DFT calculations of molecular and dissociative hydrogen adsorption by such sites are in agreement with experimental results. Adsorption of dihydrogen by zinc ion at such sites results in unusually large low frequency shift of H-H stretching vibrations indicating essential activation of adsorbed H2 molecule. The calculated path of heterolytic dissociative adsorption of dihydrogen and of the proton migration to the distantly placed basic oxygen of such acid-base pair are in agreement with the previously published DRIFT experimental data.
MODELS OF FINELY DISPERSED MgO AND V2O5 ON SILICA. THEORETICAL ANALYSIS OF OPTICAL PROPERTIES BY TD DFT METHOD
V.I. Avdeev, G.M. Zhidomirov
Res. Chem. Intermed., 30(1) (2004) pp. 41-64.
Calculations of the optical properties of vanadium (V) complexes VOCl3, [VOCl4]1-, [VOCl5]2-, and [VO4]3- ion have been performed in the frames of the density functional theory (DFT). Full spectrum of excited states in the region of 25000-60000 cm-1 has been analyzed by the time-dependent DFT method (TDDFT). Spectroscopy of structure defects – low-coordinated (LC) oxygen ions, and surface point defects – F+ and F sites in MgO has been studied in the cluster approximation. The charge transfer spectra and frequencies of normal vibrations for a number of active site models of finely dispersed oxides MgO and V2O5 on silica have been calculated. Comparison of obtained results with experimental electronic diffuse reflectance spectra and fundamental frequencies confirms a hypothesis about the structure of active centers of finely dispersed oxide V2O5 on silica as monomeric forms, (O=V-On).
MOLECULAR MECHANISM OF ETHYLENE EPOXIDATION ON SILVER: STATE OF THE PROBLEM AND THEORETICAL APPROACHES
G.M. Zhidomirov, V.I. Avdeev, A.I. Boronin
In “Computer Material Science”, Eds. C.R.A. Catlow, E. Kotomin, NATO Sci. Ser. III, IOS Press, Amsterdam, Vol. 187, 2003, pp. 334-358.
A new concept of the oxygen species epoxidizing ethylene on silver is presented. The epoxidizing oxygen is formed on the defects of the partially oxidized metal silver surface. Oxygen saturates the bulk of silver at high temperature (T>500 K) and pressure of the reaction medium, and the whole subsurface layer becomes highly defective. A cluster model of the defect structure surface ASV, including a silver atom vacancy and the subsurface oxygen atoms is considered. Calculations were performed in the framework of DFT approach. It was shown that the subsurface oxygen atoms tend towards self-association and formation of quasi-molecular oxygen structures inside of the vacancy space. Adsorption of the oxygen atom on site ASV also provides stabilization of the surface quasi-molecular (“ozonide”) form, ASV + O → ASd-O. The experimental XPS, UPS, IR, and Raman spectroscopy providing evidence in favor of stabilization of the quasi-molecular oxygen forms on the reactive silver surface is discussed. A theoretical interpretation of the experimental data is based on the proposed model of associative oxygen forms.
QUANTUM-CHEMICAL STUDY OF CnF2n+2 CONFORMERS. STRUCTURE AND IR SPECTRA
L.N. Ignatieva*, A.Yu. Beloliptsev*, S.G. Kozlova**, V.M. Buznik (*Institute of Chemistry, Vladivostok, Russia; **Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia)
J. Struct. Chem., 45(4) (2004) pp. 599-609.
Quantum-chemical calculations of the geometrical structure and vibrational spectra of CnF2n+2 oligomers (n = 5–8) in the chain and branched conformations are reported. The lengthening of the chain of CnF2n+2 does not substantially affect the geometrical parameters of the oligomers. In all cases under study, the most optimal structure of the molecule is a zigzag chain with bond lengths R(C-C) = 1.53–1.54 Å and R(C-F) = 1.36–1.34 Å; the chain is rolled into a helix, which makes an angle of 17° with the plane. The IR spectra are sensitive to the structural deficiency of oligomers CnF2n+2 associated with the lateral trifluoromethyl groups formed in the chain; the spectra can be used for revealing defects of this type in the structure of polytetrafluoroethylene (PTFE). The possibility of defects associated with the lateral CF3 groups in the structure of PTFE and its lowtemperature modifications is explained based on the calculated total energies of CnF2n+2.
STRUCTURE OF MODIFIED POLYTETRAFLUOROETHYLENE ACCORDING TO DFT CALCULATIONS AND 19F NMR SPECTROSCOPY
V.M. Buznik, S.P. Gabuda*, S.G. Kozlova*, A.K. Tsvetnikov** (*Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia; **Institute of Chemistry, Vladivostok, Russia)
J. Struct. Chem., 44(6) (2003) pp. 1152-1155.
The molecular structure of n-C7F16 and the 19F nuclear magnetic screening tensors are calculated by density functional theory (DFT) methods. The results of calculations are compared with 19F NMR data, and it is shown that fine polytetrafluoroethylene (PTFE) contains the terminal CF3 groups in its structure.
MODELING THE GAS-PHASE REDUCTION OF NITROBENZENE TO NITROSOBENZENE BY IRON MONOXIDE: A DENSITY FUNCTIONAL THEORY STUDY
I.L. Zilberberg, M. Ilchenko*, O. Isayev**, L. Gorb**, J. Leszczynski** (*Institute of Cell Biology and Genetic Engineering, Kiev, Ukraine; **Computational Center for Molecular Structure and Interaction, Department of Chemistry, Jackson State University, Jackson, Mississippi)
J. Phys. Chem. A, 108(22) (2004) pp. 4878-4886.
The gas-phase selective reduction of nitrobenzene (NB) to nitrosobenzene (NSB) by iron monoxide has been for the first time studied by means of density functional theory (DFT) using both the hybrid and pure exchange-correlation functionals. As shown at both DFT levels, when interacting with NB, the iron center donates an electron into the nitro group to form the NB- anion radical strongly coupled by FeO+. This electron-transfer characteristic of the NB--FeO+ intermediate reveals itself in the S2 operator expectation value that exceeds its eigenvalue of S(S+1) by almost 1.0. Further reaction steps necessary to obtain nitrosobenzene from this intermediate are discussed. One of the possible steps based on the abstraction of oxygen from the nitro group by a ferrous center is considered in detail. This reaction appears to be favorable at the pure DFT level, whereas the hybrid theory predicts small endothermicity for the process.
POSSIBLE MOLECULAR STRUCTURE OF PROMOTED LEWIS ACIDITY SITES IN ZnZSM-5
G.M. Zhidomirov, A.A. Shubin, V.B. Kazansky*, R.A. van Santen** (*Zelinsky Institute of Organic Chemistry, Moscow, Russia; **Schuit Institute of Catalysis, Eindhoven University of Technology, Eindhoven, The Netherlands)
Int. J. Quant. Chem., 100(4) 2004) pp. 489-494.
It is suggested that the abnormal methane IR frequency shift observed in ZnZSM-5 zeolites is caused by adsorptive interaction of CH4 with particularly strong Zn2+ Lewis sites. Various molecular structures of zinc ion species in high-silica zeolites are discussed and it is concluded that increased Lewis acidity of a sites is associated with their decreased structural stability. It is shown that Zn2+ in zeolite cationic position with distantly placed Al ions can produce observed shift of vibrational frequencies for adsorbed methane molecule.
COMPUTATIONAL STUDY OF BENZENE TO PHENOL OXIDATION CATALYZED BY N2O ON IRON EXCHANGED FERRIERITE
N.A. Kachurovskaya*, G.M. Zhidomirov, R.A. van Santen* (*Schuit Institute of Catalysis, Eindhoven University of Technology, Eindhoven, The Netherlands)
J. Phys. Chem. B, 108(19) (2004) pp. 5944-5950.
An Fe(II) ion at an α-cation exchange position of ferrierite, (Fe)α was taken as a model for the active site in nitrous oxide decomposition and in the selective oxidation of phenol with nitrous oxide. The oxygen deposited by decomposition of N2O is commonly referred to as α-oxygen, (O)α. Comparison with the results of cluster model calculations was performed for reaction of benzene to phenol oxidation. Periodic calculations predict the same reaction path for benzene oxidation like cluster model study. Differences in the adsorption modes for both types of calculations were analyzed and discussed.
COMPARATIVE ENERGIES OF Zn(II) CATION LOCALIZATION AS A FUNCTION OF THE DISTANCE BETWEEN TWO FORMING CATION POSITION ALUMINIUM IONS IN HIGH-SILICA ZEOLITES
N.A. Kachurovskaya*, G.M. Zhidomirov, R.A. van Santen* (*Schuit Institute of Catalysis, Eindhoven University of Technology, Eindhoven, The Netherlands)
Res. Chem. Intermed., 30(1) (2004) 99-103.
Periodical calculations of Zn(II) metal cation stabilization in cationic positions with distantly placed aluminium ions has been performed for high-silica ferrierite. It was found that decrease of the stabilization energy at large distances between Al ions (more than 10 Å ) is about of 2 eV in comparison with nearest possible position of two Al ions in the zeolite lattice and weekly depended on following increase of the Al---Al distance. Main changes in stabilization energy occurred within 3 Å interval of these distances. Only for the localizations of both Al ions in one zeolite ring zinc cationic form is more stable than hydrogen form.
CLOSED AND OPEN-SHELL ATOMIC OXYGEN ON SILVER: TWO DISTINCT PATTERNS OF THE O1S BINDING ENERGY AND X-RAY ABSORPTION O K-EDGE SPECTRA AS REVEALED BY DENSITY FUNCTIONAL THEORY
S.Ph. Ruzankin, I.L. Zilberberg, G.M. Zhidomirov
Res. Chem. Intermed., 30(1) (2004) pp. 75–85.
The electronic structure of atomic oxygen adsorbed species is studied by means of the density functional theory in the context of the ethylene epoxidation on the silver surface. The adsorbed oxygen species are modeled by the Ag2O molecule either in its closed (1A1) or open-shell states (3B1 and 1B1 ). In both open-shell states the 1s level appears to be lower than that in 1A1 by about 2 eV. This is apparently a sequence of the separation of electron pair, occupying the π*-type highest occupied molecular orbital (HOMO), decreasing the electron density at the oxygen center. Such variation of the O1s level for closed and open-shell Ag2O states seems to explain the X-ray photoelectron spectroscopy (XPS) data concerning two distinct atomic oxygen species on silver surface having the O1s binding energy of about 528 and 530 eV, called nucleophilic and electrophilic oxygen, respectively. The X-ray absorption O K-edge spectra (XANES) calculated for two types of the Ag2O states by means of multiple-scattered-Xα-based approach appears to be in a qualitative agreement with those experimentally recorded for nucleophilic and electrophilic oxygen.
EXPANSION OF THE UNRESTRICTED DETERMINANT IN THE BASIS OF PAIRED ORBITALS
I.L. Zilberberg, S.Ph. Ruzankin
Chem. Phys. Lett., 394(1-3) (2004) pp. 165-170.
An analysis of spin mixture contained in the unrestricted determinant using Löwdin–Amos-Hall paired orbitals (POs) is developed. The space of POs is divided into subspaces of completely, partially and non-overlapping orbitals. Spin contamination is shown to be associated with the ‘active’ space of 2k partially overlapping POs with k being in practice fairly small number. In the basis of POs the unrestricted determinant is expanded in a linear combination of restricted determinants describing ‘basis’ configurations contained 0,1, . . . , k pairs of spatially separated α and β spins.
UNRESTRICTED DENSITY FUNCTIONAL THEORY OF THE BONDING BETWEEN NO RADICAL AND FERROUS ION
I.L. Zilberberg, S.Ph. Ruzankin, S.E. Malykhin, G.M. Zhidomirov
Chem. Phys. Lett., 394(4-6) (2004) pp. 392–396.
Bonding between NO and the Fe(II) center to form so-called FeNO7 unit has been studied using simplistic Fe(NO)(OH)2 system within the unrestricted density functional theory using hybrid and pure exchange-correlation functionals. To analyze in details the obtained unrestricted solution for ground state with Sz = 3/2 corresponding Kohn–Sham determinant is expanded in the basis of Löwdin–Amos–Hall paired orbitals. This expansion allowed to assign the electron structure of FeNO7 unit as a mixture of charge-transfer configurations Fe+ ··· NO+ and Fe3+ ··· NO-, and the covalent configuration Fe2+ = NO0.
A COMPARATIVE, TWO-DIMENSIONAL 14N ESEEM CHARACTERIZATION OF REDUCED [2Fe-2S] CLUSTERS IN HYPERTHERMOPHILIC ARCHAEAL HIGHAND LOW-POTENTIAL RIESKE-TYPE PROTEINS
S.A. Dikanov*, A.A. Shubin, A. Kounosu**, T. Iwasaki**, R.I. Samoilova*** (*Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, USA; **Department of Biochemistry and Molecular Biology, Nippon Medical School, Tokyo, Japan; ***Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia)
J. Biol. Inorg. Chem., 9(6) (2004) pp. 753-767.
It is reported here the comparative orientationselected ESEEM and HYSCORE studies of the reduced clusters from two hyperthermophilic Riesketype proteins; a high-potential, archaeal Rieske protein called sulredoxin (SDX) from Sulfolobus tokodaii with weak homology to the cytochrome bc-associated Rieske proteins, and a low-potential, archaeal homolog of an oxygenase-associated Rieske-type ferredoxin (ARF) from Sulfolobus solfataricus. 14N ESEEM and HYSCORE spectra of SDX and ARF show well-defined variations, which are primarily determined by changes of quadrupole couplings (up to 50% depending on the selected orientation) of the two coordinated nitrogens. These are due to variations in coordination geometry of the histidine imidazole ligands rather than to variations of hyperfine couplings of these nitrogens, which do not exceed 8–10%. The measured quadrupole couplings and their differences in the two proteins are consistent with those calculated using the reported crystal structures of high- and low-potential Rieske proteins. These results suggest that exploration of quadrupole tensors might provide a more accurate method for characterization of the histidine coordination in different proteins and mutants than hyperfine tensors, and might have potential applications in a wider range of biological systems.
THE INFLUENCE OF TEMPERATURE AND PRESSURE ON HYDROGEN ATOM TRANSFER IN TUNNEL SOLID-PHASE REACTIONS
L.I. Trakhtenberg*, A.A. Fokeev*, V.L. Klochikhin*, S.P. Dolin**, B.N. Plakhutin (*Karpov Institute of Physical Chemistry, Moscow, Russia; **Kurnakov Institute of General and Inorganic Chemistry, Moscow, Russia)
Chem. Phys., 23(6) (2004) pp. 56-68.
Dependencies of the rate constant of a solid-phase tunnel reaction on temperature and pressure are considered. The T-dependence is determined by intermolecular and mild intramolecular vibrations in the reactants that cause oscillations in the permeability of the potential barrier for the tunneling atom. The influence of the external pressure is accounted for by a static decrease in the width and height of the potential barrier. The role of various promoting vibrations and T- and P-dependencies in the “acridine-fluorene” system are estimated using quantum chemical calculations of parameters of the reaction system. Anomalous values are discovered before and after annihilation of the first trace constituent of the UHF function in the “acridine-fluorene” system.
CATALYTIC PROCESSES OVER SUPPORTED NANOPARTICLES: SIMULATION
V.I. Elokhin, A.V. Myshlyavtsev* (*Omsk State Technical University, Omsk, Russia)
In “Dekker Encyclopedia of Nanoscience and Nanotechnology”, Eds. J.A. Schwarz, C.I. Contescu, K. Putyera, Marsel Dekker, Inc., New York, 2004, pp. 621-632.
In heterogeneous catalysis, adsorption and reaction processes usually occur on supported metal nanoparticles. To study such processes experimentally, a vast variety of surface-science techniques came into the use in the last decades of the 20th century. Along with the appearance of highprecision techniques for surface characterisation, considerable progress in manufacturing of model catalysts with well-defined properties like particle size, shape and separation has been achieved. Despite this progress, the cognitive potential of the experimental studies in this field is still limited because the measurements are usually indirect and the information derived demands quantitative processing and interpretation. This can be done only with the use of mathematical models. Successful interpretation of the results requires constructing mathematical models providing accurate description of systems under consideration. Application of the conventional meanfield models is often limited here due to the peculiarities of the reaction performance on the nm scale, including the inherent heterogeneity of metal crystallites as well as spontaneous and adsorbateinduced changes of the shape and degree of dispersion of supported catalysts. Under such circumstances, the use of stochastic simulations based, e.g., on the Monte Carlo technique, is almost inevitable. This entry is focused on theoretical studies (simulation) of the catalytic reaction kinetics on the active supported nanoparticles. The goal of this contribution is to describe the main achievements of the corresponding theoretical works.
PERIODIC PERTURBATION OF THE KINETICS OF HETEROGENEOUS CATALYTIC REACTIONS
V.P. Zhdanov
Surf. Sci. Rep., 55(1) (2004) pp. 1-48.
Periodic forcing of reaction kinetics via, e.g., variation of reactant pressure(s), temperature or flow reversal is one of the useful tools employed in basic and applied studies of heterogeneous catalytic processes. In the case of conventional (stable) kinetics, this strategy is used to clarify the mechanisms of reactions and obtain data on reaction rate constants or to improve the reaction performance, e.g., to increase reaction rate and/or selectivity with respect to desired products. In experiments, that are focused on oscillatory catalytic reactions, periodic perturbations are employed to stabilize period-1 oscillations. This is easily achieved if the external and internal frequencies are equal. In a more general context, periodic perturbation of chemical reactions, that exhibit period-1 oscillations, may result in complex reaction behaviour, including period doubling and irregular kinetics provided that the external and internal frequencies do not coincide. In this review are considered both the relevant data available in the literature and the results of systematic calculations for a few generic models.
SIMULATION OF THE GROWTH AND DIFFERENTIATION OF STEM CELLS ON A HETEROGENEOUS SCAFFOLD
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Phys. Chem. Chem. Phys., 6(17) (2004) pp. 4347-4350.
Monte Carlo simulations illustrating that scaffolds with specially designed heterogeneities can be used as a tool for governing the growth and differentiation of stem cells are presented. This tool is predicted to be efficient provided that the size of the heterogeneities exceeds (but not appreciably) the cellular size and the rate of cell diffusion is relatively fast compared to that of cell division.
FROM A PLURIPOTENT STEM CELL TO AN ENSEMBLE OF DIFFERENTIATED CELLS: ELEMENTS OF THEORETICAL TISSUE ENGINEERING
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Phys. Chem. Chem. Phys., 6(1) (2004) pp. 138-143.
Monte Carlo lattice simulations are presented illustrating how the growth of stem and differentiated cells on a uniform surface can be governed (guided differentiation) by tuning long-range cell-cell communication. Due to spatial constraints on cell division, the growth rate is shown to strongly depend on the interplay of cellular division, diffusion, and signaling. With decreasing diffusion rate, the kinetics become slower. To increase the selectivity of the growth with respect to "desirable'' cells, one can use induced messenger-mediated generation of these cells by stem cells. The simplest schemes based on this idea may, however, result in appreciable slowdown of the growth. A more optimal strategy may be simultaneous promotion of generation of desirable cells and stem cells.
ROLE OF THE FIELD FLUCTUATIONS IN ELECTROCHEMICAL REACTIONS
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Appl. Surf. Sci., 219(3-4) (2003) pp. 256-263.
Rate constants of electrochemical reactions, accompanying by electron transfer via the electrolytemetal interface, exponentially depend on the electrode potential. Monte Carlo simulations are presented illustrating the effect of fluctuations of the potential near the reactants on the rate of such reactions. The two models employed are based on the phenomenological Frumkin theory and aimed, respectively, at conventional electrolytes and polymer electrolytes widely used in fuel cells. In both cases, the role of spatio-temporal fluctuations is found to be minor if the dielectric constant in the double layer is large, similar or equal to 80 (as in the bulk water). If the double-layer dielectric constant is smaller, e.g. similar or equal to 30 as it often takes place in conventional and polymer electrolytes, the fluctuations result in appreciable increase of the apparent reaction rate constant. This effect is especially important (of a factor of 15) for polymer electrolytes. In the latter case, the reaction rate is actually controlled by the fluctuations. Implications of these findings for basic and applied electrochemistry are briefly discussed.
TOWARDS THE UNDERSTANDING OF THE SPECIFICS OF REACTIONS IN POLYMER ELECTROLYTE FUEL CELLS
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Surf. Sci., 554(2-3) (2004) pp. 103-108.
In low-temperature hydrogen-oxygen polymerelectrolyte fuel cells, catalytic reactions usually occur on nm-sized Pt particles located on the walls of a porous carbon support. The electrolyte is usually a hydrated polymer (e.g., NAF-ION), which consists of hydrophobic chains and hydrophilic subchains and contain appreciable amount of water (up to about 40%). The heterogeneity of the electrolyte has the same length scale (about 10 nm) as the size of catalyst particles. To elucidate some specific aspects of reactions occurring under these conditions, Monte Carlo lattice simulations are presented illustrating probable distributions of polymer and water near Pt particles. In the case of cathodic processes, the Pt surface is predicted to be free of polymer, the double layer near Pt to be uniform, and the role of polymer in the surface electrochemistry to be minor. During anodic processes, the polymer chains seem to directly participate in formation of the double layer near Pt, the field distribution in the double layer is far from uniform, and accordingly the role of polymer in surface electrochemistry is appreciable.
INFLUENCE OF ELECTROLYTE ON ELECTRON DIFFUSION IN MESOPOROUS NANOCRYSTALLINE TiO2
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
J. Phys.: Condens. Matter, 16(15) (2004) pp. 2625-2629.
Experimental studies show that the rate of electron diffusion in mesoporous nanocrystalline TiO2 may depend on the electrolyte concentration. In the available literature, this effect is attributed to ambipolar diffusion. The arguments and a kinetic model are presented indicating that it might instead be connected with different arrangements of cations near the traps occupied by an electron before and after tunnelling. With a reasonable choice of the ratio of the kinetic parameters, in agreement with experiment, the model predicts that the electron diffusion coefficient at high electrolyte concentrations may be about five times higher than at low concentrations.
ONE OF THE SCENARIOS OF ELECTROCHEMICAL OXIDATION OF CO ON SINGLE-CRYSTAL Pt SURFACES
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Surf. Sci., 545(1-2) (2003) 109-121.
Monte Carlo simulations are presented illustrating that the transient potential-step kinetics of CO oxidation on single-crystal Pt surfaces are fairly sensitive to adsorbate-adsorbate lateral interactions. Specifically, it is shown that with realistic values of these interactions (similar or equal to 1 kcal/mol) the reaction kinetics may be accompanied by CO segregation provided that surface CO diffusion is fast. In addition, it is demonstrated that the CO-island formation may be one of the reasons of extinction in CO oxidation. Implications of these findings for interpretation of experimental data are discussed.
THE EFFECT OF OXIDE FORMATION ON BISTABILITY IN CO OXIDATION ON Pt
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
J. Catal., 220(2) (2003) pp. 478-485.
Kinetics of CO oxidation on Pt is bistable both under UHV conditions and at atmospheric pressure. In the former case, the bistability can be explained by using the established reaction scheme, including reversible CO adsorption, dissociative O2 adsorption, and reaction between adsorbed CO and O. Also at higher pressures, this model accounts well for the lowreactive (CO-dominated) regime. However, in the high-reactive (oxygen-rich) regime, the kinetics may be influenced by surface oxide formation at the higher pressures. The present Monte Carlo simulations illustrate what may happen when oxide formation and removal occur with participation of gas-phase O2 and CO molecules, respectively. Specifically, it is shown that these relatively slow steps may control the reaction rate in the high-reactive state. In this case, the hysteresis loop is found to be qualitatively similar to that predicted by the conventional reaction scheme, but the CO2 formation rate in this state is appreciably lower. These predictions are in qualitative agreement with the results of recent STM studies of CO oxidation on Pt(110) at atmospheric pressure.
COMMENT ON “HYSTERESIS PHENOMENA IN CO CATALYTIC OXIDATION SYSTEM IN THE PRESENCE OF INHOMOGENEITIES OF THE CATALYST SURFACE”
V.P. Zhdanov
Phys. Rev. E, 68 (2003) 068101 (2 pp).
Scrutinizing the Monte Carlo algorithm, used by D.-Y. Hua and Y.-Q. Ma [Phys. Rev. E, 66, 066103 (2002)] in order to simulate the effect of defect sites on bistable kinetics of CO oxidation on single-crystal surfaces, it is shown that in their study (i) the rules for describing CO adsorption, desorption, and surface diffusion contradict the detailed balance principle and (ii) the ratio of the rates of CO diffusion and reaction between adsorbed CO and O species is opposite compared to that observed in reality.
KINETIC OSCILLATIONS ON nm-SIZED CATALYST PARTICLES: NO REDUCTION BY CO ON Pt
V.P. Zhdanov
Catal. Lett., 93(3-4) (2004) pp. 135-138.
Monte Carlo simulations of kinetic oscillations in the NO-CO reaction occurring due to the interplay of catalytic steps including autocatalytic NO dissociation are presented. The lattice size is varied from 100x100 to 10x10 in order to mimic nm-sized catalyst particles. More or less regular oscillations are found for the sizes down to 15x15. In combination with similar results obtained earlier for two other models describing CO oxidation accompanied by oxide formation and surface restructuring, this finding forms one of first firm quantitative ingredients of the theory of oscillatory kinetics on supported catalysts.
COMMENT ON “MODELLING PATTERN FORMATION IN CO+O2 REACTION ON Pt(100)”
V.P. Zhdanov
Chem. Phys. Lett., 390(1-3) (2004) pp. 301-304.
I.M. Irurzun. R.B. Hoyle, M.R.E. Proctor and D.A. King [Chem. Phys. Lett., 377 (2003) 269] have recently proposed a novel coarse-grained approach to describing the transport of adsorbed CO molecules along the quasi-hexagonal and (1 x 1) patches during kinetic oscillations in CO oxidation on the Pt(100) surface. Analysis indicates that this approach cannot be used as a robust tool for analysing the pattern formation in oscillatory catalytic reactions, because it contradicts the basic principles of general theory of mass transport.
PERTURBATION OF PERIOD-2 OSCILLATIONS IN CATALYTIC REACTIONS ACCOMPANIED BY SURFACE RESTRUCTURING
V.P. Zhdanov
Phys. Rev. E, 68 (2003) 056212 (6 pp.).
Monte Carlo simulations illustrating the effect of periodic forcing on period-2 oscillations related to the interplay of catalytic reaction and surface restructuring are presented. The oscillations are found to be fairly stable if the external frequency equals the main internal frequency. In contrast, perturbations with other frequencies may easily change the type of oscillation. In particular, perturbations with double frequency convert period-2 oscillations into period-1 oscillations with the imposed frequency.
BIFURCATION IN A GENERIC MODEL OF INTRACELLULAR VIRAL KINETICS
V.P. Zhdanov
J. Phys. A: Math. Gen., 37(5) (2004) L63-L66.
The key steps of intracellular virion reproduction include viral genome replication, mRNA synthesis and degradation, protein synthesis and degradation, capsid assembly and virion release from a cell. The analysis, incorporating these steps (with no deterioration of the cell machinery), indicates that asymptotically depending on the values of the model parameters the viral kinetics either reach a steady state or are out of control due to an exponential growth of the virion population. In the latter case, the cell is expected to rapidly die or the virion growth should be limited by other steps.
KINETICS OF PROTEIN AGGREGATION WITH FORMATION OF UNREACTIVE INTERMEDIATES
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Langmuir, 20(7) (2004) pp. 2543-2545.
Irreversible protein aggregation resulting in formation and deposition of insoluble fibrils or amorphous precipitates is usually assumed to occur via sequential attachment of monomers to soluble intermediates. This scheme is complemented by slow conversion of the intermediates to a relatively stable form so that they do not react with monomers but can be trapped by precipitates. For reasonable values of parameters, our model predicts that the aggregation kinetics order may be between 2.0 and 2.5. In particular, the model can be used to explain the reaction order, 2.17 +/- 0.09, observed for aggregation of recombinant human granulocyte colony stimulating factor.
PROPAGATION OF INFECTION AND THE PREY-PREDATOR INTERPLAY
V.P. Zhdanov
J. Theor. Biol., 225(4) (2003) pp. 489-492.
The article contains Monte Carlo simulations illustrating propagation of infection and the preypredator interplay.
NANOMETER-SIZED ANTENNA FOR ENHANCEMENT OF ABSORPTION OF LIGHT BY DYE MOLECULES
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Göteborg, Sweden)
Appl. Phys. Lett., 84(10) (2004) pp. 1748-1749.
One of the ways to increase the absorbance of dye molecules is to optimize the property of their environment. In particular, a dye molecule can be surrounded by a few other molecules absorbing at lower frequencies. Analysis indicates that the amplification factor of such nanometer-sized antennas may be up to about 200.
PROPYLENE OXIDATION BY PALLADIUM NITRO AND NITRATO COMPLEXES: IN SITU NMR AND IR STUDIES
I.E. Beck, A.V. Golovin, V.A. Likholobov, E.V. Gusevskaya* (*Departamento de Quı́mica- ICEx, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brésil)
J. Organometal. Chem., 689(18) (2004) pp. 2880-2887.
The mechanism of the propylene oxidation by Pd(NOn)Cl2−m(CH3CN)2 complexes (n = 2, 3; m = 0, 1, 2) in chloroform solutions has been studied by 1H NMR and IR spectroscopy. The main reaction products are acetone and 2-nitropropylene, with their ratio depending on the equilibrium existing in the reaction solutions between palladium complexes containing NOn ligands bonded to a palladium atom via either an oxygen or a nitrogen atom. Reactivities of the oxygen bonded nitrato and nitrito complexes are significantly higher than that of the nitrogen bonded nitro complex. Various new organopalladium intermediates have been observed and monitored in situ. A reversible insertion of the coordinated propylene into the Pd–O or Pd–N bonds results in nitrato-, nitrito- and nitropalladation intermediates, which then decompose via a β-hydrogen elimination. Two isomers of the nitritopalladation intermediate have been detected, i.e., a palladium metallacycle and an open ring complex, with the latter being much more reactive towards the β-hydrogen elimination than the former. The decomposition of the nitrato- and nitritopalladation intermediates results in the organometallic precursor of acetone, i.e., an acetonylpalladium complex, and then in acetone itself. On the other hand, the nitropalladation intermediate originates 2-nitropropylene. In the presence of dioxygen, which re-oxidizes the nitrosyl groups, the acetone formation becomes a catalytic reaction with respect to both palladium and nitrogen.
CO DISSOCIATION AND CO HYDROGENATION ON SMOOTH AND ION-BOMBARDED Pd(111): SFG AND XPS SPECTROSCOPY AT MBAR PRESSURES
G. Rupprechter*, V.V. Kaichev, H. Unterhalt*, M. Morkel*, V.I. Bukhtiyarov (*Fritz-Haber-Institut der MPG, Berlin, Germany)
Appl. Surf. Sci., 235(1-2) (2004) pp. 26-31.
The CO dissociation probability on transition metals is often invoked to explain the product distribution (selectivity) of catalytic CO hydrogenation. Along these lines, CO adsorption and dissociation on smooth and ion-bombarded Pd(111) at pressures up to 1 mbar were investigated using vibrational sum frequency generation (SFG) and X-ray photoelectron spectroscopy (XPS). Under high pressure, CO adsorbate structures were observed that were identical to high-coverage structures in UHV. On ion-bombarded surfaces an additional species was detected which was attributed to CO bridge bonded to defect (low-coordinated) sites. On both surfaces, no indications of CO dissociation were found even after hours of 0.1 mbar CO exposure. However, exposing CO/H2 mixtures to ion-bombarded Pd(111) produced carbonaceous deposits suggesting CHxO species as precursors for C---O bond cleavage and that the formation of CHxO is facilitated by surface defects. The relevance of the observations for CO hydrogenation on Pd catalysts is discussed.
C--O BOND SCISSION ON “DEFECT-RICH AND PERFECT” Pd(111)?
V.V. Kaichev, M. Morkel*, H. Unterhalt*, I.P. Prosvirin, V.I. Bukhtiyarov, G. Rupprechter*, H.J. Freund* (*Fritz-Haber- Institut der MPG, Berlin, Germany)
Surf. Sci., 566-568(Part 2) (2004) pp. 1024-1029.
To investigate the influence of surface defects on CO adsorption and dissociation, well-annealed and "defect-rich" Pd(111) were examined by sum frequency generation (SFG) and X-ray photoelectron spectroscopy (XPS) within the pressure range 10−6–1 mbar. Ar+ ion sputtering was employed to produce surface defects which exhibited vibrational and photoemission characteristics different from the regular adsorption sites on Pd(111). Even under highpressure, SFG and XPS indicated that no CO dissociation occurred on both surfaces at 300–400 K. By contrast, C–O bond scission was observed during methanol decomposition producing carbonaceous deposits beside CO and H2. A possible relationship between the adsorption geometry and C–O bond scission is discussed.
METHANOL DEHYDROGENATION AND FORMATION OF CARBONACEOUS OVERLAYERS ON Pd(111) STUDIED BY HIGH-PRESSURE SFG AND XPS SPECTROSCOPY
M. Morkel*, V.V. Kaichev, G. Rupprechter*, H.J. Freund*, I.P. Prosvirin, V.I. Bukhtiyarov (*Fritz-Haber-Institut der MPG, Berlin, Germany)
J. Phys. Chem. B, 108(34) (2004) pp. 12955-12961.
Methanol decomposition on Pd(111) at 300 and 400 K was studied in situ from 5×10-7 to 0.1 mbar by combining vibrational sum frequency generation (SFG) and X-ray photoelectron spectroscopy (XPS). Two competing decomposition pathways, i.e., dehydrogenation of CH3OH to CO and H2 and methanolic C-O bond scission, were observed by monitoring the time-dependent evolution of CO/CHxO and of carbonaceous deposits CHx (x=0-3) via their vibrational and photoemission characteristics. Quantification of carbon-containing species was performed by XPS, while the preferred binding site of CHx was determined by SFG using CO as probe molecule for postreaction adsorption. In contrast to previous reports, Pd(111) was found to be quite active for methanolic C-O bond scission. The CHx formation rate strongly increased with pressure and temperature, leading to immediate catalyst deactivation at 0.1 mbar and 400 K. The combined SFG/XPS data suggest that the carbonaceous residues are highly dehydrogenated, such as CH or carbon atoms bonded to hollow sites. Complete dehydrogenation of CHx species and partial dissolution of atomic carbon in the Pd bulk most likely occurred even at 300 K. On the other hand, the CHx species was found to be unexpectedly thermally stable (up to ~600 K), until carbon dissolution and formation of carbon clusters take place. Regeneration with oxygen above 400 K was able to remove CHx deposits and to partially restore the initial adsorption properties. Corresponding experiments with CO did not produce any carbon signals, indicating that the cleavage of the C-O bond must occur via CHxO intermediates (and not within CO). Methanol decomposition at pressures up to 15 mbar and temperatures up to 550 K, followed by gas chromatography, did not produce measurable decomposition products, due to fast carbon poisoning under catalytic reaction conditions.
METHANOL OXIDATION ON A COPPER CATALYST INVESTIGATED USING IN SITU X-RAY PHOTOELECTRON SPECTROSCOPY
H. Bluhm*, M. Hävecker*, A. Knop-Gericke*, E. Kleimenov*, R. Schlögl*, D. Teschner**, V.I. Bukhtiyarov, D.F. Ogletree***, M. Salmeron*** (*Fritz-Haber-Institut der MPG, Berlin, Germany; **Institute of Isotope & Surface Chemistry, Budapest, Hungary; ***Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California)
J. Phys. Chem. B, 108(38) (2004) pp. 14340-14347.
The surface and near-surface regions of an active catalyst and the adjacent gas-phase reactants were investigated simultaneously under reaction conditions using in situ X-ray photoelectron spectroscopy (XPS). This investigation of methanol oxidation on a copper catalyst showed that there was a linear correlation between the catalytic activity of the sample and the presence of a subsurface oxygen species that can only be observed in situ. The concentration profile of the subsurface oxygen species within the first few nanometers below the surface was determined using photon-energy-dependent depthprofiling. The chemical composition of the surface and the near-surface regions varied strongly with the oxygen-tomethanol ratio in the reactant stream. The experiments show that the pure metal is not an active catalyst for the methanol oxidation reaction, but that a certain amount of oxygen has to be present in the subsurface region to activate the catalytic reaction. Oxide formation was found to be detrimental to formaldehyde production. Our results demonstrate also that for an understanding of heterogeneous catalysts a characterization of the surface alone may not be sufficient, and that subsurface characterization is essential.
CO ADSORPTION ON Au(110)-(1 x 2): AN IRAS INVESTIGATION
D.C. Meier*, V.I. Bukhtiyarov, D.W. Goodman* (*Department of Chemistry, Texas A&M University, Texas)
J. Phys. Chem. B, 107(46) (2003) pp. 12668-12671.
IRAS studies of CO adsorption on the Au(110)-(1×2) surface were performed as a function of CO pressure and sample temperature. It was found that with increasing coverage, the CO IRAS absorption shifts red from 2118 to 2108 cm-1. Clausius-Clapeyron data analysis yielded a heat of CO adsorption (-Hads) of 10.9 kcal/mol at low coverages and 7.8 kcal/mol at coverages greater than 19%.
APPLICATION OF NMR MICROIMAGING TO STUDY MASS TRANSFER AND CHEMICAL REACTIONS
I.V. Koptyug*, A.A. Lysova, A.V. Matveev, R.Z. Sagdeev*, V.N. Parmon (*International Tomography Centre, Novosibirsk, Russia)
Catal. Ind., Special issue (2004) pp. 60-67.
A possibility of application of NMR-Microimaging to study a wide class of masstransfer processes in model reactors, granular layers, and porous granules, including that under the conditions of a catalytic reaction, has been demonstrated and systematically investigated. Direct visualization of liquid and gas flows in the channels of different geometry was carried out. Distribution of molecules on rates of movement in a layer were obtained for the processes of filtration of liquids, gases, and solid particles in granular layers and the coefficients of longitudinal and transverse dispersion were measured. Multiphase catalytic processes proceeding in an isolated grain of the catalyst were investigated by NMR-imaging on the examples of reactions of hydrogen peroxide decomposition and α-methylstyrene hydrogenation.
FUNCTIONAL IMAGING AND NMR SPECTROSCOPY OF AN OPERATING GAS-LIQUID-SOLID CATALYTIC REACTOR
I.V. Koptyug*, A.A. Lysova, A.V. Kulikov, V.A. Kirillov, V.N. Parmon, R.Z. Sagdeev* (*International Tomography Centre, Novosibirsk, Russia)
Appl. Catal. A, 267(1-2) (2004) pp. 143-148.
This work reports the first application of nuclear magnetic resonance (NMR) imaging to study the behaviour of a gas–liquid–solid model catalytic reactor operating at elevated temperatures. Two techniques from the magnetic resonance imaging (MRI) toolkit, namely functional MRI and NMR spectroscopic imaging, have been employed to perform a dynamic in situ study of α-methylstyrene catalytic hydrogenation on a single catalyst pellet or in a granular bed. Owing to reaction exothermicity, a reciprocating motion of the liquid front within the pellet accompanied by pellet temperature oscillations has been observed even when the external conditions were kept unchanged. Spatially resolved information on the reactant to product conversion within the catalyst bed has been obtained for a steady-state regime. The results represent a first direct MRI visualisation of the mutual influence of mass and heat transport processes and a chemical reaction in an operating reactor and demonstrate that NMR imaging and spectroscopy techniques can be used successfully to study the development of critical phenomena in operating multiphase reactors. It is suggested that further development of the applications of the MRI toolkit in chemical and process engineering and catalysis hold significant promise for the development of safe and efficient technologies based on a detailed understanding of the interplay of various processes in an operating gas–liquid–solid reactor.
MÖSSBAUER STUDIES OF THE PHASE COMPOSITION AND MICROSTRUCTURE OF THE La1-xCaxFeO3-y SYSTEM AS RELATED TO THE REACTIVITY OF SURFACE AND BULK OXYGEN
L.A. Isupova, I.S. Yakovleva, I.I. Gainutdinov*, Yu.T. Pavlyukhin*, V.A. Sadykov (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia)
React. Kinet. Catal. Lett., 81(2) (2004) pp. 373-382.
The phase composition and microstructure of samples of the La1-xCaxFeO3-y system prepared via a ceramic route were characterized by Mössbauer spectroscopy. In all cases, iron was found in the 3+ state. The ordering of anion vacancies in the samples with the composition in the range of 0.8 > x ≥0.4, which corresponds to a microheterogeneous solid solution, generates new distorted octahedral and fivefold/tetrahedral sites revealed by two typical sextets. The disordering of this solid solution and small (10-100 Å) sizes of domains with a perovskite, braunmillerite or Grenier phase structure caused the appearance of a superparamagnetic doublet, which grows with the Ca content up to x = 0.8 but disappears in the sample of pure braunmillerite. The appearance of Fe cations in a distorted coordination correlates with the increased activity of the samples with a microheterogeneous structure in the CO catalytic oxidation and with their reducibility by H2.
OXYGEN STATES IN OXIDES WITH A PEROVSKITE STRUCTURE AND THEIR CATALYTIC ACTIVITY IN COMPLETE OXIDATION REACTIONS: SYSTEM La1-xCaxFeO3-y (x = 0–1)
L.A. Isupova, I.S. Yakovleva, V.A. Rogov, G.M. Alikina, V.A. Sadykov
Kinet. Catal., 45(3) (2004) pp. 446-452.
Oxygen states in the La1-xCaxFeO3-y perovskites prepared using different procedures are studied by temperature-programmed reduction (TPR). Results are compared to data on the catalytic activity in the oxidation of methane and carbon monoxide. The activity of the samples in the CO and CH4 oxidation over a wide temperature range (200–600°C) is shown to correlate with the amount of reactive surface and subsurface oxygen removable during TPR below 420°C. These oxygen states in the samples of the La1-xCaxFeO3-y series can be associated with the domain or intergrain boundaries. No correlation is found between the amount of lattice oxygen removable during TPR and the activity of the La1-xCaxFeO3-y samples in the complete oxidation of methane at temperatures of 450–600°C. It is suggested that catalytic complete oxidation is determined by the most reactive surface and subsurface oxygen states located at the interphase boundaries, whereas the lattice oxygen does not participate in these reactions.
MOBILITY AND REACTIVITY OF THE SURFACE AND LATTICE OXYGEN OF SOME COMPLEX OXIDES WITH PERОVSKITE STRUCTURE
V.A. Sadykov, N.N. Bulgakov, V.S. Muzykantov, T.G. Kuznetsova, G.M. Alikina, A.I. Lukashevich, Yu.V. Potapova, V.A. Rogov, E.B. Burgina, V.I. Zaikovskii, E.M. Moroz, G.S. Litvak, I.S. Yakovleva, L.A. Isupova, V.V. Zyryanov, E. Kemnitz*, S. Neophytides** (*Institute of Chemistry, Humboldt-University, Berlin, Germany; **Institute of Chemical Engineering and High Temperature Chemical Processes, Patras, Greece)
In: “Mixed Ionic Electronic Conducting Perovskites for Advanced Energy Systems”, Eds. N. Orlovskaya, N. Browning, Kluwer Academic Publishers, Boston/Dordrecht/London, 2004, pp. 49-70.
Mobility and reactivity of the surface and bulk oxygen of perovskite-like mixed oxides including lanthanum manganite (I) and ferrite (II) systems modified by Ca (I,II) and fluorine (I), as well as some Co, Fe-containing complex perovskites known to be good mixed conductors were considered. Combination of thermal analysis data, dynamic and isothermal oxygen isotope exchange, O2 TPD, isothermal pulse/flow samples reduction by CO, H2 and CH4 TPR, was applied to characterize the accessible surface/bulk oxygen mobility and reactivity. Comparison of these results with earlier obtained data on the real (defect) structure of these systems by TEM, EXAFS, XRD, FTIRS of lattice modes, SIMS allowed to elucidate factors determining the oxygen mobility and reactivity. Quantitative description of the experimental energetic spectrum of oxygen bound with regular and defect surface sites of perovskites was obtained by using semiempirical Interacting Bonds method with a due regard for the surface faces termination and relaxation. Analysis of the barriers for oxygen migration in the perovskite lattice by this method revealed pronounced effect of cation vacancies.
MICROHETEROGENEOUS SOLID SOLUTIONS IN PEROVSKITES: FORMATION, MICROSTRUCTURE, AND CATALYTIC PROPERTIES
L.A. Isupova, S.V. Tsybulya, G.N. Kryukova, V.A. Rogov, I.S. Yakovleva, V.A. Sadykov
In: “Mixed Ionic Electronic Conducting Perovskites for Advanced Energy Systems”, Eds. N. Orlovskaya, N. Browning, Kluwer Academic Publishers, Boston/Dordrecht/London, 2004, pp. 143-162.
Influence of the point and extended defects on the steady-state catalytic activity of perovskites in deep oxidation processes is discussed.
THIOPHENE HYDRODESULFURIZATION ACTIVITY OF MoS2/Al2O3 CATALYSTS PREPARED VIA EXFOLIATION. THE EFFECT OF COBALT
D.I. Kochubey, V.A. Rogov, V.P. Babenko
React. Kinet. Catal. Lett., 83(1) (2004) pp. 181-186.
In contrast to the bulk MoS2, the structure of the active phase of the catalyst prepared via exfoliation is shown to exhibit a number of distortions, which form a superstructure of the type of the charge density waves with a quasi-period of 30 Å. Due to such distortions, the ions of cobalt firmly chemisorb on the basal plane of MoS2 occupying, along the perimeter of the MoS2 clusters, the regions with a lower energy of the Mo-S interaction. A synergetic increase in the catalyst activity due to the introduction of cobalt was observed up to the atomic ratios of Co/(Co+Mo) = 0.33, which is possible for the nanoparticles of MoS2 with a diameter 200 Å, only if cobalt adsorbs on the basal plane.
M.V. Luzgin, K. Thomas*, J. van Gestel*, J.-P. Gilson*, A.G. Stepanov (*Laboratoire Catalyse et Spectrochimie, CNRS - ENSICAEN – Université de Caen, Caen Cedex, France )
J. Catal., 223(2) (2004) pp. 290-295.
Using in situ 13C MAS NMR, it has been demonstrated that propane is carbonylated with carbon monoxide to produce isobutyraldehyde and isobutyric acid at 100-150°C on sulfated zirconia. Isobutyraldehyde represents the intermediate reaction product, almost completely converting into the acid at 150°C. Selective formation of isotyraldehyde indicates that the activation of propane by SZ is performed primarily toward secondary C-H bond rather than its C-C bond. This pathway of the alkane activation can be rationalized to occur either on the Lewis acid sites of SZ or by direct formylation by the formyl cation formed as equilibrated species from the formate. With the aid of IR spectroscopy the evidence was provided that the sulfate groups of SZ are accountable for the aldehyde oxidation, surface dithionate species being suggested to be formed as a result of sulfur reduction. The dithionate species are readily recovered to sulfate groups via oxidizing treatment in O2 atmosphere.
STUDIES OF THE MECHANISM OF AMMONIA OXIDATION INTO NITROUS OXIDE OVER Mn-Bi-O/α-Al2O3 CATALYST
E.M. Slavinskaya, S.A. Veniaminov, P. Notté*, A.S. Ivanova, A.I. Boronin, Yu.A. Chesalov, I.A. Polukhina, A.S. Noskov (*Solutia Europe, Louvain-la-Neuve, Belgium)
J. Catal., 222(1) (2004) pp. 129-142.
Complex of kinetic and physicochemical methods: temperature-programmed surface reaction (TPSR), pulsing NH3 or NH3/16O2 (18O2) reaction mixture, Infrared and Photoelectron Spectroscopies was used for characterization of the high selective supported manganese-bismuth oxide catalysts and for the studying of the mechanism of the ammonia oxidation. Ammonia oxidation was demonstrated to proceed via alternating reduction and reoxidation of the catalyst surface with participation of the lattice oxygen. NH3 interacts with weakly bonded oxygen species through hydrogen atom abstraction to form adsorbed [N] species, which are localized on Mn2+ and Mnδ (2<δ<3). Manganese ions with different oxidation degree (Mn3+ (Mn4+) and Mnδ+) serve as active sites of the catalyst surface. The correlation between the selectivity towards N2O and the portion of manganese in the Mn3+ (Mn4+) state was established. Bismuth oxide plays an important role in consequence of increasing of the quantity, mobility and thermal stability of the subsurface oxygen. The reaction kinetic scheme is suggested based on the experimental results. Numerical simulation of TPSR data confirms the reliability of the proposed reaction mechanism.
THE ROLE OF SUPPORT IN FORMATION OF THE MANGANESE-BISMUTH OXIDE CATALYST FOR SYNTHESIS OF NITROUS OXIDE THROUGH OXIDATION OF AMMONIA WITH OXYGEN
A.S. Ivanova, E.M. Slavinskaya, V.V. Mokrinskii, I.A. Polukhina, S.V. Tsybulya, I.P. Prosvirin, V.I. Bukhtiyarov, V.A. Rogov, V.I. Zaikovskii, A.S. Noskov
J. Catal., 221(1) (2003) pp. 213-224.
BET, XRD, XPS and TPR by hydrogen were used for investigation of supported Mn-Bi oxide catalysts for ammonia oxidation into nitrous oxide. The catalysts were synthesized by impregnation of γ−, α−Al2O3 and SiO2 with solutions of manganese and bismuth nitrates. The character of phase transformations, surface concentration and state of the active component were shown to depend on the nature of the support. The sequence stabilization of active constituents of the Mn-Bi-O/α-Al2O3 catalyst and types of the stabilized species were determined. The activity of the Mn-Bi-O supported catalysts calcined at 400°C was established to be equal 95–97% and to be practically independent of the support nature, while the activity decreased with elevation of the calcination temperature. The Mn-Bi-O/α-Al2O3 catalysts exhibited the highest selectivity to N2O (84.4%) under identical conditions. The correlation between the Mn3+/Mnδ+ (2<δ<3) ratio in the catalyst and the selectivity to N2O was revealed.
SELECTIVE OXIDATION OF AMMONIA OVER Ru(0001)
S.A.C. Carabineiro*, А.V. Matveev, V.V. Gorodetskii, B.E. Nieuwenhuys* (*Leiden University, Leiden Institute of Chemistry, Leiden, The Netherlands)
Surf. Sci., 555(1-3) (2004) pp. 83-93.
The decomposition and oxidation of NH3 have been studied on the Ru(0001) surface in the temperature range from 150 up to 800 K. The results were compared to those found for Ir(110) and Ir(510). TDS results showed that most of the ammonia is dissociatively adsorbed between 150 and 300 K, with formation of H2 around 300 K and N2 between 600 and 800 K. N2 desorption shifts to lower temperatures with increasing surface oxygen coverage. The products of ammonia oxidation observed were N2, H2O and N2O. Formation of NO was not found. Inhibition of the reaction presumably by N species was observed until 450 and 670 K, depending on the NH3/O2 ratios. Above those temperatures the reaction started as manifested by a decrease in the NH3 and O2 pressures and a simultaneous increase in the H2O, N2 and N2O pressures.
MECHANISM AND KINETICS OF THE SELECTIVE NO REDUCTION OVER Co-ZSM-5 STUDIED BY THE SSITKA TECHNIQUE. II. REACTIVITY OF NOX ADSORBED SPECIES WITH METHANE
E.M. Sadovskaya, A.P. Suknev, L.G. Pinaeva, V.B. Goncharov, B.S. Bal’zhinimaev, C. Chupin*, J. Pérez-Ramírez*, C. Mirodatos* (*Institut de Recherches sur la Catalyse, Villeurbanne Cedex, France)
J. Catal., 225 (2004) pp. 179-189.
Steady-state isotopic transient kinetic analysis (SSITKA) was applied to study the reactivity of adsorbed NOx species with methane over Co-ZSM-5 during CH4-SCR of NO at different partial oxygen concentrations. Numerical analysis of the isotope responses after switching from 14N16O to 15N18O, from 16O2 to 18O2, from 12CH4 to 13CH4, and from C16O2 to C18O2 in the feed gas was performed. This enables determination of (i) the concentration of surface intermediates resulting from the interaction of NOx species with methane. The NO reduction with CH4 in the presence of oxygen was shown to proceed by two different pathways with participation (1) NO2 δ+ species (formed on nanoclusters of cobalt oxide located inside the zeolite channels) and (2) NO2 - nitrite complexes (formed on larger cobalt oxide particles located outside the zeolite channels), the reaction rate by the former being appreciably higher under the SCR reaction condition studied. Mononitrosil species appear not be directly involved in the overall process. Modeling results indicate that the rate of the first route is limited by the interaction of NO2 δ+ species and adsorbed methane, while in the second route the formation of nitrite species is a ratedetermining step. Based on the obtained results, an overall reaction mechanism of the CH4-SCR of NO in the presence of oxygen is proposed.
REACTION KINETICS AND MECHANISM OF SELECTIVE NO REDUCTION ON A CoZSM-5 CATALYST AS STUDIED BY SSITKA
E.M. Sadovskaya, A.P. Suknev, V.B. Goncharov, B.S. Bal’zhinimaev, C. Mirodatos* (*Institut de Recherches sur la Catalyse, Villeurbanne Cedex, France)
Kinet. Catal., 45(3) (2004) pp. 436-445.
The dynamics of 13C transfer from methane to carbon dioxide was studied under the steady-state reaction conditions of selective NO reduction with methane on a CoZSM-5 catalyst at various reactant (NO, CH4, and O2) concentrations and temperatures. It was found that the reaction occurs by a two-pathway mechanism with the participation of Co2+ sites (or CoOx clusters) and paired Co2+–OH sites localized at the boundary between the clusters and the zeolite; in this case, the rate of the reaction at boundary sites was higher by more than one order of magnitude. Based on the numerical simulation of isotopic response curves, the concentrations of intermediate compounds and the rate constants of particular steps were evaluated; differences in the kinetics via the above reaction pathways were found and analyzed.
NO DECOMPOSITION OVER A NEW TYPE OF LOW METAL CONTENT FIBERGLASS CATALYSTS STUDIED BY TAP TECHNIQUE
A.P. Suknev, A.C. van Veen*, A.V. Toktarev, E.M. Sadovskaya, B.S. Bal’zhinimaev, C. Mirodatos* (*Institut de Recherches sur la Catalyse, Villeurbanne Cedex, France)
Catal. Commun., 5(11) (2004) pp. 691-695.
NO absorption and decomposition over novel type of leached fiberglass catalysts containing very small amounts of platinum were studied by means of the TAP technique. In the temperature range of 200-400°C NO was reversibly absorbed on the catalyst. At higher temperatures NO consumption and N2 release occurred, indicating the proceeding of direct NO decomposition. However, in the temperature range of 400-500°C the rate of NO decomposition declined with the quantity of NO dosed, i.e. with the number of pulses introduced, so that steady-state NO conversion was close to zero. This drop in catalyst activity is related to the negligible oxygen desorption during NO decomposition in this temperature range, making it reasonable to assume a blocking of the catalyst active sites by accumulating oxygen. Nevertheless, as temperature was raised above 500°C, steady-state NO conversion increased sharply with temperature reaching a value of 45 % at 550°C. Apparently, a thermal desorption of oxygen beyond that temperature allows to free sites, which were covered during NO decomposition, sustaining in this way the overall reaction. Based on the obtained data activation energies of NO desorption and decomposition were estimated.
HIGH SELECTIVE FIBER GLASS WOVEN CATALYSTS DOPED BY NOBLE METALS IN THE REACTIONS OF AROMATIC NITRO-COMPOUNDS REDUCTION
Ch. Wu*, V. Dorokhov*, A.P. Suknev, B.S. Bal’zhinimaev, V. Barelko* (*Institute of Problems of Chemical Physics, Chernogolovka, Russia)
Chem. Eng. Transac., 3 (2003) pp. 285-289.
The features of liquid-phase hydrogenation of trinitrotoluene and trinitrobenzene over woven silica fiberglass (SFG) catalysts doped by Pt (Pt content 0,1 wt.%) were investigated. Specific surface area (SSA) of the catalysts was ranged from 1 to 15 m2/g. The traditional Pd/C powdered catalyst (Pd content 5 wt.%, SSA of 500 m2/g) was used as reference sample. The SFG catalysts showed a higher specific activity than conventional Pd/C one. An unexpected finding for SFG catalysts was that hydrogenation rates of second and third nitro-groups in trinitrotoluene and trinitrobenzene were, respectively, by one and two orders of magnitude less than that of the first one. The selectivity effect was found to decrease with increasing of SSA for SFG catalysts and wasn’t revealed at all for Pd/C sample.
IN SITU FTIR STUDY OF PYRIDINE-3- CARBALDEHYDE ADSORPTION ON TiO2 (ANATASE) AND V-Ti-O CATALYST
G.Ya. Popova, Yu.A. Chesalov, T.V. Andrushkevich
React. Kinet. Catal. Lett., 83(2) (2004) pp. 353-360.
In situ FTIR spectroscopy was used to study the interaction of pyridine-3-carbaldehyde (3PyA) with the surface of ТiO2 and V-Ti-O catalyst in the temperature range of 120–300°C. 3PyA interacted with Lewis and Brønsted acid sites of ТiO2 and V-Ti-O catalyst to form nitrogen-coordinated complex and σ-bonded (through oxygen of CHO group) complex, as well as complex protonated at the N atom in the ring. Surface carboxylates (nicotinates) also were identified during interaction of 3PyA with the V-Ti-O catalyst at the temperature range of 200–300°C.
METHYLPYRAZINE AMMOXIDATION OVER BINARY OXIDE SYSTEMS. V. EFFECT OF PHOSPHORUS ADDITIVES ON THE PHYSICOCHEMICAL AND CATALYTIC PROPERTIES OF A VANADIUM-TITANIUM CATALYST IN METHYLPYRAZINE AMMOXIDATION
V.M. Bondareva, T.V. Andrushkevich, O.B. Lapina, D.F. Khabibulin, A.A. Vlasov, L.S. Dovlitova, E.B. Burgina
Kinet. Catal., 45(1) (2004) pp. 104-113.
Oxide vanadium–titanium catalysts modified by phosphorus additives (20V2O5–(80-n)TiO2–nР2O5, where n= 1, 3, 5, 10, and 15 wt %) are studied in methylpyrazine ammoxidation. Two regions of compositions are found corresponding to radically different catalytic properties, namely, catalysts with a low (≤ 5 wt % P2O5) and high (≥ 10 wt % P2O5) concentration of the additive. In the first case, the introduction of phosphorus is accompanied by a gradual increase in the activity. In the second case, an increase in the additive concentration results in a decrease in the activity and selectivity to the target product, pyrazineamide, and a simultaneous increase in the selectivities to by-products, pyrazine and carbon oxides. The catalysts are characterized by X-ray diffraction analysis, differential dissolution, IR, and NMR spectroscopic data. As in the binary system, the active sites of the samples with a low concentration of phosphorus contain V5+ cations in a strongly distorted octahedral oxygen environment, which are strongly bound to a support due to the formation of V–O–Ti bonds. The catalytic properties of the samples containing ≥ 10 wt % P2O5 are due to the presence of the phase of a triple V–P–Ti compound with an atomic ratio V : P : Ti approximately equal to 1 : 1 : 1. The V5+ cations in this compound occur in a weakly distorted tetrahedral oxygen environment and are bound to the tetrahedral P5+ cations.
THE STUDY OF NITRIC OXIDE ADSORPTION AND THE MECHANISM OF SURFACE “EXPLOSIONS” IN THE REACTION OF CO+NO ON Pt(100) AND Pd(110) SINGLE CRYSTAL SURFACES
A.V. Matveev, A.A. Sametova, V.V. Gorodetskii
Kinet. Catal., 45(4) (2004) pp. 598-606.
High resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) were used to study NO adsorption and the reactivity of COads and NOads molecules on Pd(110) and Pt(100) single crystal surfaces. Compared to the Pt(100)-(1×1) surface, the unreconstructed Pt(100)-hex surface is chemically inert toward NO dissociation into Nads and Oads atoms. When a mixed adsorbed COads + NOads layer is heated, a so-called surface “explosion” is observed when the reaction products (N2, CO2, and N2O) synchronously desorb in the form of sharp peaks with a half-width of 720 K. The shape specificity of TPR spectra suggests that the “vacancy” mechanism consists of the autocatalytic character of the reaction initiated by the formation an initial concentration of active sites due to partial desorption of molecules from the COads+NOads layer upon heating to high temperatures. Kinetic experiments carried out on the Pd(110) surface at a constant reaction pressure and a linear increase in the temperature confirm the explosive mechanism of the reaction NO+CO.
THE DETERMINATION OF INTERMEDIATE COMPOUNDS FORMED IN THE POLYCONDENSATION OF METHANOL IN THE GAS PHASE ON CHARGED MOLYBDENUM OXIDE CLUSTERS BY ION CYCLOTRON RESONANCE SPECTROMETRY
V.B. Goncharov
Russ. J. Phys. Chem., 78(12) (2004) pp. 1924-1928.
A set of oxygen-containing molybdenum clusters MoxOy (x = 1-3, y = 1-9) was obtained using a Knudsen cell in combination with an ion confinement cell. Reactions of positively charged clusters with methanol were studied by ion cyclotron resonance. Several organometallic ions resulting from the initial insertion of molybdenum oxide ions into the C–O and C–H methanol bonds and methanol polycondensation products were observed. The key intermediate that initiated the polycondensation of methanol was shown to be the Mo3O9CH3 + ion. The lower bond energy limits for MoxOy + complexes with the methyl radical were estimated to be D0(MoOy+-CH3) > 91.6 (y = 2, 3), D0(Mo2Oy +-CH3) > 91.6 (y = 4–6), and D0(Mo3O9 +-CH3) > 91.6 kcal/mol.
KINETICS OF THE OXIDATION OF β-PICOLINE TO NICOTINIC ACID OVER VANADIA-TITANIA CATALYST. II. THE NETWORK OF THE REACTION AND THE EFFECT OF WATER
E.V. Ovchinnikova, T.V. Andrushkevich, L.A. Shadrina
React. Kinet. Catal. Lett., 82(1) (2004) pp. 191-197.
Over vanadia-titania catalysts, the oxidation of β-picoline into nicotinic acid proceeds under a parallel-consecutive network. Nicotinic acid is formed both directly from picoline and through pyridine-3- carbaldehyde as an intermediate. Products of total oxidation and nitrile are formed on a parallel path from picoline, and on a consecutive path via overoxidation of partial oxidation products. Introduction of water into the reaction mixture raises selectivity and activity due to an acceleration of the formation of carbaldehyde and nicotinic acid and not due to repressing the reactions of total oxidation.
HYDRODECHLORINATION OF TETRACHLOROMETHANE IN THE VAPOR PHASE IN THE PRESENCE OF Pd-Fe/SIBUNIT CATALYSTS
E.V. Golubina*, E.S. Lokteva*, T.S. Lazareva*, B.G. Kostyuk*, V.V. Lunin*, V.I. Simagina, I.V. Stoyanova (*Moscow State Lomonosov University, Moscow, Russia)
Kinet. Catal., 45(2) (2004) pp. 183-188.
The hydrodechlorination of CCl4 in the presence of Pd–Fe/Sibunit catalysts of different composition was studied. An optimum concentration of the metals (2.5% at the ratio Pd/Fe = 1:4) was determined, which corresponds to the highest stability of catalysts and selectivity of C2–C4 olefin and paraffin formation. With the use of TPR and magnetic measurements, it was found that the metals occurred in an oxidized state in the course of the reaction; it is likely that this resulted in the formation of C2–C4 hydrocarbons.
MECHANISM OF THE LOW-TEMPERATURE INTERACTION OF HYDROGEN WITH α-OXYGEN ON FeZSM-5 ZEOLITE
K.A. Dubkov, E.V. Starokon’, E.A. Paukshtis, A.M. Volodin, G.I. Panov
Kinet. Catal., 45(2) (2004) pp. 202-208.
The mechanism of a low-temperature reaction of hydrogen with the radical anion surface oxygen species (α-oxygen, Oα) formed by decomposing N2O over FeZSM-5 zeolite was studied using kinetic and isotope techniques. It was found that the reaction is of first order with respect to hydrogen and the rate of the reaction is proportional to the concentration of Oα. The activation energy of the reaction, which was measured for H2 or D2 over a temperature range from +20 to -100ºC, is equal to 3.2 or 5.3 kcal/mol, respectively. The reaction occurs with a considerable kinetic isotope effect (kH/kD), which varies over the range of 3.4–41 depending on the temperature. This fact indicates that the rate-limiting step of the reaction includes the dissociation of the hydrogen molecule. The temperature dependence of the isotope effect gave a value of 2.1 kcal/mol, which is close to the difference between the zero bond energies in the molecules of H2 and D2; this fact suggests that a tunnel effect does not significantly contribute to the reaction. The dissociative mechanism is consistent with data obtained by in situ IR spectroscopy. The interaction of hydrogen with α-oxygen is accompanied by the formation of new hydroxyl groups OαH (absorption bands at 3635 and 3674 cm 1) at the surface of the zeolite. The identification of these groups was supported by an isotope shift either on the replacement of H2 by D2 or on the replacement of 16Oα by 18Oα. The stoichiometric ratio H2 : Oα is consistent with the previously drawn conclusion on the paired arrangement of α-sites.
LIQUID PHASE OXIDATION OF ALKENES WITH NITROUS OXIDE TO CARBONYL COMPOUNDS
E.V. Starokon’, K.A. Dubkov, D.E. Babushkin, V.N. Parmon, G.I. Panov
Adv. Synth. Catal., 346(2-3) (2004) pp. 268-274.
A variety of substrates including linear, cyclic, heterocyclic alkenes and their derivatives were tested in the liquid phase non-catalytic oxidation with nitrous oxide (N2O). The structure and composition of alkenes have significant effect on the reaction selectivity. With many alkenes, N2O oxidation provides a selective way for preparation of carbonyl compounds. Generation of carbene (or diazomethane) species is a remarkable feature of the oxidation of terminal alkenes.
METHANE OXIDATION IN A DIELECTRIC BARRIER DISCHARGE. THE IMPACT OF DISCHARGE POWER AND DISCHARGE GAP FILLING
A.A. Khassin, B.L. Pietruszka*, M. Heintze*, V.N. Parmon (*Institute of Low Temperature Plasma Physics, Greifswald, Germany)
React. Kinet. Catal. Lett., 82(1) (2004) pp. 111-119.
The conversion of an air-methane mixture in a dielectric barrier discharge (DBD) was studied in a wide range of temperatures and discharge powers for different gap fillings. The impact of the gap filling surface area appears to be negligible at temperatures below 530 K, while being significant above 570 K. Some processes on the surface are countercurrent to those in the DBD plasma.
THE IMPACT OF A DIELECTRIC BARRIER DISCHARGE ON THE CATALYTIC OXIDATION OF METHANE OVER Ni-CONTAINING CATALYST
A.A. Khassin, B.L. Pietruszka*, M. Heintze*, V.N. Parmon (*Institute of Low Temperature Plasma Physics, Greifswald, Germany)
React. Kinet. Catal. Lett., 82(1) (2004) pp. 131-137.
Methane oxidation with air was studied over a Ni-containing catalyst in a dielectric barrier discharge (DBD) at temperatures above 625 K. The DBD increases the methane conversion and shifts the process towards partial oxidation. This effect is related to a catalyst heating by the discharge.
A STUDY OF METHANE DECOMPOSITION OVER Ni-Si-CONTAINING CATALYSTS
A.A. Khassin, A.S. Kovalenko
Doklady Phys. Chem., 397(4-6) (2004) pp. 194-198.
The methane decomposition process over Ni-containing catalysts could be described by a scheme, which considers a gradual increase in the extent of the diffusion constrains (reaction rate control by kinetics → intraparticle diffusion control → deactivation → external kinetic regime) due to the accumulation of the filamentary carbon (FC) in the catalyst. The experimental values of the activation energy (190 ± 5 kJ/mol) and pre-exponential factor in the Arrhenius reaction rate equation (3.1013 s-1) over Ni/MgO reference sample indicate that the RDS of the methane decomposition process is the H–CHx bond cleavage. The Ni-Mg amesites showed low specific activity (30 time less than that for Ni/MgO) in the methane decomposition process and are therefore stable to coking in the methane decomposition reaction conditions.
COPRECIPITATED IRON-CONTAINING CATALYSTS (Fe-Al2O3, Fe-Co-Al2O3, Fe-Ni-Al2O3) FOR METHANE DECOMPOSITION AT MODERATE TEMPERATURES. I. GENESIS OF CALCINED AND REDUCED CATALYSTS
T.V. Reshetenko, L.B. Avdeeva, A.A. Khassin, G.N. Kustova, V.A. Ushakov, E.M. Moroz, A.N. Shmakov, V.V. Kriventsov, D.I. Kochubey, Yu.T. Pavlyukhin*, A.L. Chuvilin, Z.R. Ismagilov (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia)
Appl. Catal., A, 268(1-2) (2004) pp. 127-138.
Genesis of the composition and structure of the active component of coprecipitated iron containing catalysts (Fe-Al2O3, Fe-Co-Al2O3, Fe-Ni-Al2O3) with high metal loadings (>50 wt.%) for methane decomposition at moderate temperatures (600–650oC) has been investigated by XRD, EXAFS, radial electron density distribution (REDD), TEM, FTIR and Mössbauer spectroscopy. The main stages of the catalyst genesis during drying, thermal decomposition and reduction have been studied. For bimetallic systems (Fe-Co-Al2O3, Fe-Ni-Al2O3) intermediate spinel phases with a composition (M II, Fe)3O4 (M =Co, Ni) have been shown to form during heat treatment and reduction. This leads to a decrease of the reduction temperature for iron oxides. Reduced bimetallic catalysts (Fe-Co-Al2O3, Fe-Ni-Al2O3) are composed of alloys. The structure and parameters of their crystal lattices depend on the type and concentration of the added metal. Alumina has been shown to behave as a structural promoter. A model of the reduced catalysts consisting of highly dispersed (20–50 nm) metal and alumina particles with a spinel phase at their interface has been suggested.
COPRECIPITATED IRON-CONTAINING CATALYSTS (Fe-Al2O3, Fe-Co-Al2O3, Fe-Ni-Al2O3) FOR METHANE DECOMPOSITION AT MODERATE TEMPERATURES. II. EVOLUTION OF THE CATALYSTS IN REACTION
T.V. Reshetenko, L.B. Avdeeva, V.A. Ushakov, E.M. Moroz, A.N. Shmakov, V.V. Kriventsov, D.I. Kochubey, Yu.T. Pavlyukhin*, A.L. Chuvilin, Z.R. Ismagilov (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia)
Appl. Catal., A, 270(1-2) (2004) pp. 87-99.
Coprecipitated Fe-Al2O3, Fe-Co-Al2O3 and Fe-Ni-Al2O3 catalysts is shown to be very efficient in carbon deposition during methane decomposition at moderate temperatures (600–650oC). The carbon capacity of the most efficient bimetallic catalysts containing 50-65 wt.% Fe, 5–10 wt.% Co (or Ni) and 25–40 wt.% Al2O3 is found to reach 145 g/gcat. Most likely, their high efficiency is due to specific crystal structures of the metal particles and formation of optimum particle size distribution. According to the TEM data, catalytic filamentous carbon (CFC) is formed on them as multiwall carbon nanotubes (MWNTs). The phase composition of the catalysts during methane decomposition is studied using a complex of physicochemical methods (XRD, REDD, Mössbauer spectroscopy and EXAFS). Possible mechanisms of the catalyst deactivation are discussed.
A COMPARATIVE STUDY OF THE ACTIVITY OF OXIDE CATALYSTS IN THE OXIDATION OF METHANE AND 1,1-DIMETHYLHYDRAZINE
I.Z. Ismagilov, V.V. Kuznetsov, A.P. Nemudryi*, O.Yu. Podyacheva (*Institute of Solid-State Chemistry and Mechanochemistry, Novosibirsk, Russia)
Kinet. Catal., 45(5) (2004) pp. 722-729.
The catalytic oxidation of methane and 1,1-dimethylhydrazine ((CH3)2N-NH2, unsymmetrical dimethylhydrazine (UDMH)) with air on oxide catalysts was studied. Two pairs of perovskites (Ca0.7Sr0.3FeO2.5(3.0) and La0.7Sr0.3CoO2.5(3.0), stoichiometric and superstoichiometric with respect to oxygen) and a supported spinel (20%(CuxMg1–xCr2O4)/ν-Al2O3, IC-12-73) were used as catalysts. The experiments were performed using two laboratory flow-type systems: in a catalytic fixedbed reactor (the oxidation of CH4) and in a gradientless vibrationally fluidized bed reactor (the oxidation of CH4 and UDMH) at 150-700°C. In the oxidation of CH4, the IC-12-73 catalyst was more active than the perovskite catalysts, although particular perovskite catalysts can exhibit higher activity in the region of low temperatures. In the oxidation of UDMH, the activity of perovskites in the test temperature region was lower than that of IC-12-73; this correlates with the higher activity of IC-12-73 in the oxidation of CH4. The Ca0.7Sr0.3FeO3.0 and La0.7Sr0.3CoO2.5(3.0) perovskites exhibited similar activities in the deep oxidation of UDMH, which were higher than the activity of Ca0.7Sr0.3FeO2.5. A comparison between the selectivities of the conversion of fixed nitrogen, which is a constituent of UDMH, into nitrogen oxides SNOxN demonstrated that, on all of the perovskites, SNO N was higher and SN2O N was lower than the corresponding values on IC-12-73. Additional information on the possible mechanisms of intermediate formation in the adsorption and oxidation of UDMH on IC-12-73 was obtained using Fourier transform IR spectroscopy.
KINETICS OF THE MEDIUM-TEMPERATURE REDUCTION OF COPPER CHROMITE WITH HYDROGEN
I.I. Simentsova, A.V. Khasin, L.P. Davydova, T.M. Yurieva
React. Kinet. Catal. Lett., 82(2) (2004) pp. 355-361.
The static volumetric method was used to study the kinetics of copper chromite CuCr2O4 reduction with hydrogen at 50-80 kPa and 498, 523 and 580 K. The rate of copper chromite reduction is maximal initially and decreases monotonically with time. This observation suggests that the reduction is not a topochemical process. The apparent activation energy of the reaction equals initially 107 kJ/mole. The results obtained argue for a particular mechanism of the copper chromite reduction via redox substitution of hydrogen for copper in the chromite and, therefore, agree with earlier data obtained by various structural and adsorption methods. Specific features of the reduction mechanism are discussed.
IN SITU XRD AND HRTEM STUDIES ON THE EVOLUTION OF THE Cu/ZnO METHANOL SYNTHESIS CATALYST DURING ITS REDUCTION AND RE-OXIDATION
T.M. Yurieva, L.M. Plyasova, V.I. Zaikovskii, T.P. Minyukova, L.P. Davydova, I.Yu. Molina, M.P. Demeshkina, A.A. Khassin, A. Bliek*, J.C. van den Heuvel*, E.D. Batyrev* (*University of Amsterdam, Amsterdam, The Netherlands)
Phys. Chem. Chem. Phys., 6(18) (2004) pp. 4522-4526.
During the formation of the CuZnO solid solutions, the foreign anions in anion-modified (a.m.-) oxides give rise to: (i) extended stacking faults of (002) ZnO lattice plane, which are occupied by copper ions in the form of small clusters; and (ii) vacant inner holes of the a.m.-ZnO crystal. The main part of copper ions in the clusters is reduced to Cu0 with hydrogen at 473 K. According to HRTEM studies, the reduction of Cu0.08Zn0.92O results in the formation of copper metal species of two types: (i) particles of 3-10 nm in size on the a.m.-ZnO surface; and (ii) small (no more than 3 nm in size) atomic copper metal clusters in defect voids of the a.m.-ZnO structure. The copper metal clusters are coherent inclusions in the bulk of the ZnO, and the large copper metal particles are epitaxially bonded to the surface of the ZnO matrix. Copper metal particles on the surface of a.m.-ZnO are reoxidized to Cu+2 at 523 K in the helium flow containing 0.05 vol% oxygen, and they come back to the extended stacking faults. The copper metal clusters in the holes of a.m.-ZnO are inaccessible to the oxygen and are not reoxidized.
ACTIVE PHASES OF SUPPORTED COBALT CATALYSTS FOR 2,3-DIHYDROFURAN SYNTHESIS
L. Leite*, V. Stonkus*, K. Edolfa*, L. Ilieva**, D. Andreeva**, L.M. Plyasova, J.W. Sobczak***, S. Ionescu****, G. Munteanu**** (*Latvian Institute of Organic Synthesis, Riga, Latvia; **Institute of Catalysis, Bulgarian Academy of Sciences, Sofija, Bulgaria; ***Institute of Physical Chemistry, Polish Academy of Sciences, Warszawa, Poland; ****Romanian Academy Institute of Physical Chemistry “I.G. Murgulescu”, Bucharest, Romania)
J. Mol. Catal. A: Chem., 215(1-2) (2004) pp. 95-101.
Dehydrogenation of 1,4-butanediol to 2,3-dihydrofuran over kaolin-supported Co and Co–Au catalysts has been investigated. Catalytic test and XRD analysis show that the presence of metallic cobalt with hexagonal structure is favourable for selectivity to 2,3-dihydrofuran of the reaction studied. It was established by XPS method that an optimal for the reaction selectivity Co0/Co2+ ratio in Co/kaolin and Co–Au/kaolin catalysts exists. Quantum chemical calculations suggest that the initial step of 1,4-butanediol dehydrogenation on cobalt catalyst surface may be the cleavage of O---H bond to form alkoxide species on Co2+ ion. Based on the effect of metallic and ionic cobalt on the catalyst selectivity, it could be presumed that both cobalt species are involved in the rate-determining step in dehydrogenation of 1,4-butanediol into 4-hydroxybutanal intermediate.
ON THE EFFECT OF THE STRENGTH OF ACID SITES IN HETEROGENEOUS CATALYSTS ON THE ACTIVITY IN THE SKELETAL ISOMERIZATION OF n-BUTANE
V.P. Shmachkova, N.S. Kotsarenko, E.A. Paukshtis
Kinet. Catal., 45(4) (2004) pp. 554-557.
The catalytic activity of three groups of acid catalysts different in the nature and strength of acid sites in the skeletal isomerization of n-butane was studied. It was found that the strength of the sites did not correlate with the rate of the reaction.
THERMAL DECOMPOSITION OF NH4-ANALCIME
A.Yu. Likhacheva*, S.A. Veniaminov, E.A. Paukshtis (*Institute of Mineralogy and Petrology, Novosibirsk, Russia)
Phys. Chem. Miner., 31(5) (2004) pp. 306-312.
The thermal decomposition of ammoniumexhanged natural analcime is characterized by gas chromatography, IR spectroscopy and X-ray diffraction. The de-ammoniation and dehydroxylation proceed in parallel throughout the decomposition, which evidences the instability of the protonated analcime framework. The mechanism of degassing of NH4-analcime changes throughout its decomposition. At the initial step, the mechanism of de-ammoniation consists in thermal dissociation of NH4+ molecule onto NH3 and proton (framework OH group) and diffusion of NH3 out of the structure. Subsequent decomposition and removal of the OH groups lead to a progressive loss of crystallinity. At this step, an apparent activation energy for NH3 desorption is estimated to be 145(±13) kJ mol–1. This value is within the upper limit of the activation energy characteristic for the NH3 desorption from proton centres in large-pore zeolites. At the final step, the adsorption of NH3 and protons onto the defect centres in the amorphosed aluminosilicate framework results in a significant increase of an apparent activation energy for the de-ammoniation and dehydroxylation up to 270(±20) kJ mol–1.
METHANOL DEHYDROGENATION OVER COPPER-CONTAINING CATALYSTS MODIFIED BY CERIUM AND MANGANESE OXIDES
A.A. Vedyagin, N.O. Struikhina, P.G. Tsyrulnikov, A.V. Bubnov, N.V. Antonicheva
Catal. Ind., 3 (2004) pp. 14-17.
For the purpose of improvement of the catalytic characteristics of copper-containing catalysts for methanol dehydrogenation, a possibility of modifying them with cerium and manganese oxides has been investigated. The X-ray phase analysis and derivatography were used for determination of phase composition and the nature of phase transformations at different stages of preparation of the catalysts on two types of carriers. Introduction of modifiers leads to decrease in activity and selectivity to methylformate for the samples based on sibunit and improves cited catalytic properties for the samples based on silicate composite. A possible mechanism of different action of additives on catalyst activity is discussed.
RADICAL GENERATION IN THE COURSE OF N-UNDECANE PYROLYSIS ON BaCl2 AND THE DEFECT MAGNESIUM OXIDE
N.A. Vasilieva, R.A. Buyanov
Chem. Sustian. Devel., 12(6) (2004) p. 661-668.
Ethyl radical generation kinetics in the course of pyrolysis of n-undecane on BaCl2 and defect magnesium oxides is studied using radical freezing in the resonator of an ESR spectrometer. BaCl2 accelerates heterogeneous component, defect magnesium oxides accelerate homogeneous component of the process. BaCl2 activation energy E = 192 kJ/mol is lower than one for the thermal pyrolysis E = 322 kJ/mol. The phenomenon of surface “ignition” is found on the catalysts accelerating homogeneous component and making of the catalytic sphere. Thermal pyrolysis is performed between catalyst grains under temperature arising to a critical level. Then catalyst begins to generate additional radical, with activation energy typical of radical reactions E = 4 kJ/mol. Increase of the catalytic pyrolysis performance and selectivity through application of specific heterogeneous catalysts are suggested.
CHLORINATION OF METHANE OVER NANOCRYSTAL MAGNESIUM OXIDE
V.A. Averyanov*, Yu.D. Grudtsyn*, D.U. Grudtsyna*, S.A. Bagashov*, N.A. Pakhomov, A.M. Volodin, K.J. Klabunde** (*Tula State University, Tula, Russia; **Kansas State University, Manhattan, USA)
Proceedings of the Tula State University, ser. “Chemistry”, 4 (2004) pp. 45-50.
In a range of temperatures 300-350oC vapourphase chlorination of methane on a nanocrystal magnesium oxide has been investigated. It is shown that in comparison with industrial catalysts the nanocrystal MgO has much higher activity and selective actionю
SIMULATION OF X-RAY POWDER DIFFRACTION PATTERNS ON THE BASE OF THE MODELS OF IMPERFECT CRYSTALS
S.V. Cherepanova, S.V. Tsybulya
J. Mater. Sci. Forum, Trans Tech Publications Inc., Zurich, Switzerland, 443-444 (2004) pp. 87-90.
Software for the simulation of X-ray powder diffraction (XRPD) patterns for ultrafine grained materials with some kinds of imperfections has been developed. These calculations are performed on the base of the model of one dimensionally disordered crystal. Such a model can described stacking faults and other planar defects and also finite size of coherently scattering domains. Simulated XRPD pattern is compared with the experimental one and can be fitted to it. Potentialities of the software are illustrated by several examples.
PROTONATION SITE AND HYDROGEN BONDING IN ANHYDROUS AND HYDRATED CRYSTALLINE FORMS OF DOXAZOSINE MESYLATE FROM POWDER DATA
V.V. Chernyshev*, D. Machon**, A. Fitch*, S.A. Zaitsev*, A.V. Yatsenko*, A.N. Shmakov, H.-P.Weber** (*Moscow Lomonosov State University, Moscow, Russia; **Group "Structure of Materials under Extreme Conditions", Swiss-Norwegian Beam Lines at ESRF, Grenoble Cedex, France)
Acta Crystallogr., Sect. B: Struct. Sci., B59(Part 6) (2003) pp. 787-793.
The three-dimensional solid-state structures of two modifications of doxazosin mesylate (C23H26N5O5)+.(CH3SO3)-, 4-amino-2-[4-[(2,3-dihydro- 1,4-benzodioxin-2-yl)carbonyl]piperazin-1-yl]-6,7- dimethoxyquinazoline methanesulfonate, a commonly used antihypertensive agent, have been determined by synchrotron X-ray powder diffraction. An anhydrous form (A) and a dihydrate form (dG) crystallize in monoclinic space groups. In both forms the doxazosin molecule is protonated at the N1 atom of the quinazoline bicycle. The N1 atom, and the amino H atoms and O atoms of the mesylate moieties are involved in three-dimensional hydrogen-bonding networks, while solvent water molecules and carboxamide O atoms are also incorporated in a hydrogen-bonding network in dG.
X-RAY DIFFRACTION STUDY OF ZIRCONIA PILLARED CLAYS
D.A. Zyuzin, E.M. Moroz, T.G. Kuznetsova, V.A. Sadykov, V.P. Doronin
React. Kinet. Catal. Lett., 81(1) (2004) pp. 137-142.
X-ray powder diffraction (XRPD) and X-ray radial electronic distribution density (RED) of initial and zirconia-pillared interlayered clays (Zr-PILC) were studied. After pillaring, the basal (001) spacing was found to increase from 11 Å in the initial clay kept under air to 17.7 Å in Zr-PILC. The structure of zirconium nanopillars was characterized. The interatomic distances with corresponding coordination numbers obtained from the RED curves were close to those in zirconium tetramers.
LOCAL STRUCTURE OF AMORPHOUS AND HIGHLY DISPERSED ZIRCONIUM HYDROXIDES AND OXIDES
D.A. Zyuzin, E.M. Moroz, A.S. Ivanova, A.N. Shmakov, G.N. Kustova
Kinet. Catal., 45(5) (2004) pp. 739-742.
The local structure of amorphous and highly dispersed hydroxide and oxide zirconium compounds prepared from zirconyl nitrate solutions by precipitation was studied by an X-ray diffraction technique of radial electron distribution. It was found that X-ray amorphous precipitates were formed at 383 K. These precipitates were polynuclear hydroxo complexes, whose short-range ordering was similar to the structure of a cubic ZrO2 phase. A special feature of these formations, compared with the cubic oxide phase, is that the closest Zr–Zr distance in them is shortened by 0.2 Å, NO3 and OH groups are the constituents of an anionic sublattice, and the coordination number of Zr–anion distances is increased. Calcination at 653 K followed by cooling to room temperature resulted in the appearance of a monoclinic ZrO2 phase with a crystallite size of ~60 Å along with the cubic phase. The amount of the former phase depended on the pH of precipitation and on the presence of residual NO3 and OH groups in precipitates.
CONSTITUTION AND PROPERTIES OF NANOCOMPOSITES PREPARED BY THERMAL DECOMPOSITION OF SILVER SALTS SORBED BY POLYACRYLATE MATRIX
T.I. Izaak*, O.V. Babkina*, A.I. Boronin, T.N. Drebushchak**, A.I. Stadnichenko, G.M. Mokrousov* (*Tomsk State University, Tomsk, Russia; **Institute of Solid-State Chemistry and Mechanochemistry, Novosibirsk, Russia)
Colloid J., 65(6) (2003) pp. 720-725.
Constitution and dispersity of the products of thermal decomposition of silver nitrate ammonia complex sorbed by polyacrylate matrix are studied by the methods of small- and wide-angle X-ray scattering, optical, photoelectron and Auger-electron spectroscopies. It is shown that, at temperatures of 140–150°C, the complete decomposition of the complex occurs with the formation of nanoparticles and charged silver clusters in polymer bulk. No initial or intermediate products were observed. The average size of obtained nanoparticles is equal to 5 nm. The particles with the size less than 5 nm are amorphous according to X-ray data. The stabilization of nanoparticles occurs due to the adsorption of acrylic copolymer (presumably, via oxygen atoms) on their surfaces. Upon long-term storage in air, the selfdiffusion of silver particles and clusters takes place from the surface to composite bulk caused by the detachment of oxygen-containing groups occurring at the metal–polymer interface.
CLEANING OF THE SURFACE OF SILVER CRYSTALS USED AS CATALYSTS OF GAS-PHASE OXIDATION OF ETHYLENE GLYCOL TO GLYOXAL
A.S. Knyazev*, O.V. Vodyankina**, L.N. Kurina**, S.V. Koscheev, A.I. Boronin (*Institute of Petroleum Chemistry, Tomsk, Russia; **Tomsk State University, Tomsk, Russia)
Russ. J. Appl. Chem., 77(1) (2003) pp. 41-45.
The procedure for cleaning polycrystalline fibers of electrolytic silver used as a catalyst for gasphase oxidation of ethylene glycol to glyoxal was developed with the aid of X-ray photoelectron spectroscopy.
PLASMA CHEMICAL SYNTHESIS OF SILICON CARBONITRIDE FILMS
T.P. Smirnova*, A.M. Badalian*, V.O. Borisov*, V.V. Kaichev, L.F. Bakhturova*, V.I. Rachlin**, M.G. Voronkov**, R.G. Mirskov** (*Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia; **Favorsky Institute of Chemistry, Irkutsk, Russia)
Investigated in Russia, 147 (2004) pp. 1607-1615.
Silicon carbonitride thin films were synthesised with RP CVD process using the novel single-source precursors Me2HSiNHNMe2 and Me2Si(NHNMe2)2, which are derivative of 1,1-dimethylhydrazine. The films were characterized by XPS, FTIR, UV-vis and XANES spectroscopy as well as ellipsometry. Electrophysical properties were investigated using test MIS (metal-insulator-semiconductor) structures. Spectroscopy data showed that Si-N, Si-C and C-N are the main bonds for the films deposited from Me2HSiNHNMe2 whereas Si-N and C-N are basic bonds for the films obtained using Me2Si(NHNMe2)2. The films represent SixNyCz alloys of variable composition. Chemical composition, optical and electrophysical properties of the films and MIS structures are dependent on the deposition conditions.
APPLICATION OF SCANNING TUNNELING MICROSCOPY AND X-RAY PHOTOELECTRON SPECTROSCOPY IN THE INVESTIGATION OF THE SINTERING OF Ag/Al2O3 MODEL SUPPORTED CATALYSTS
A.V. Nartova, R.I. Kvon
Kinet. Catal., 45(5) (2004) pp. 730-734.
The results of a study of a specially prepared Ag/Al2O3 model system by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) are presented. The surface morphology of a model support (a thin alumina film on a conducting support) and a model supported catalyst (Ag/Al2O3) was characterized using STM. The first experimental results obtained in the STM and XPS study of the sintering of supported catalysts are reported, which demonstrate the capabilities of these techniques for studies of this kind.
NANOWIRE ARRANGEMENTS OF PbS-Sb2S3-COMPOUNDS
M. Heuer*, G. Wagner*, T. Doering*, K. Bente*, G.N. Kryukova (*Institute of Mineralogy, Crystallography and Materials Science, University of Leipzig, Leipzig, Germany)
J. Cryst. Growth, 267(3-4) (2004) pp. 745-750.
In analogy to PbS–Sb2S3-minerals nanowires of synthetic boulangerite (Pb5Sb4S11) with diameters ranging from 100 to 500 nm and lengths up to 100 μm were crystallized from the melt. In most cases these nanowires are arranged like bundles and microtubes, which are inspected by scanning electron microscopy. The chemical composition of these materials was analysed by electron microprobe and transmission electron microscope adapted energy dispersive X-ray analysis. The lattice parameters of natural and synthetic boulangerite nanomaterials were determined by powder X-ray diffraction. The crystal structure was examined by means of high resolution transmission electron microscopy, whereby the relation between structure and morphology was studied and the material was checked regarding cation ordering.
X-BAND PERPENDICULAR-MODE EPR SPECTRA OF ‘EPR SILENT’ MANGANESE(III) PORPHYRINS
E.P. Talsi, K.P. Bryliakov
Mendeleev Commun., 14(3) (2004) pp. 111-112.
The X-band perpendicular-mode EPR spectra of manganese(III) porphyrins were detected for the first time.
INVESTIGATION OF FRAGMENTATION PATTERN OF BIS(TRIMETHYLSILYL) ESTER OF 3-MERCAPTOPROPIONIC ACID
A.I. Potapov, A.V. Vorontsov
Intern. J. Mass Spectrom., 235(2) (2004) pp. 163-170.
The routes of fragmentation of the parent molecule resulting from electron impact ionization have been studied in a quadrupole ion trap using collision induced dissociation (CID) of fragments. Fragmentation of the parent molecular ion m/z 250 results in major ions 235, 178, 163, 135, 129, 75, 73, and 55. While some fragments are easily assigned according to literature - m/z 235 to [M − CH3]+, m/z 73 to [Si(CH3)3]+, m/z 75 to [Si(CH3)2OH]+, and m/z 55 to [CH2CHCO]+ - other ions required CID to obtain their structure. Fragment m/z 178 was found to emerge from breaking of Si---S bond and hydrogen rearrangement in the molecular ion. Fragment m/z 163 is formed by elimination of CH3 group from ion m/z 178. Elimination of H2S from ion m/z 163 leads to formation of the ion m/z 129. Another route is elimination of molecule CO from ion m/z 163 to form ion m/z 135. Fragmentation of ion m/z 129 by elimination of neutral molecule CO2 leads to emerging of ion m/z 85. For supporting the assumed structure of ions m/z 178, 163, 135, quantum chemical calculations were performed using methods PM3 and DFT. The calculations demonstrated that these ions have TMS group attached to the carboxyl group. The stability of the ions is associated with forming cyclic structures containing new bonds S---O (m/z 178), O---Si (m/z 163) and S---Si (m/z 129). Molecular dynamics calculations confirmed that these structures are the most stable conformations of the ions.
NMR DETERMINATION OF THE TOTAL COMPOSITION OF COMMERCIAL ABSORBENTS BASED ON MONOETHANOLAMINE
V.P. Talzi
Russ. J. Appl. Chem., 77(3) (2004) pp. 430-434.
The composition of aqueous solution of monoethanolamine used in various units of gas treatment of the Omsk Oil-Refining Plant, Joint-Stock Company, was studied by the 13C NMR spectroscopy. The components of the gases to be purified and the reactions producing the impurities were established.
OLIGOMERIC FORMS OF TIN(IV) IN THE Rb2Sn(OH)6-H2O-H2O2-Rb2Sn(OOH)6 SYSTEM AS PROBED BY 119Sn AND 17O NMR
P.V. Prikhodchenko*, E.A. Ustinova**, M.A. Fedotov, E.G. Ippolitov* (*Kurnakov Institute of General and Inorganic Chemistry, Moscow, Russia; **Moscow Pedagogical State University, Moscow, Russia)
Russ. J. Inorg. Chem., 49(10) (2004) pp. 1562-1567.
Solutions of the Rb2Sn(OH)6-H2O-H2O2-Rb2Sn(OOH)6 system with different [H2O2]/[H2O] ratios were studied by 119Sn and 17O NMR. A broad 119Sn NMR signal in the range from –590 to –610 ppm was assigned to Sn(IV) oligomeric forms with bridging peroxo groups. The conditions of their formation and stability range were determined. The first 17O NMR characteristics of the peroxo groups coordinated to the tin(IV) atom were obtained.
HYDROLYSIS OF VOLATILE AMMONIUM OXOFLUOROTITANATE ACCORDING TO 19F, 17O, AND 49Ti NMR DATA
N.M. Laptash*, M.A. Fedotov, I.G. Maslennikova* (*Institute of Chemistry, Vladivostok, Russia)
J. Struct. Chem., 45(1) (2004) pp. 74-82.
Hydrolysis of NH4TiOxF5-2x (x ≤ 0.4) (I) was investigated by 19F, 17O, and 49Ti NMR. The interaction of complex I with water is accompanied by the formation of [TiF6]2- and multinuclear titanium forms. The composition of the main forms resulting from hydrolysis of I has been established. The bonding of titanium octahedra into dimers and other oligomers occurs by formation of hydroxyl bridges, considerably lowering the pH of the solution. Close analogy has been found between hydrolysis of the title complex and that of titanium tetrafluoride.
STATE OF MOLECULES AND IONS IN THE STRUCTURAL CHANNELS OF SYNTHETIC BERYL WITH AN AMMONIUM IMPURITY
R.I. Mashkovtsev*, E.S. Stoyanov, V.G. Thomas* (*Trofimuk United Institute of Geology, Geophysics, and Mineralogy, Novosibirsk, Russia)
J. Struct. Chem., 45(1) (2004) pp. 56-63.
The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containing solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy it was found that water molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination at high temperatures close to the decomposition temperature. On exposure to g radiation at 77 K, the paramagnetic NH3 + and H0 radicals are stabilized in the structural channels of beryl. In addition to the known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well. For one of the additional radicals, Hb, the model of atomic hydrogen stabilized at the center of a silicon-oxygen ring with two water molecules in adjacent cavities is suggested.
FERROMAGNETIC RESONANCE OF NICKEL NANOPARTICLES IN AN AMORPHOUS OXIDE MATRIX
M.M. Yulikov, I.S. Abornev, O.N. Martyanov, V.F. Yudanov, V.P. Isupov*, L.E. Chupakhina*, K.A. Tarasov*, R.P. Mitrofanova* (*Institute of Solid-State Chemistry and Mechanochemistry, Novosibirsk, Russia)
Kinet. Catal., 45(5) (2004) pp. 735-738.
The formation of a ferromagnetic phase in the thermal decomposition of a layered lithium–aluminum double hydroxide with intercalated nickel–EDTA complexes was studied using ferromagnetic resonance (FMR) spectroscopy. The FMR spectra were simulated based on a superparamagnetic narrowing model. Data on the size and shape of the resulting nickel nanoparticles were calculated.
SYNTHESIS AND ADSORPTION PROPERTIES OF INTIMATELY INTERMINGLED MIXED METAL OXIDE NANOPARTICLES
G.M. Medine*, V.I. Zaikovskii, K.J. Klabunde* (*Department of Chemistry, Kansas State University, Manhattan, USA)
J. Mater Chem., 14(4) (2004) pp. 757-763.
A series of intimately intermingled mixed metal oxide nanoparticles were prepared via a modified aerogel procedure (MAP). These mixed oxides were composed of alkaline earth oxides and aluminas. It was found that the surface area and reactivity of these materials decreased on going from magnesium to barium in these intimately intermingled metal oxides. The samples were analyzed by HRTEM and the images obtained illustrate the degree of mixing throughout each of the intermingled mixed metal oxides. As well as synthesizing and characterizing these samples, standardized adsorption tests were also carried out and compared to those of individual metal oxide nanoparticles and physical mixtures of metal oxide nanoparticles. The following tests have been shown to be effective in determining the adsorption properties of metal oxide nanoparticles: (i) destructive adsorption of paraoxon (a surrogate of the chemical warfare nerve agent, VX) and (ii) the adsorption of acid gases. The data clearly show enhanced kinetics and capacities for the intermingled AP-MgAl2O4 and indeed, the data suggest that surface reactivities can be tailored by the aerogel mixing process.
THE STATUS OF THE KEDR ASHIPH SYSTEM
A.Yu. Barnyakov*, M.Yu. Barnyakov*, V.S. Bobrovnikov*, A.R. Buzykaev*, A.F. Danilyuk, S.A. Kononov*, E.A. Kravchenko*, G.D. Minakov*, A.P. Onuchin*, V.A. Rodiakin*, G.A. Savinov*, V.A. Tayursky* (*Budker Institute of Nuclear Physics, Novosibirsk, Russia)
Nucl. Instrum. Methods Phys. Res., Sect. A, 518(1-2) (2004) pp. 597-601.
Cherenkov counters based on Aerogel, wavelength SHIfter, and PHotomultipliers (ASHIPH) for the KEDR detector are described. As compared with the direct light collection on PMT, the ASHIPH method allows us to diminish the number of PMTs essentially. The quality of the particle identification with the ASHIPH counters was tested. The small π/K separation is 4.5σ for the momentum 1.2 GeV/c. The mass production of the ASHIPH counters was organized in Budker Institute of Nuclear Physics (Novosibirsk, Russia). 80 counters filled with 500 ls of aerogel have been produced and tested with cosmic muons. These counters were installed into the KEDR detector in 2003. The stability of the micro-channel PMTs without protecting layer was studied. The first results on a long-term stability of the ASHIPH counters filled with the hygroscopic aerogel are presented.
IR SPECTRA OF PARACETAMOL AND PHENACETIN. I. THEORETICAL AND EXPERIMENTAL STUDIES
E.B. Burgina, V.P. Baltakhinov, E.V. Boldyreva*, T.P. Shakhtschneider* (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia)
J. Struct. Chem., 45(1) (2004) pp. 64-73.
IR spectra of paracetamol and phenacetin have been measured for powder crystals of these compounds and for their solutions in chloroform and dimethylsulfoxide. Ab initio calculations of their equilibrium geometry and vibrational spectra were carried out for spectrum interpretation. Differences between the experimental IR spectra of solutions and crystalline samples have been analyzed. Variations of molecular structure from the isolated state to molecular crystal were estimated based on the difference between the optimized molecular parameters of free molecules and the experimental bond lengths and angles evaluated for the crystal forms of the title compounds. The role of hydrogen bonds in the structure of molecular crystals of paracetamol and phenacetin is investigated, and spectral ranges with maximal intermolecular interactions are determined.
A STRONG ACID THAT DOES NOT PROTONATE WATER
E.S. Stoyanov, Kee-Chan Kim*, Ch.A. Reed* (*Department of Chemistry, University of California, Riverside, California)
J. Phys. Chem. A, 108(42) (2004) pp. 9310-9315.
The nature of solvated acids in benzene and chlorinated hydrocarbon solvents is sensitively revealed by IR spectroscopy. Two similarly strong, structurally related acids, triflic acid (CF3SO3H) and the N-H acid bis(trifluoromethylsulfonyl) imide ((CF3SO2)2NH), behave quite differently toward water in these media. Triflic acid protonates water at the one-equivalent level to give the hydronium ion, H3O+. By contrast, bis(trifluoromethylsulfonyl) imide forms a simple hydrate, (CF3SO2)2NH···OH2, even with water at the two-equivalent level. The difference arises from the differing abilities of the conjugate base anions to engage in H-bonding and ion pairing. It illustrates how acidity in low-dielectric media is critically dependent on the nature of the conjugate base anion. νO-H and νN-H stretching frequencies indicate that the H-bonding acceptor ability for solvents toward acidic protons increases in the order carbon tetrachloride < benzene ~ 1,2-dichoroethane < water. With benzene, a marked tendency for acidic protons to H-bond to the π-face of the arene ring is noted and an IR signature of this solvation mode is observed.
UNEXPECTED IR CHARACTERISATION OF HYDROGEN BONDS IN THE 18-CROWN-6-ETHER COMPLEX OF THE Н3О+ HYDRONIUM ION. CAN THE LOCATION OF THE PROTONS BE SPECIFIED?
E.S. Stoyanov, Ch.A. Reed* (*Department of Chemistry, University of California, Riverside, California)
J. Phys. Chem. A, 108(5) (2004) pp. 907-913.
The νas(C-O-C) IR spectral signatures of polyethers in H-bonded hydronium ion complexes have been established in studies of H3O+ and H5O2+ complexes with 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and their open chain poly(ethylene glycol) analogues in 1,2-dichoroethane solutions. When experiment meets theory in the structure of the H3O+·18-crown-6 complex, there is disagreement. While DFT calculations at the BLYP/II'//BLYP/6-31G* level indicate a C3v structure with three normal, static linear H bonds to alternate O atoms of the crown ether, IR spectroscopy in the ν(C-O-C) region indicates that all six O atoms are equivalent. A new type of low-barrier H-bonding involving rotational mobility of H3O+ is proposed to rationalize the experimental observations.
NANOCLUSTERS AS PRECURSORS TO (MoVW)5O14: IN SITU AND CHEMICAL CHARACTERIZATION OF THE SYSTEMS OF A SINGLE PHASE OXIDATION CATALYST
S. Knobl*, G.A. Zenkovets, G.N. Kryukova, R.I. Maksimovskaya, T.V. Larina, N.T. Vasenin, V.F. Anufrienko, D. Niemeyer*, R. Schlögl* (*Fritz-Haber-Institut der MPG, Berlin, Germany)
Phys. Chem. Chem. Phys., 5(23) (2003) pp. 5343-5348.
The ternary oxide (MoVW)5O14 is considered to be highly significant for catalytic, mild selective oxidation reactions. By using UV/Vis, EPR, 95Mo NMR spectroscopies and conductivity measurements the coordination chemistry of the molybdate species in the precursor solutions was studied. This work has established that mixing the precursor solutions (ammonium heptamolybdate, ammonium metatungstate and vanadyl oxalate) forms a polymeric network in which the vanadyl species act as a linker between the molybdate species. The addition of tungsten atoms significantly enhances the polymerisation process.
LINEAR NANOSCALE CLUSTERS OF CuO IN Cu-ZSM-5 CATALYSTS
Z.R. Ismagilov, S.A. Yashnik, V.F. Anufrienko, T.V. Larina, N.T. Vasenin, N.N. Bulgakov, S.V. Vosel, L.T. Tsykoza
Appl. Surf. Sci., 226(1-3) (2004) pp. 88-93.
The electron states of copper have been studied by ESR and UV-Vis as a function of the method used for preparation of Cu-ZSM-5 (ion-exchange, wet impregnation, and deposition), synthesis conditions (pH of copper solution, copper precursor, temperature, etc.) and copper loading. For calcined Cu-ZSM-5 samples treated under vacuum at 400°C, axial ESR spectra of O− ion radicals (g┴=2.05, g||=2.02), which are presumably assigned to linear ---O−---Cu+---O−---Cu+---O−-chains in zeolite channels, are observed. The same samples treated under vacuum at 150–400°C, exhibit UV-Vis absorption bands at the unexpected region of 18,000– 23,000 cm−1. They are assigned to the ligand–metal charge transfer bands in ---O2−---Cu2+---O2−---Cu2+---O2−- like chains in the zeolite channels. Along with these states, isolated octahedral Cu2+ ions with different extents of tetragonal distortion (absorption band (a.b.) 12,500–14,000 cm−1) and clustered copper oxide species (charge transfer band (CTB) 27,000– 32,000 cm−1) are also observed.
FORMATION OF NANOCRYSTALLINE STRUCTURES IN A Co-Al SYSTEM BY MECHANICAL ALLOYING AND LEACHING
G.V. Golubkova*, O.I. Lomovsky*, Y.S. Kvon**, A.A. Vlasov, A.L. Chuvilin (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia; **Research Center for Machine Parts and Materials Processing, University of Ulsan, South Korea)
J. Alloys Compd., 351(1-2) (2003) pp. 101-105.
Phase composition of the materials obtained by mechanical alloying of system Co–Al (Al concentration ranges from 50 to 70 at.%) and removal of aluminum from such alloys was investigated by differential dissolution, X-ray phase analysis and TEM with a resolution of 0.4 nm. The intensive mechanical alloying provides formation of the nanocomposite material containing both amorphous phase Co2Al5 and nanocrystalline particles of phase CoAl. Leaching of amorphous phase Co2Al5 results in the amorphous cobalt containing admixtures of alumina and hydroxide. Nanocomposite amorphous phase Co2Al5 and CoAl convert into nanocomposite amorphous Co and b.c.c. Co.
A NEW MESOPOROUS TITANIUM-SILICATE Ti-MMM-2: A HIGHLY ACTIVE AND HYDROTHERMALLY STABLE CATALYST FOR H2O2-BASED SELECTIVE OXIDATIONS
O.A. Kholdeeva, M.S. Melgunov, A.N. Shmakov, N.N. Trukhan, V.V. Kriventsov, V.I. Zaikovskii, V.N. Romannikov
Catal. Today, 91-92 (2004) pp. 205-209.
Physico-chemical characterisation and catalytic properties of a new hydrothermally stable mesoporous mesophase titanium-silicate, denoted as Ti-MMM-2, synthesised under moderately acidic conditions are reported. Structure and texture were characterised by using X-ray diffraction, N2 adsorption and TEM. The state of titanium was characterised using DRS-UV and XANES techniques. Catalytic properties of Ti-MMM-2 were tested in oxidation of three large organic substrates, 2,3,6-trimethylphenol, caryophyllene, and methyl phenyl sulfide, and compared with catalytic properties of TS-1 and Ti-MMM (titanium-silicate of the MCM-41 type synthesised under weakly alkaline conditions). The catalytic activity of Ti-MMM-2 is considerably higher compared to the activity of microporous TS-1 and similar to that of Ti-MMM. The performed physicochemical study implicated that Ti-MMM-2 combines marked accessibility of titanium and its high dispersion that ensure high catalytic activity of this material. By contrast to Ti-MMM, Ti-MMM-2 is hydrothermally stable and can be used repeatedly without deterioration of catalytic properties. A blend of high catalytic activity and hydrothermal stability allows to consider Ti-MMM-2 as a promising catalyst for the selective oxidation of large organic molecules with aqueous H2O2.
PATHWAYS OF DIRECTED SYNTHESIS OF IRON(II) CLATHROCHELATES AND POLYCLATHROCHELATES WITH NONEQUIVALENT CAPPING GROUPS STARTING FROM ANTIMONY- AND GERMANIUMCONTAINING PRECURSORS
Y.Z. Voloshin*,***, O.A. Varzatskii**, S.V. Korobko**, M.Y. Antipin***, I.I. Vorontsov***, K.A. Lyssenko***, D.I. Kochubey, S.G. Nikitenko, N.G. Strizhakova** (*Karpov Institute of Physical Chemistry, Moscow, Russia; **Vernadskii Institute of General and Inorganic Chemistry, Kiev, Ukraine; ***Nesmeyanov Institute of Organoelement Compounds, Moscow, Russia)
Inorg. Chim. Acta., 357(11) (2004) pp. 3187-3204.
Alternative methods for directed syntheses of clathrochelates and polyclathrochelates with two nonequivalent capping fragments using semiclathrochelate precursors and capping group reactions are described. The lability of antimonycapped iron(II) clathrochelates in remetallation (a capping group exchange) reactions allowed to obtain of mono- and bis-clathrochelates of a general formula FeNx3X1X2 and (FeNx3X1)2X2 (where Nx2− is cyclohexanedione-1,2-dioxime dianion; X1, X2 are different capping groups). The first and unique dioximate [Fe(HNx)3(Sb(C6H5)3)](ClO4) semiclathrochelate was isolated and characterized. The reaction of this complex with differing mono- and bifunctional cross-linking agents (Lewis acids) led to the formation of clathrochelates molecules with nonequivalent capping groups. The clathrochelates with a labile triethylantimony capping group underwent remetallation in the presence of silicon dioxide as a catalyst. The first stage led to the formation of a surface-immobilized mixed SbSi-capped clathrochelate, which under the action of another capping agent desorbed from the surface gives a mono- or bis-clathrochelate depending on the nature of this agent. An alternative pathway using the biscapping agents has been implemented for synthesis of bis-clathrochelates when reactive fragments of an initial azomethine ligand demonstrate essentially different chemical properties. The oximehydrazonate germanium-capped iron(II) bis-clathrochelate was synthesized starting from a bis-semiclathrochelate, which was initially isolated with bis-capping germanium(IV) tetraethoxide. A further H+-catalyzed macrocyclization with triethyl orthoformate produced germanium-capped bis-clathrochelate. The obtained mono- and bis-clathrochelates have been characterized using elemental analysis, PD mass, IR, UV–Vis and 1H and 13C NMR spectra, and X-ray crystallography (for FeNx3(Sb(C2H5)3)2 complex), as well as by cyclic voltammograms. The distortion angle ϕ values and the main distances in the clathrochelate frameworks have been deduced using 57Fe Mössbauer parameters, and EXAFS data and molecular mechanics calculations, respectively.
ANALYTICAL CHEMISTRY OF PHASES OF VARIABLE COMPOSITION AND THE PRINCIPLES OF STOICHIOGRAPHIC DETERMINATION OF SUCH PHASES IN MULTIELEMENT MULTIPHASE SAMPLES
V.V. Malakhov, A.A. Vlasov, L.S. Dovlitova
J. Analyt. Chem., 59(11) (2004) pp. 1016-1026.
The general problems of determining the stoichiometry and content of solid phases of variable composition in multielement multiphase substances are discussed. The possibilities and conditions of application of a reference-free stoichiographic method based on the differential dissolution (DD) of components for the analysis of samples containing spatially homogeneous and inhomogeneous phases are considered. The results of mathematical modeling of the DD process for a mixture of phases of constant and variable composition are presented. These data substantiate the use of the stoichiogram affinity criterion for the identification of spatially inhomogeneous phases of variable composition. Examples of applying the DD method to the phase analysis of various substances containing phases of variable composition are given.
STRUCTURE, STOICHIOMETRY, AND MAGNETIC PROPERTIES OF THE LOW DIMENSIONAL STRUCTURE PHASE LiCuVO4
A.V. Prokofiev*, I.G. Vasilyeva**, V.N. Ikorskii**, V.V. Malakhov, I.P. Asanov***, W. Assmus* (*Physikalisches Institut, J.W. Goethe Universität, Frankfurt a.M., Germany; **Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia; ***Samsung Advanced Institute of Technology, Suwon, South Korea)
J. Solid State Chem., 177(9) (2004) pp. 3131-3139.
A systematic investigation of a series of singleand polycrystalline LiCuVO4 samples by means of X-ray diffraction, X-ray photoelectron spectroscopy, differential dissolution analysis, and magnetic susceptibility measurement were performed. This study reveals a noticeable difference in stoichiometry and structure of the samples prepared in different ways. The magnetic properties are discussed with respect to phase inhomogeneity, non-stoichiometry and structural defects.
CHEMICAL COMPOSITION OF SURFACE LAYERS OF ATMOSPHERIC AEROSOLS OF BAIKAL REGION BY METHOD OF SECOND IONIC MASS-SPECTROMETRY
V.P. Ivanov, S.N. Trukhan. D.I. Kochubey, O.G. Netsvetaeva*, L.V. Golobkova*, T.V. Khodzher* (*Limnological Institute, Irkutsk, Russia)
Chem. Sustain. Devel., 12(1) (2004) pp. 165-173.
Secondary ion mass spectrometric technique was used to study elemental and phase composition of surface layers of two types of atmospheric aerosols drawn in Irkutsk (Listvyanka village) and at the highlevel station Mondy. The first type aerosols were the ones sampled by pumping air through filters, and another type aerosol particles were captured during snowfalls and collected by pumping the melted snow through filters. The action of water was established to result in “leaching” Na, Ca and Ti from the surface layers to form hydroaluminosilicates. Therefore, the considerable dispersion of element concentrations in the surface layers of air aerosols may be accounted for by the action of atmospheric moisture on the aerosols which depends on the residence time of the aerosols in the atmosphere.
DISSOCIATION CONDITIONS OF METHANE HYDRATE IN MESOPOROUS SILICA GELS IN WIDE RANGES OF PRESSURE AND WATER CONTENT
E.Ya. Aladko*, Y.A. Dyadin*, V.B. Fenelonov, E.G. Larionov*, M.S. Melgunov, A.Yu. Manakov*, A.N. Nesterov*, F.V. Zhurko* (*Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia)
J. Phys. Chem. B, 108(42) (2004) pp. 16540-16547.
The temperature of methane hydrate dissociation in silica mesopores has been monitored within a wide range of pressures from 10 MPa to 1 GPa. Because the determination of pore size appears to be crucial for the studied phenomenon, several methods of calculation have been applied. According to our findings, the size that corresponds to the mean size of the most representative pores is to be considered as the most reliable. It was concluded that the shape of hydrate particles replicates a host space of pores and may have a complex (e.g., fractal) shape. An attempt to simulate the curvature of hydrate particles by globular (quasispherical), elongated (quasi-cylindrical), or any intermediate models has been done. The quasispherical model seems to be more adequate for hydrate particles in small pores (<8 nm), while the quasi-cylindrical model fits better the experimental data for hydrate particles in larger pores. According to experimental results, the hydrate can be formed in pores only by capillary condensate, without in-volving the water layers tightly bound by the surface, and pressure has an insignificant effect on the decrease of the dissociation temperature of the confined hydrate. A new effect of the formation of hydrates at a temperature higher than the bulk hydrate dissociation temperature has been observed for silica gels with the narrowest pores studied.
MECHANOCHEMICAL SYNTHESIS OF YTTRIUM AND LANTHANUM TANTALATES
V.V. Molchanov, M.G. Zuev, L.M. Plyasova, S.V. Bogdanov
Inorg. Mater., 40(1) (2004) pp. 83-89.
The phase changes in the Y2O3–Ta2O5 and La2O3–Ta2O5 systems during mechanical activation and subsequent heat treatment are investigated. Y2O3 and Ta2O5 are shown to react during mechanical activation to form Y3TaO7. Calcination of activated mixtures leads to the formation of YTaO4 and LaTaO4. The observed processes are interpreted in terms of transformations of the fluorite structure. A new method is proposed for the synthesis of rare-earth tantalates for applications in diagnostic X-ray contrast media. The method has a number of important advantages over the conventional ceramic route.
MECHANOCHEMICAL SYNTHESIS OF INTERMETALLIC HYDRIDES AT ELEVATED HYDROGEN PRESSURES
V.V. Goidin, V.V. Molchanov, R.A. Buyanov
Inorg. Mater., 40(11) (2004) pp. 1165-1168.
An apparatus is described for producing gas pressures of up to 10 MPa in the grinding vessels of a planetary mill. Mechanochemical reactions are carried out for the first time at gas pressures above 1 MPa. A novel approach to the synthesis of intermetallic hydrides is proposed which involves mechanical activation of a metal mixture at a high hydrogen pressure. Using this approach, two new hydrides are synthesized: Mg2NiH6 and a magnesium copper hydride with the approximate composition MgCuH2.
EFFECT OF MECHANOCHEMICAL ACTIVATION ON THE CATALYTIC PROPERTIES OF ZINC OXIDE
V.V. Molchanov, R.A. Buyanov, S.V. Tsybulya, G.N. Kryukova, A.N. Shmakov, A.I. Boronin, A.M. Volodin
Kinet. Catal., 45(5) (2004) pp. 684-693.
The reasons for changes in catalytic activity as a function of the time of mechanochemical activation in a planetary mill were studied with the use of a set of physicochemical techniques. The dependence of the specific rate of CO oxidation on the time of mechanochemical activation exhibited an extremal character. Small-angle interblock boundaries, disordered dislocations, and shear defects were formed in the sample with maximum activity because of mechanochemical activation. The linear dependence of the specific rate of CO oxidation on the value of microstresses suggested that the above defects were responsible for an increase in the catalytic activity. It is likely that oxygen atoms situated at the sites of the outcrop of defects on the surface served as elementary active centers.
MECHANOCHEMICAL SYNTHESIS AND REACTIVITY OF La1-xSrxFeO3-y PEROVSKITES
I.S. Yakovleva, L.A. Isupova, S.V. Tsybulya, A.V. Chernysh, N.N. Boldyreva, G.M. Alikina, V.A. Sadykov
J. Mater. Sci., 39(16-17) (2004) pp. 5517-5521.
Mechanochemical synthesis of La1-xSrxFeO3-y (0 ≤ x ≤ 1) perovskites was carried out from simple oxides. Undoped lanthanum ferrite samples calcined at 900 and 1100oC for 4 hours are nearly single-phase systems, while some substituted ones (samples with 0.3 ≤ x ≤ 0.8 calcined at 900°C and samples with x=0.3, x=0.4 and x=0.8 calcined at 1100°C) are two-phase systems consisting of orthorhombic perovskite La1-xSrxFeO3-y (A) and tetragonal perovskite SrzLa1-xSrxFeO3-y (B) phases. In CO and CH4 oxidation processes the specific catalytic activity (SCA) of samples calcined at 1100°C varies non-monotonously with the Sr content. In CO oxidation SCA reaches a maximum in the range of La substitution by Sr where phase transition occurs and samples are comprised of two coexisting phases (x=0.3 and 0.8). In CH4 oxidation SCA decreases with the Sr content.
THE EFFECT OF HYDROTHERMAL CONDITIONS ON THE MESOPOROUS STRUCTURE OF TiO2 NANOTUBES
D.V. Bavykin, V.N. Parmon, A.A. Lapkin*, F.C. Walsh* (*University of Bath, Bath, UK)
J. Mater. Chem., 14(22) (2004) pp. 3370-3377.
A systematic analysis of the influence of preparation conditions in the alkali hydrothermal synthesis on the morphology of TiO2 nanotubes is performed using HRTEM and low temperature nitrogen adsorption. The possible mechanisms of nanotube formation are reviewed and a mechanism based on the key stage of wrapping of intermediate multilayered titanate nanosheets is suggested. The driving force for wrapping is considered to be the mechanical stress arising during crystallisation/dissolution. The average diameter of the nanotubes was found to depend on the temperature and on the ratio of weight of TiO2 to the volume of sodium hydroxide solution. An increase in the temperature from 120 to 150°C results in an increase in the average nanotube diameter. Subsequent increases in the temperature result in the formation of non-hollow TiO2 nanofibers with an average diameter of 75 nm, a wide distribution in diameter and a length in excess of 10 μm. The increase of the TiO2 : NaOH molar ratio results in an increase in the average diameter of nanotubes and a decrease of surface area. The average inner diameter of TiO2 nanotubes varied between 2 and 10 nm. The pore-size distribution was evaluated from TEM, and low-temperature nitrogen adsorption data using the BJH method. It was shown that nitrogen adsorption is a suitable method for characterisation of the pore morphology of nanotubes.
POROUS COMPOSITES BASED ON OXIDE-ALUMINUM CERMETS (SYNTHESIS AND PROPERTIES)
S.F. Tikhov, V.E. Romanenkov*, V.A. Sadykov, V.N. Parmon, A.I. Ratko** (*Belarusian National Technical University, Minsk, Belarus; **Institute of General and Inorganic Chemistry, Minsk, Belarus)
Manuscript, Publishing House of SB RAS, “Geo” Branch, Novosibirsk, 2004, 205 p.
The manuscript is devoted to the physicochemical fundamentals of synthesis of porous ceramometals (cermets): Al2O3/Al, Me/Al2O3/Al, MeOx/Al2O3/Al, as well as ceramic composites on their bases, prepared through hydrothermal oxidation of powdered aluminum followed by calcination. The manuscript includes a detailed description of all stages of the preparation and the main properties of the composites (mechanical, textural, thermophysical, and catalytical). Special attention was paid to the relation between the parameters of synthesis and properties of cermets. A series of kinetic and balance equations has been obtained, which permit one to predict the properties of composite materials. The manuscript has no analogs in Russia and abroad as it is based upon the authors’ results obtained for the last 15 years. The manuscript is partially a reference book as it includes summarizing figures, diagrams, and tables. The manuscript is useful for specialists in the field of the preparation of porous materials as well as for engineers and students.
POROUS Al2O3/Al METAL CERAMICS PREPARED BY THE OXIDATION OF ALUMINUM POWDER UNDER HYDROTHERMAL CONDITIONS FOLLOWED BY THERMAL DEHYDRATION. IV. EFFECT OF OXIDE ADDITIVES ON THE COMPOSITION AND TEXTURE CHARACTERISTICS OF MOx/Al2O3/Al COMPOSITES
S.F. Tikhov, Yu.V. Potapova, V.B. Fenelonov, V.A. Sadykov, A.N. Salanov, S.V. Tsybulya, L.F. Melgunova
Kinet. Catal., 45(4) (2004) pp. 607-617.
The synthesis, structure, and texture of metal ceramics based on Al2O3/Al with powdered oxide additives (CaO, MgO, Al2O3, La2O3, and TiO2) were studied. Analytic expressions were derived to relate the main macroscopic characteristics of the composites.
THE EFFECT OF SUPPORT NATURE AND THE TEMPERATURE OF PRELIMINARY CALCINATION ON THE ATOMIC CATALYTIC ACTIVITY OF SUPPORTED PALLADIUM CATALYSTS FOR THE COMPLETE OXIDATION OF HYDROCARBONS
D.P. Chzhu, P.G. Tsyrulnikov, G.N. Kryukova, V.F. Borbat*, E.N. Kudrya, M.D. Smolikov, A.V. Bubnov (*Omsk State University, Omsk, Russia)
Kinet. Catal., 45(3) (2004) pp. 406-413.
It is shown that for palladium catalysts supported on various supports, there is no effect of thermal activation consisting of an increase in the turnover number (TON) of palladium with an increase in the temperature of sample calcination from 500 to 700°C, as was observed in the case of similar supported platinum catalysts; for two palladium–alumina catalysts calcined at 500°C and differing in the concentration of palladium and dispersity, the TON of low-dispersity palladium is substantially higher than the TON of high-dispersity palladium; all other conditions being the same, the TON of supported palladium is determined by the support nature.
FORMATION OF THE PORE STRUCTURE OF OXIDE VANADIUM-TITANIUMPHOSPHORUS CATALYSTS IN THE COURSE OF THERMAL TREATMENT
V.Yu. Gavrilov, G.A. Zenkovets, O.V. Zalomaeva, S.V. Tsybulya
Kinet. Catal., 45(5) (2004) pp. 702-707.
The effect of the conditions of the thermal treatment of vanadium–titanium–phosphorus catalysts on the formation of the pore structure and phase composition was studied. It was found that the optimum doping of catalysts with phosphorus (5 wt % P2O5) was favorable for retention of the high dispersity of primary particles up to 450°C. The main change in the texture of the catalysts occurred within the range of micropores and mesopores with D < 10 nm. The formation of the coarsely dispersed well-crystallized phase of a vanadium–titanium– phosphorus compound was detected.
DEVELOPMENT OF NOVEL CATALYSTS AND PROCESSES FOR SELECTIVE REDUCTION OF NITROGEN OXIDES BY HYDROCARBON IN EXCESS OXYGEN
V.A. Sadykov, V.V. Lunin*, A.Ya. Rozovskii**, V.A. Matyshak***, J. Ross**** (*Moscow Lomonosov State University, Moscow, Russia; **Intitute of Petrochemical Synthesis, Moscow, Russia; Institute of Chemical Physics, Moscow, Russia; ****University of Limerick, Limerick, Ireland)
In “Green Chemistry in Russia”, Eds. V. Lunin, P. Tundo, E. Lokteva, Moscow Lomonosov State University, 2004, pp. 64-100.
The authors summarize results of multiyear Russian investigations in the field of the development of catalysts for selective reduction of nitrogen oxides by hydrocarbons in excess oxygen, including the results obtained under international cooperative programs. Understanding of the limiting stages of the reactions and the nature of active sites responsible for activation and stabilization of reactants makes it possible to resolve deliberately the problems of controlling catalytic behavior of the systems, where transition metal cations are fixed on the surface of various supports including the supports based on partly stabilized dispersed zirconia and montmorillonite clays pillared with zirconia nanocolumns. The influence of clustering of transition metal cations and of strong cation-support interaction on the species and bond strength of the reactants involved in the key stages. Practically promising systems are identified; the experience in preparation of variously shaped monolith catalysts based on these systems is discussed.
STUDY OF THE INFLUENCE OF THE PREPARATION METHOD ON THE FORMATION OF THE PHASE COMPOSITION AND STRUCTURE OF V-Ti-O AND W-Ti-O CATALYSTS FOR SELECTIVE CATALYTIC REDUCTION OF NO BY NH3
G.V. Odegova, E.M. Slavinskaya
Kinet. Catal., 45(1) (2004) pp. 133-140.
The influence of the preparation method on the structure and phase composition of V–Ti–O and W-Ti–O catalysts for selective catalytic reduction of NO by NH3 was studied. The preparation conditions were found to insignificantly affect the structure of the resulting V–Ti–O catalysts, whereas in the case of W-Ti-O catalysts, such an influence was distinctly observed. The introduction of tungsten ions into the lattice of titanium dioxide leads to the formation of both local defects (solid solutions of the substitution type) and extended, so-called Wadsley’s defects in the framework of TiO2. The concentrations of the defects of both types depend on the catalyst preparation conditions.
SYNTHESIS OF MESOPOROUS COMPLEX FRAMEWORK ZIRCONIUM PHOSPHATES VIA ORGANIC-INORGANIC NANOCOMPOSITES: GENESIS OF STRUCTURE, ADSORPTION AND CATALYTIC PROPERTIES
Yu.V. Frolova, V.A. Sadykov, S.N. Pavlova, S.A. Veniaminov, R.V. Bunina, E.B. Burgina, V.N. Kolomiichuk, T.V. Larina, N.V. Mezentseva, M.A. Fedotov, A.M. Volodin, E.A. Paukshtis, V.B. Fenelonov, R. Roy*, D. Agrawal* (*Materials Research Laboratory, Pennsylvania State University, University Park, PA, USA)
Mat. Res. Soc. Symp. Proc., 788 (2004) pp. 215-220.
This work presents the first results of synthesis of framework binary phosphates of zirconium and transition metal cations (Co, Cu, Ce) via nanocomposites of starting inorganic salts with citric acid and studies of their structure genesis. Nanoparticles of layered Zr phosphates with typical sizes in the range of 18-24 Ǻ are formed at the mixing stage. Less basic Cu and Co cations are mainly octacoordinated with both phosphate groups of those nanoparticles and citric acid molecules. At subsequent thermal treatment, Cu and Co cations are incorporated within Zr phosphate nanoparticles acquiring a low coordination approaching a tetrahedral one while rearranging the nuclei structure into that of a framework type. Removal of citric acid by heating under air at 200-300°C preserves the size of nanoparticles while their ordered stacking forms mesoporous structure with a narrow pore size distribution ~ 50 Å and specific surface area up to 200 m2/g after calcination at 600°C. The binary phosphates promoted by a small amount of Pt were found to be effective catalysts of NOx selective reduction by decane in the oxygen excess not subjected to coking with a high and stable performance at high space velocities in the presence of steam.
EXPERIMENTAL AND THEORETICAL STUDIES OF THE ELECTRONIC SPECTRA OF MIXED FRAMEWORK PHOSPHATES OF Zr AND Co
Yu.V. Frolova, V.I. Avdeev, S.Ph. Ruzankin, G.M. Zhidomirov, M.A. Fedotov, V.A. Sadykov
J. Phys. Chem. B, 108(22) (2004) pp. 6969-6980.
Electronic Diffuse Reflectance Spectra were acquired for samples of mixed framework phosphates of zirconium and cobalt calcined in a broad temperature range (40-900°C). Analysis of the spectral features and their comparison with available data for different cobalt phosphates and CoAPO revealed that in complex framework phosphates the nearest coordination sphere of Co cations mainly corresponds to the oxygen polyhedra with a low coordination number such as tetrahedron, pyramid etc. In the frames of the time-dependent DFT method (TDDFT), the electronic excitation energies for cobalt cations in different oxygen environment have been calculated. The obtained results allowed to describe the spectra of mixed cobalt-zirconium phosphates of various crystallinity both in the d-d transition and charge transfer ranges with a due regard for simultaneous presence of Co cations in different coordination polyhedrons and spin states. In prediction of the spectral features, the approach used in this work was shown to reasonably agree with the traditional concepts and experience in analysis of the electronic spectra of transition metal cations in their complexes and inorganic frameworks.
PREPARATION AND MICROSTRUCTURAL AND TEXTURAL CHARACTERIZATION OF SINGLE-PHASE ALUMINUM OXIDES
E.V. Kulko, A.S. Ivanova, G.S. Litvak, G.N. Kryukova, S.V. Tsybulya
Kinet. Catal., 45(5) (2004) pp. 714-721.
Conditions for the preparation of single-phase θ-, η-, and χ-aluminas were determined. The structures of η- and χ-aluminas were characterized. With the use of high-resolution electron microscopy, it was found that η-Al2O3 particles exhibited the most developed {111} face and consisted of coherently joined domains with a pronounced platelet shape. Planar defects in the (111) plane occurred in the η-Al2O3 particles. Microstructural differences between single-phase η-Al2O3 and ν-Al2O3 with a defect spinel structure were revealed. It was found that the η-Al2O3, χ-Al2O3, and θ-Al2O3 oxides are characterized by uniformly porous structures with average pore diameters of 47, 55, and 110 Å, respectively.
THE EFFECT OF MODIFICATION ON THE STRUCTURAL, ACIDIC, AND CATALYTIC PROPERTIES OF A LAYERED ALUMINOSILICATE
S.Ts. Khankhasaeva*, S.V. Badmaeva*, E.Ts. Dashinamzhilova*, M.N. Timofeeva, E.B. Burgina, A.A. Budneva, E.A. Paukshtis (*Baikal Institute of Nature Management, Ulan-Ude, Russia)
Kinet. Catal., 45(5) (2004) pp. 708-713.
The effect of modification on the structural, acidic, and catalytic properties of a natural layered aluminosilicate containing 90% montmorillonite was studied. With the use of low-temperature nitrogen adsorption and XRD analysis, it was found that the addition of hydroxo complexes of aluminum prevents the silicate layers of the layered aluminosilicate from closing upon heating and results both in the formation of stable micropores and in a considerable increase in the specific surface area. The acidic properties of the H, Na, and Al forms of the layered aluminosilicate were studied by IR spectroscopy of adsorbed CO molecules and by the indicator method. After modification with hydroxo complexes of aluminum, the number of Lewis acid sites and the accessibility of acidic OH groups to CO adsorption increased. The total number and strength of acid sites increased as the calcination temperature of the layered aluminosilicate was increased. A correlation between catalytic activity in the reaction of acetone dimerization and the number of acid sites in different forms of the layered aluminosilicate was obtained.
PROPERTIES OF THE SOL-GEL TiO2-SiO2 SELECTIVE OXIDATION CATALYSTS PREPARED USING ETHYL SILICATE 40 AS A SILICA PRECURSOR
J. Mrowiec-Białoń*, A.B. Jarzębski*, O.A. Kholdeeva, N.N. Trukhan, V.I.Zaikovskii, V.V. Kriventsov, Z. Olejniczak* (*Institute of Chemical Engineering, Gliwice, Poland)
Appl. Catal. A, 273(1-2) (2004) pp. 47-53.
It has been shown that the effective titania-silica sol-gel catalysts can be obtained from a modified version of the two-stage, acid-base sol-gel procedure with tetraethoxysilane (TEOS) and ethyl silicate 40 used as silica precursors in the first and second step, respectively. Porous texture of these materials appeared to be similar or superior to those of the corresponding ones synthesized using TEOS or TMOS and this plus excellent surface homogeneity positively affected their catalytic properties which proved to be very attractive in the oxidation of 2,3,6-trimethylphenol (TMP) to 2,3,5-trimethyl-1,4- benziquinone (TMBQ) using aqueous H2O2.
INTRODUCTION TO PHYSICOCHEMICAL CHEMISTRY OF SUPRAMOLECULAR STRUCTURE OF ADSORBENTS AND CATALYSTS
V.B. Fenelonov
Monograph, Publishing House of SB RAS, Novosibirsk, 2004, 414 p.
The monograph is first in the available world literature which deals with physicochemical basis of a new interdisciplinary scientific area, namely supramolecular structures (textures) of porous materials, the mechanisms of their formation and application of adsorption methods for their characterization. Here, the term supramolecular relates to the structures with elements of no less then one nanometer in size (without top size limits). These structures differ in many features from objects of molecular chemistry because such elements as surface curvature, topological element connectivity, morphology are the key elements here. Weaker and less specific forces (Van der Waals and electrostatic forces) of intermolecular interaction substitute for the forces of covalent intramolecular interaction. The monograph will be useful to specialists who work in the fields of synthesis, characterization or application of porous and dispersed materials (from biologists to geologists) including, naturally, specialists in heterogeneous catalysis and adsorption.
FORMATION OF Ru-M/SIBUNIT CATALYSTS FOR AMMONIA SYNTHESIS
N.B. Shitova, N.M. Dobrynkin, A.S. Noskov, I.P. Prosvirin, V.I. Bukhtiyarov, D.I. Kochubey, P.G. Tsyrulnikov, D.A. Shlyapin
Kinet. Catal., 45(3) (2004) pp. 414-421.
The effects of the nature of ruthenium and alkaline promoter precursor compounds and support properties on the activity of Ru–(Cs, K)/Sibunit catalysts in the reaction of ammonia synthesis were studied. The formation of active centers in the catalysts was studied with the use of EXAFS, XPS, and electron microscopy. It was found that ruthenium and a portion of cesium occurred in metallic states in the reduced catalysts. The most active catalysts containing 4 wt % ruthenium at the atomic ratios [K] : [Ru] = 4.5 and [Cs] : [Ru] = 2.5 were obtained with the use of the [Ru(dipy)3](OH)2 complex.
NEW Y(La)–M–O BINARY SYSTEMS (M = Ca, Sr, or Ba): SYNTHESIS, PHYSICOCHEMICAL CHARACTERIZATION, AND APPLICATION AS THE SUPPORTS OF RUTHENIUM CATALYSTS FOR AMMONIA SYNTHESIS
A.S. Ivanova, E.S. Kalyuzhnaya*, G.S. Litvak, E.M. Moroz, S.M. Yunusov*, V.S. Lenenko*, B.L. Moroz, V.B. Shur*, V.A. Likholobov (*Nesmeyanov Institute of Organoelement Compounds, Moscow, Russia)
Kinet. Catal., 45(4) (2004) pp. 541-546.
The effect of the nature of the alkaline-earth metal on the phase composition and specific surface area of new Y(La)–M–O binary oxide compositions (M = Ca, Sr, or Ba) prepared by coprecipitation was studied. These systems were found to contain mixed compounds (M2Y2O5, MY2O4, and MLa2O4), which are different in thermal stability, in addition to individual La2O3 or Y2O3 phases. The Y(La)–M–O compositions calcined at 450°C were characterized by a more developed specific surface area, as compared with that of individualLa2O3or Y2O3. An increase in the calcination temperature to 650°C was accompanied by a decrease in the specific surface area of binary compositions. Catalysts prepared by supporting K2[Ru4(CO)13] onto the Y(La)–M–O systems were active in ammonia synthesis at 250-400°C and atmospheric pressure. The most active of these catalysts, K2[Ru4(CO)13]/Y–Ba–O, provided a higher yield of NH3 at 250-300°C than analogous catalysts prepared with the use of well-known supports (Sibunit, CFC-1, and C/MgO).
SELECTIVE CATALYTIC OXIDATION OF METHANE TO SYNGAS OVER SUPPORTED MIXED OXIDES CONTAINING Ni AND Pt
S.N. Pavlova, N.N. Sazonova, V.A. Sadykov, O.I. Snegurenko, V.A. Rogov, E.M. Moroz, I.A. Zolotarskii, A.V. Simakov, V.N. Parmon
Kinet. Catal., 45(4) (2004) pp. 589-597.
The activity of Ni, Pt, and LaNiO3 supported on α-Al2O3 is studied in the selective catalytic oxidation of methane to syngas at 900°C and a contact time of ~0.002 s using dilute mixtures (1000 ppm CH4 +500 ppm O2 in He). The grain size was ~100 μm. The method of X-ray phase analysis shows that supported LaNiO3, both pure and containing Pt, has a perovskite hexagonal structure with altered lattice parameters. Using temperature-programmed reduction by hydrogen, it was found that the reduction of supported LaNiO3 is simplified in the presence of Pt and/or Ce0.2Zr0.8O2. The activity and selectivity of the catalysts in the reaction of selective catalytic oxidation of methane depends on their composition and oxidative–reductive treatment. It was found that, in the presence of catalysts based on LaNiO3 and containing Pt and/or Ce0.2Zr0.8O2, the reaction occurs with an induction period. It was assumed that the value of the induction period depends both on the dynamics of phase LaNiO3 reduction to Ni, which is associated with the accumulation of carbonate complexes and surface hydroxylation, and on slow changes in the defect structure of Ce0.2Zr0.8O2, which are associated with oxidation–reduction.
SELECTIVE METHANE OXIDATION INTO SYN-GAS AT SHORT CONTACT TIMES OVER MONOLITH CATALYSTS
S.N. Pavlova, V.A. Sadykov, I.I. Bobrova, N.F. Saputina, O.I. Snegurenko, R.V. Bunina, A.N. Salanov, V.A. Kuzmin, Z.Yu. Vostrikov, I.A. Zolotarskii
Catal. Ind., Special issue (2004) pp. 12-17.
Catalysts based on CexZr1–xO2 solid solutions promoted by Pt and Rh and applied on corundum honeycombs of cellular structure were investigated in the reaction of selective catalytic oxidation (SCO) of methane into synthesis gas. The effect of preparation method and catalyst composition, thickness of catalytic layer on activity of catalysts in SCO reaction including that in the presence of water vapors and CO2 (automatic mode), reactions of vapor and carbondioxide conversion of methane (isothermal mode) has been investigated. The produced catalysts are shown to provide CH4 conversion and selectivity to synthesis gas more than 90 % in SCO reaction at contact times τ ∼ 0,1 s, and they are of high activity in reactions of vapor and carbon-dioxide methane conversion. Introduction of CexZr1–xO2 into catalysts helps prevent carbonization and allows replacing rhodium by more inexpensive platinum. Variation of the composition of starting reaction mixture makes it possible to produce synthesis gas of different H2/CO ratios. Pilot tests of honeycomb catalysts showed that conduction of SCO in the automatic mode in the reaction mixture of composition 25−30 vol. % CH4 in the air at Tinlet = 400°C and τ = 0,1÷ 0,25 s provides methane conversion ∼ 90 % and synthesis gas output ∼50 vol. %.
PARTIAL OXIDATION OF METHANE TO SYNTHESIS GAS OVER SUPPORTED CATALYSTS BASED ON Pt-PROMOTED MIXED OXIDES
S.N. Pavlova, N.N. Sazonova, J.A. Ivanova, V.A. Sadykov, O.I. Snegurenko, V.A. Rogov, I.A. Zolotarskii, E.M. Moroz
Catal. Today, 91-92 (2004) pp. 299-303.
Alumina supported catalysts comprised of a ceria–zirconia solid solution and lanthanum nickelate promoted by Pt were tested in the partial oxidation of methane into synthesis gas under conditions (high temperature, short contact time, highly diluted gas mixture, small catalyst grains) providing acquisition of a catalyst intrinsic activity. The phase composition and reducibility of catalysts were characterized with XRD and TPR. The influence of the catalyst chemical composition, type of redox pretreatment and support phase composition on the activity has been studied. Prolonged relaxations of catalytic activity have been observed, and their nature is discussed taking into account the catalyst properties.
MONOLITH COMPOSITE CATALYSTS BASED ON CERAMOMETALS FOR PARTIAL OXIDATION OF HYDROCARBONS TO SYNTHESIS GAS
S.N. Pavlova, S.F. Tikhov, V.A. Sadykov, Yu.N. Dyatlova, O.I. Snegurenko, V.A. Rogov, Z.Yu. Vostrikov, I.A. Zolotarskii, V.A. Kuzmin, S.V. Tsybulya
Stud. Surf. Sci. Catal., 147 (2004) pp. 223-228.
Microchannel ceramometal monoliths of a high thermal and mechanical stability have been synthesized via hydrothermal treatment of powdered mixtures containing aluminum and additives (oxides or/and Ni-Cr(Co) alloy) followed by calcination. The phase composition and textural properties of monoliths depend on the additive nature affecting the aluminum reactivity toward oxidation as well as their interaction with remaining Al0. Microchannel ceramometal monoliths and catalysts based on them ensure a high performance and stability in CPO of hydrocarbons at short contact times.
CERIA-BASED FLUORITE-LIKE OXIDE SOLID SOLUTIONS AS CATALYSTS OF METHANE SELECTIVE OXIDATION INTO SYNGAS BY THE LATTICE OXYGEN: SYNTHESIS, CHARACTERIZATION AND PERFORMANCE
V.A. Sadykov, T.G. Kuznetsova, G.M. Alikina, Yu.V. Frolova, A.I. Lukashevich, Yu.V. Potapova, V.S. Muzykantov, V.A. Rogov, V.V. Kriventsov, D.I. Kochubey, E.M. Moroz, D.A. Zyuzin, V.I. Zaikovskii, V.N. Kolomiichuk, E.A. Paukshtis, E.B. Burgina, V.V. Zyryanov, N.F. Uvarov*, S. Neophytides**, E. Kemnitz*** (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia; **Institute of Chemical Engineering and High Temperature Chemical Processes, Patras, Greece; ***Institute of Chemistry, Humboldt-University, Berlin, Germany)
Catal. Today, 93-95 (2004) pp. 45-43.
Polymerized precursor route [M.P. Pechini, US Patent 3, 330 (1967) 697] was applied for synthesis of dispersed ceria-based solid solutions Ce1−xMex3+O3−y (Me3+= Sm3+ or Bi 3+, x up to 0.5). The surface properties of those samples were modified by supporting Pt. Their bulk and surface structural features were characterized by using XRD, TEM, EXAFS, X-ray wide angle scattering (RED), UV–vis, Raman, FTIRS of lattice modes and adsorbed CO. To elucidate factors controlling the surface/bulk oxygen mobility and reactivity, these results were compared with the data of the oxygen isotope exchange and/or H2/CH4 temperature-programmed reduction (TPR). Single-phase fluorite-like solid solutions with a nanodomain microstructure are characterized by distortion of the coordination polyhedra caused by dopants followed by the lattice local rearrangement into that of a lower symmetry at a high dopant content. The highest performance in methane selective oxidation into syngas by the lattice oxygen is found for samples where isolated oxygen vacancies dominate. Earlier studied Pt/Ce–Zr–La–O system has a lower oxygen mobility, is less stable in redox cycles and less selective for syngas. Bi–Ce–O system mainly combusts methane and is irreversibly decomposed by deep reduction due to metallic Bi evaporation.
METHANE SELECTIVE OXIDATION INTO SYNGAS BY THE LATTICE OXYGEN OF CERIA-BASED SOLID ELECTROLYTES PROMOTED BY Pt
V.A. Sadykov, V.V. Lunin*, T.G. Kuznetsova, G.M. Alikina, Yu.V. Frolova, A.I. Lukashevich, Yu.V. Potapova, V.S. Muzykantov, S.A. Veniaminov, V.A. Rogov, V.V. Kriventsov, D.I. Kochubey, E.M. Moroz, D.A. Zyuzin, V.I. Zaikovskii, V.N. Kolomiichuk, E.A. Paukshtis, E.B. Burgina, V.V. Zyryanov**, N.F. Uvarov**, S. Neophytides***, E. Kemnitz**** (*Moscow Lomonosov State University, Moscow, Russia; **Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia; ***Institute of Chemical Engineering and High Temperature Chemical Processes, Patras, Greece; ****Institute of Chemistry, Humboldt-University, Berlin, Germany)
Stud. Surf. Sci. Catal., 147 (2004) pp. 241-246.
Nanocomposites based upon ceria doped by Zr, Zr+La or Sm with supported Pt nanoparticles efficiently convert methane into syngas by their lattice oxygen. In red-ox cycles with pure methane as reagent, the surface carbon build-up is observed, which is lower for Sm-doped samples possessing a higher surface and lattice oxygen mobility. When stoichiometric amounts of CO2 or H2O are present in the feed, the catalysts efficiently operate in methane steam and dry reforming at high space velocities without deactivation.
METHANE TRANSFORMATION INTO SYNGAS OVER Ce–Zr–O SYSTEMS: ROLE OF THE SURFACE/BULK PROMOTERS AND OXYGEN MOBILITY
T.G. Kuznetsova, V.A. Sadykov, S.A. Veniaminov, G.M. Alikina, E.M. Moroz, V.A. Rogov, O.N. Martyanov, V.F. Yudanov, I.S. Abornev, S. Neophytides* (*Institute of Chemical Engineering and High Temperature Chemical Processes, Patras, Greece)
Catal. Today, 91-92 (2004) pp. 161-164.
The surface and bulk oxygen mobility and reactivity of ceria-based solid solutions as related to the process of methane conversion into syngas can be tuned in a broad limits by bulk and surface promoters. Variation of the surface/bulk real structure of those complex oxides and their strong interaction with the surface promoters (Pt, Ni) appear to be responsible for those effects.
REACTIVITY OF SURFACE AND BULK OXYGEN IN La1-xCaxFeO3-y SYSTEM WITH RESPECT TO METHANE OXIDATION
V.A. Sadykov, L.A. Isupova, I.S. Yakovleva, G.M. Alikina, A.I. Lukashevich, S. Neophytides* (*Institute of Chemical Engineering and High Temperature Chemical Processes, Patras, Greece)
React. Kinet. Catal. Lett., 81(2) (2004) pp. 393-398.
The reactivity and mobility of the surface and lattice oxygen in a La1-xCaxFeO3-y system prepared via a ceramic route were studied by using CH4-TPR. While the middle-temperature (400-700oC) oxygen lattice mobility reaches maximum for samples with disordered anion vacancies, the high-temperature lattice oxygen flux appears to be controlled by a rapid transfer along disordered domain walls. In the hightemperature range, a high selectivity to syngas of methane oxidation by the lattice oxygen was achieved both for pure lanthanum ferrite and for samples with a microdomain structure.
THE FIRST ISOLATED ACTIVE TITANIUM PEROXO COMPLEX: SYNTHESIS, CHARACTERIZATION AND THEORETICAL STUDY
O.A. Kholdeeva, T.A. Trubitsina, R.I. Maksimovskaya, A.V. Golovin, W.A. Neiwert*, B.A. Kolesov**, X. López***, J.-M. Poblet*** (*Department of Chemistry, Emory University, Atlanta, USA; **Institute of Inorganic Chemistry, Novosibirsk, Russia; ***Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Tarragona, Spain)
Inorg. Chem., 43(7) (2004) pp. 2284-2292.
The protonated titanium peroxo complex, [Bu4N]4[HPTi(O2)W11O39] (1), has been first prepared via interaction of the μ-oxo dimeric heteropolytungstate [Bu4N]8[(PTiW11O39)2O] with an excess of 30% aqueous H2O2 in MeCN. Peroxo complex 1 has been characterized by using elemental analysis, UV-vis, IR, resonance Raman (RR), 31P and 183W NMR spectroscopy, cyclic voltammetry, and potentiometric titration. The electronic and vibrational spectra of 1 are very similar to those of the wellknown unprotonated titanium peroxo complex [Bu4N]5[PTi(O2)W11O39] (2), while 31P and 183W NMR spectra differ significantly. A compilation of the physico-chemical techniques supports a monomeric Keggin type structure of 1 bearing one peroxo ligand attached to Ti(IV) in a η2-coordination mode. The protonation of the titanium peroxo complex results in an increase of the redox potential of the peroxo group, E1/2 = 1.25 and 0.88 V relative to Ag/AgCl reference electrode for 1 and 2, respectively. In contrast to 2, 1 readily reacts with 2,3,6-trimethylphenol (TMP) at 40°C in MeCN to give 2,2´,3,3´,5,5´-hexamethyl-4,4´- biphenol (BP) and 2,3,5-trimethyl-p-benzoquinone (TMBQ). The proportion between BP and TMBQ in the reaction products depends on the TMP/1 ratio. When a 2-fold excess of TMP is used, the main reaction product is BP (90%), while using a 2-fold excess of 1 leads to TMBQ (95%). Based on the product study, a homolytic oxidation mechanism that implicates the formation of phenoxyl radicals is suggested. The RR deuterium labeling experiments show that the activating proton is most likely localized at a Ti–O–W bridging oxygen rather than at the peroxo group. Theoretical calculations carried out at the DFT level on the protonated and unprotonated titanium peroxo derivatives also propose that the most stable complex is formed preferentially after protonation of the Ti–O–W site, however, both Ti–OH–W and TiOO–H protonated anions could coexist in solution.
AEROBIC FORMALDEHYDE OXIDATION UNDER MILD CONDITIONS MEDIATED BY Ce-CONTAINING POLYOXOMETALATES
O.A. Kholdeeva, M.N. Timofeeva, G.M. Maksimov, R.I. Maksimovskaya, A.A. Rodionova, C.L. Hill* (Department of Chemistry, Emory University, Atlanta, USA)
In “Catalysis of Organic Reactions”, Ed. J.R. Sowa, Marcel Dekker, NY, 2004.
Various Ce-POMs have been synthesized and evaluated as catalysts for the aerobic oxidation of formaldehyde at ambient conditions along with simple Ce-compounds. The most active catalyst was the monosodium acid salt of the Ce(IV)-monosubstituted silicotungstate, NaH3SiW11CeO39·7H2O (1). Optimization of the reaction conditions led to a system that afforded 30 turnovers of 1 after 5 h. Based on both IR and UV-vis, the Ce-POM retains its structure under the turnover conditions. The formic acid product inhibits the reaction. The kinetic data obtained are consistent with a chain radical mechanism of oxidation. POM 1 can be heterogenized on NH2-functionalized supports such as xerogels, fibers, etc., and in this form used repeatedly without significant loss of catalytic activity.
Co-CONTAINING POLYOXOMETALATEBASED HETEROGENEOUS CATALYSIS FOR THE SELECTIVE AEROBIC OXIDATION OF ALDEHYDES UNDER AMBIENT CONDITIONS
O.A. Kholdeeva, M.P. Vanina, M.N. Timofeeva, R.I. Maksimovskaya, T.A. Trubitsina, M.S. Melgunov, E.B. Burgina, J. Mrowiec-Białoń*, A.B. Jarzębski*, C.L. Hill** (*Institute of Chemical Engineering, Gliwice, Poland; **Department of Chemistry, Emory University, Atlanta, USA)
J. Catal., 226(2) (2004) pp. 363-371.
Tetra-n-butylammonium (TBA) salts of the cobalt-monosubstituted Keggin polyoxometalate (Co-POM), TBA4HPW11CoO39 (I) and TBA5PW11CoO39 (II), have been prepared and characterized by using elemental analysis, potentiometric titration, IR, UV–vis, 31P NMR, and cyclic voltammetry. Different modes of heterogenization of the Co-POM, including anchoring to both NH2- and NH3-modified mesoporous silica surfaces and sol–gel synthesis, have been performed. The resulting solid catalysts were characterized by N2-adsorption measurements, elemental analysis, DR-UV–vis, and FT-IR spectroscopy. The activity of the solid Co-POM materials to catalyze aerobic oxidation of two representative aldehydes, isobutyraldehyde (IBA) in MeCN and formaldehyde in H2O under mild conditions (20–400C, 1 atm of air), was assessed and compared with the catalytic activity of the corresponding homogeneous Co-POMs. An emphasis has been placed on leaching tests and catalyst recycling. The effect of protonation of the amine-modified silica surface or the Co-POM on the loading, stability, and activity of the Co-POM solid catalyst was evaluated.
2,6-DIMETHYL-γ-PYRONE AS A 13C NMR INDICATOR FOR ESTIMATING THE ACIDITY OF HETEROPOLYACID SOLUTIONS
G.M. Maksimov, A.V. Golovin
Russ. J. Inorg. Chem., 49(8) (2004) pp. 1256-1259.
13C NMR of solutions containing 2,6-dimethyl-γ-pyrone as a 13C NMR indicator were used to estimate the acidity of aqueous solutions of ordinary acids (HCl, HNO3, HClO4) and heteropolyacids (HPA) (13HPA of five structural types were used). In the concentration range [H+] = 0–1.7 mol/l, the change in the signal positions in the spectra reaches 10 ppm, which enables the use of this method to compare the solution acidities of ordinary acids. In HPA solutions, indicator–HPA anion and, probably, indicator–H+–HPA anion interactions were detected. It was concluded that the indicator method is inapplicable for acidity determinations in HPA solutions.
HYDROFORMYLATION OF 1-HEXENE CATALYZED BY WATER SOLUBLE CoCl2(TPPTS)2 IN BIPHASIC MEDIUM
D.U. Parmar*, H.C. Bajaj*, R.V. Jasra*, B.L. Moroz, V.A. Likholobov (*Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute, Gujarat, India)
J. Mol. Catal. A: Chem., 211(1-2) (2004) pp. 83-87.
CoCl2(TPPTS)2 catalyzed hydroformylation of 1-hexene was studied in an aqueous biphasic medium. The effect of temperature, pressure, and concentration of cobalt catalyst on the reaction was studied. At elevated temperatures and pressures, it gave >90% conversion with 68% selectivity for aldehyde and n/iso ratio of 3.0 for the aldehyde.
SOLID SUPERACIDS FOR HALIDE-FREE CARBONYLATION OF DIMETHYL ETHER TO METHYL ACETATE
G.G. Volkova, L.M. Plyasova, L.N. Shkuratova, A.A. Budneva, E.A. Paukshtis, M.N. Timofeeva, V.A. Likholobov
Stud. Surf. Sci. Catal., 147 (2004) pp. 403-408.
The production of methyl acetate directly from dimethyl ether was performed by halide-free carbonylation. The solid superacid catalysts with high density of Brønsted acid sites Rh/CsxH3-xPW12O40 were compared with Rh/SO4/ZrO2 and Rh/WOx/ZrO2. The correlation between the nature of acid sites and activity and selectivity of the catalysts in halide-free carbonylation of DME was found.
PREPARATION OF COLLOIDAL SOLUTIONS OF NOBLE METALS STABILIZED BY POLYOXOMETALATES AND SUPPORTED CATALYSTS BASED ON THESE SOLUTIONS
G.M. Maksimov, A.L. Chuvilin, E.M. Moroz, V.A. Likholobov, K.I. Matveev
Kinet. Catal., 45(6) (2004) pp. 870-878.
Conditions for the preparation of stable aqueous monometallic and bimetallic colloidal solutions (sols) of noble metals (Ru, Rh, Pd, Pt, Ir, Ag, and Au) in the presence of polyoxometalates containing W, Mo, V, and Nb were found. The stability of sols against coagulation at room temperature was studied. The metal/C samples prepared by metal adsorption from sols were studied by powder X-ray diffraction analysis and transmission electron microscopy. The following factors of importance for the preparation of a stable sol are discussed: (1) the formation of a sol of a metal polyhydroxo complex stabilized by a polyoxometalate (preliminary stage) and (2) the formation of polyoxometalate–metal clusters in the course of reduction of polyhydroxo complexes.
SYNTHESIS AND CHARACTERIZATION OF THE HETEROPOLYANION SiW11CeO394–
G.M. Maksimov, R.I. Maksimovskaya, O.A. Kholdeeva
Russ. J. Inorg. Chem., 49(9) (2004) pp. 1325-1330.
The heteropolyanion [SiW11CeO39]4–I) has been synthesized in solution by electrodialysis method. It was isolated as acid sodium and cesium salts and characterized by 183W and 17O NMR and IR spectroscopy. The 183W NMR spectrum of I contains six lines. 183W and 17O NMR spectra were also recorded for [(SiW11O39)2Ce]12- (II), which had been obtained earlier. The 183W NMR spectrum of II shows 11 lines. Assignment of the 183W NMR spectra of I and II was carried out. The thermal stability of NaH3SiW11CeO39 was studied.
NEW AMMONIA SYNTHESIS CATALYSTS BASED ON SUPPORTED POTASSIUM CARBONYL RUTHENATES AS PRECURSORS OF CATALYTICALLY ACTIVE RUTHENIUM PARTICLES AND POTASSIUM PROMOTER
S.M. Yunusov*, E.S. Kalyuzhnaya*, B.L. Moroz, A.S. Ivanova, T.V. Reshetenko, L.B. Avdeeva, V.A. Likholobov, V.B. Shur* (*Nesmeyanov Institute of Organoelement Compounds, Moscow, Russia)
J. Mol. Catal. A: Chem., 219(1) (2004) pp. 149-153.
New supported single-component ruthenium catalysts for ammonia synthesis are reported. For preparation of the catalysts, various potassium carbonyl ruthenates such as K2[Ru6(CO)18] (K/Ru = 1/3), K4 [Ru4(CO)12] (K/Ru = 1/1), K6[Ru6(CO)16] (K/Ru = 1/1), K6[Ru4(CO)11] (K/Ru = 1.5/1) and K2[Ru(CO)4] (K/Ru = 2/1) were used as precursors of both catalytically active ruthenium particles and potassium promoter while graphite-like active carbon “Sibunit” was utilized as a support. The studied catalysts have been compared in their activity with the previously described shanson-e.tk(CO)13]-based catalyst (K/Ru = 1/2) on “Sibunit” carbon. It has been established that the rate of the ammonia synthesis at 300ºC over these catalysts increases with the increase in the K:Ru ratio in the starting carbonyl metallate, reaching a maximum in the case of the K6[Ru4(CO)16]-based sample. On further enhancement in the K:Ru ratio, i.e. when the K2[Ru(CO)4] catalyst is used, the rate of the ammonia K2[Ru(CO)4]-based catalyst in the ammonia synthesis can be considerably augmented on the replacement of “Sibunit” by CFC-II carbon or MgO. The use of γ- Al2O3 or carbon-coated γ-Al2O3 as supports decreases the reaction rate. An introduction of metallic potassium into the K2[Ru(CO)4]catalysts on carbons “Sibunit” and CFC-II accelerates strongly the process of the ammonia synthesis. The highest activity is exhibited by the K2[Ru(CO)4] + K system on “Sibunit” at the metallic potassium to carbon molar ratio of 0.08. On using this catalyst (3.55 g), the steady ammonia concentration in the gas flow at 300ºC and 1 atm amounts to 71.1% of the equilibrium value while at 350 and 400ºC the process of the ammonia synthesis fully reaches the equilibrium. In its efficiency in the ammonia production at 250-300ºC, the K2[Ru(CO)4] + K catalyst on “Sibunit” carbon significantly exceeds the previously developed K2[Ru4(CO)13] + K catalyst on the same support.
REGENERATION OF CATALYSTS BASED ON AQUEOUS SOLUTIONS OF Mo-V PHOSPHOROUS HETEROPOLY ACIDS UNDER OXYGEN PRESSURE
E.G. Zhizhina, M.V. Simonova, V.F. Odyakov, K.I. Matveev
Chem. Sustain. Devel., 12(6) (2004) pp. 683-688.
Oxidation with oxygen of 0.2 M H7+mP(VIV)m(VV)4-mMo8O40 (HmHPA-4) at temperatures 373-433 K and O2 pressure up to 8 atm (810 kPа) was studied. Maximal reaction rate s observed at 433 K. Partially oxidized 2 M HmHPA-4 solutions are thermally unstable at higher temperatures. Apparent activation energy is increased with the increase of oxidation state.
CATALYTIC SYNTHESIS OF 1,4-NAPHTHOAND 9,10-ANTHRAQUINONES BY REACTION OF DIENE SYNTHESIS FOR PULP AND PAPER INDUSTRY
E.G. Zhizhina, K.I. Matveev, V.V. Russkikh* (*Vorozhtsov Novosibirsk Institute of Organic Chemistry, Novosibirsk, Russia)
Chem. Sustain. Devel., 12(1) (2004) pp. 47-51.
Adducts of the diene synthesis of 1,4-benzo- and 1,4-naphthoquinones with butadiene are established to be oxidized to 1,4-naphtho- and 9,10-anthraquinones under the action of Mo-V-P heteropolyacids (HPA) and salts of these acids. Prospectively, the multistage catalytic synthesis of 1,4-quinones can be reduced to one stage in the presence of HPA.
REACTIONS OF NITROSOARENES CONTAINING ELECTRON-WITHDRAWING SUBSTITUENTS WITH COORDINATED CO. SYNTHESIS AND STRUCTURE OF COMPLEXES Pd2(OAc)2(p-ClC6H4N[p-ClC6H3NO])2 AND Pd2(OAc)2(о-ClC6H4N[о-ClC6H3NO])2
S.T. Orlova*, T.A. Stromnova*, D.N. Kazyul´kin*, L.I. Boganova*, D.I. Kochubey, B.N. Novgorodov (*Kurnakov Institute of General and Inorganic Chemistry, Moscow, Russia)
Russ. Chem. Bull., 53(4) (2004) pp. 819-824.
The reaction of tetranuclear Pd4(μ-COOCH3)4(μ-CO)4 cluster (1a) with p- and o-chloronitrosobenzenes was found to give dinuclear nitrosoamide complexes, Pd2(OAc)2(p-ClC6H4N[p-ClC6H3NO])2 (4) and Pd2(OAc)2(о-ClC6H4N[о-ClC6H3NO])2 (5), respectively. The formation of complexes 4 and 5 is accompanied by evolution of CO2, resulting from oxidation of CO coordinated in cluster 1. Complexes 4 and 5 were characterized by elemental analysis and IR and 1H NMR spectroscopy; their structures were studied by EXAFS. The reactions of dinuclear complex 4 with molecular hydrogen and CO were studied. The major products of reduction of 4 with hydrogen include metallic palladium, acetic acid, cyclohexanone, and molecular nitrogen. Treatment of complex 4 with CO under mild conditions (1 atm, 20°C) affords p-chlorophenyl isocyanate.
CHEMICAL REACTIONS IN TROPOSPHERE
V.S. Zakharenko, A.N. Moseichuk* (*Institute of Petrochemistry, Toms, Russia)
Ocean Atmosph. Optics, 16(5-6) (2003) pp. 447-453.
Primary gas-phase chemical reactions initiated by tropospheric solar irradiation are briefly overviewed. The work also encompasses the survey of investigations in the field of photo-induced heterogeneous chemical processes that proceed on the surface of basic phase components of tropospheric aerosols. The processes are suggested to divide into groups with different types of absorption of the irradiation quanta. Based on the division, the experimentally observed processes can be identified and classified as photoadsorption, photocatalytic reactions, interaction of gas-phase molecules with a solid surface under the action of irradiation quanta, and surface photochemical reactions.
HETEROGENEOUS CATALYSIS IN THE FENTON-TYPE SYSTEM FeZSM-5/H2O2
E.V. Kuznetsova, E.N. Savinov, L.A. Vostrikova, V.N. Parmon
Appl. Catal. B, 51(3) (2004) pp. 165-170.
The work deals with Fe-containing zeolites for the catalytic oxidation of water-dissolved organic substances by H2O2. A detailed study of the system FeZSM-5/H2O2 meant to reveal the nature of the catalysis is presented. For this purpose, the following characteristics of the system were determined: the iron concentration in the filtrate of the catalyst suspension in several reaction runs; Fe content changes in the repeatedly used heterogeneous catalyst; the catalytic activities of the filtrate and of the heterogeneous catalyst in several runs. It has been shown that in the system FeZSM-5/H2O2, the heterogeneous catalysis makes the main contribution to the catalyst activity in the H2O2 decomposition and oxidation of organic substrates. Additionally, in the presence of the iron ions complexing agents, FeZSM-5 showed a significantly different behavior in comparison to the homogeneously dissolved iron cations. For example, in the presence of the P2O74− anions, the rate of the H2O2 decomposition increased by several times in the FeZSM-5 suspension, while it is totally reduced in a homogeneous iron solution.
THE CATALYTIC AND PHOTOCATALYTIC OXIDATION OF ORGANIC SUBSTANCES USING HETEROGENEOUS FENTON-TYPE CATALYST
E.V. Kuznetsova, E.N. Savinov, L.A. Vostrikova, G.V. Echevsky
Wat. Sci. Technol., 49(4) (2004) pp. 109-115.
This paper deals with catalytic and photocatalytic oxidation of organic substances using H2O2 over heterogeneous Fenton-type catalysts. In the study a series of Fe-containing catalysts was experienced. A zeolite named as FeZSM-5 was selected as the most active heterogeneous Fenton-type catalyst. The FeZSM-5 reported was prepared by hydrothermal crystallization in the presence of iron salt. In contrast to the homogeneous Fenton system the catalyst prepared had minimal, if any, leaching of iron ions, was stable during 30 catalytic runs and did not lose its activity in the presence of complexing agents, e.g. P2O7 4-. The catalyst was active in oxidation of organic substances at pH from 1.5 to 8, maximum activity was observed at pH = 3. The FeZSM-5 effectively oxidized a simulant of the warfare agent, diethylnitrophenil phosphate, which is hardly detoxified by other methods. It appeared that the rate of oxidation of formic acid, ethanol and benzene over FeZSM-5 increased under the action of visible light (λ>436 nm), quantum efficiency being 0.06-0.14.
TOCATALYTIC OXIDATION OF DIMETHYL METHYLPHOSPHONATE ON A TiO2 SURFACE
D.A. Trubitsyn, A.V. Vorontsov
Mendeleev Commun., 14(5) (2004) pp. 197-198.
The products of dimethyl methylphosphonate (DMMP) hydrolysis and photocatalytic oxidation on TiO2 were identified and quantified by a FTIR technique at different relative air humidities and concentrations of DMMP.
SELECTIVITY OF PHOTOCATALYTIC OXIDATION OF GASEOUS ETHANOL OVER PURE AND MODIFIED TiO2
A.V. Vorontsov, V.P. Dubovitskaya
J. Catal., 221(1) (2004) pp. 102-109.
The rates of the two main stages of photocatalytic ethanol destruction - oxidation of ethanol to acetaldehyde and oxidation of acetaldehyde to CO2 - were studied under varied concentrations of ethanol and acetaldehyde and photocatalyst irradiance, at different temperatures, and over different photocatalysts. The rates followed the semiempirical three sites Langmuir–Hinshelwood model that envisages sites for ethanol and acetaldehyde adsorption and additional sites for competitive adsorption of ethanol and acetaldehyde. The increase in irradiance gave rise to higher selectivity toward CO2 via increased concentrations of gaseous intermediate acetaldehyde. However, the rate of ethanol oxidation rose faster than the rate of acetaldehyde oxidation. The selectivity toward CO2 monotonically decreased with temperature over TiO2 and the rate of oxidation reached a maximum at 80°C. Among platinum-doped catalysts, the best activity was found for 1.1% Pt/TiO2. Platinum addition to TiO2 resulted in a 1.5- to 2-fold increased overall rate of oxidation. The selectivity to CO2 over Pt/TiO2 catalyst monotonically increased with temperature. Separate studies in a batch reactor demonstrated that addition of platinum changed the product distribution. Acetic acid, instead of carbon monoxide, was formed in copious quantities over the Pt/TiO2 catalyst.
PATHWAYS OF PHOTOCATALYTIC GAS PHASE DESTRUCTION OF HD SIMULANT 2-CHLOROETHYL ETHYL SULFIDE
A.V. Vorontsov, C. Lion*, E.N. Savinov, P.G. Smirniotis** (*Institut de Topologie et de Dynamique des Systèmes de I'Université Paris-7, Paris, France; **Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, USA)
J. Catal., 220(2) (2003) pp. 414-423.
Photocatalytic oxidation of HD simulant, 2-chloroethyl ethyl sulfide (CEES), was studied in a specially designed coil and flow photocatalytic reactor by means of GC-MS and FTIR techniques. TiO2 Hombikat UV 100 photocatalyst was deactivated after a few hours of operation, which was signaled by the appearance of incomplete oxidation products in the reactor effluent and accumulation of incomplete oxidation products on the TiO2 surface. Complete reactivation of the photocatalyst was achieved by washing the photocatalyst with water. Compared to diethyl sulfide, CEES showed lower reactivity in photocatalytic oxidation and was accumulated on the TiO2 surface after catalyst deactivation. Without UV irradiation, hydrolysis of CEES proceeded on the TiO2 surface. Major gaseous products of CEES incomplete photocatalytic oxidation are acetaldehyde, chloroacetaldehyde, SO2, diethyl disulfide, and chloroethylene. Surface products extracted from the TiO2 surface with acetonitrile and water include mainly 2-chloroethyl ethyl sulfoxide and ethanesulfinic and ethanesulfonic acids, as well as diethyl di-, tri-, and tetrasulfides mono and disubstituted in the β-position with a chlorine or hydroxyl group. While surface monodentate sulfates can be removed upon washing, surface bidentate species stayed on the surface and possibly contribute to the permanent catalyst deactivation.
COMPARATIVE STUDY ON PHOTOCATALYTIC OXIDATION OF FOUR ORGANOPHOSPHORUS SIMULANTS OF CHEMICAL WARFARE AGENTS IN AQUEOUS SUSPENSION OF TITANIUM DIOXIDE
E.A. Kozlova, P.G. Smirniotis*, A.V. Vorontsov (*Chemical and Materials Engineering Department, University of Cincinnati, Cincinnati, USA)
J. Photochem. Photobiol., A.,
162(2-3) (2004) pp. 503-511.Photocatalytic oxidation by oxygen of air was carried out for dimethyl methyl phosphonate (DMMP), trimethyl phosphate (TMP), triethyl phosphate (TEP), and diethyl phosphoramidate (DEPA) in different concentration. The initial rate of organophosphorus compounds consumption increases with the initial concentration at relatively low concentrations but decreases at higher initial concentrations. If the concentration is higher than the concentration in maximum, the rate decreases because of the lack of adsorbed oxygen. These summit-like dependencies are well approximated by one site Langmuir–Hinshelwood equation with competitive adsorption of oxygen and organophosphorus compound. Parameters of the Langmuir–Hinshelwood equation are reported. Complete mineralization of the organophosphorus compounds at the end of reaction was evidenced by the total organic carbon concentration profiles. These profiles have sigmoidal shape. GC–MS technique was used to identify intermediates of TEP and TMP oxidation. The main intermediates are dimethyl phosphate and methyl phosphate in the case of TMP and diethyl phosphate and ethyl phosphate in the case of TEP. The set of intermediates shows that photocatalytic oxidation proceeds primarily at α carbon atoms of TEP. The distribution of intermediates corroborates that photocatalytic oxidation is initiated by reaction with hydroxyl radicals.
INFLUENCE OF PARTICLE AGGLOMERATION ON THE CATALYTIC ACTIVITY OF CARBON-SUPPORTED Pt NANOPARTICLES IN CO MONOLAYER OXIDATION
F. Maillard*, S. Schreier*, M. Hanzlik*, E.R. Savinova , S. Weinkauf*, U. Stimming* (*Technische Universität München, Garching, Germany)
Phys. Chem. Chem. Phys., 7(2) (2005) pp. 375-383.
Fuel cell electrocatalysts usually feature high noble metal contents, and these favour particle agglomeration. In this paper a variety of synthetic approaches (wet chemical deposition, electrodeposition and electrodeposition on chemically preformed Pt nuclei) is employed to shed light on the influence of nanoparticle agglomeration on their electrocatalytic properties. Pt loading on model glassy carbon (GC) support is increased systematically from 1.8 to 10.6 μg Pt cm–2 and changes in the catalyst structure are followed by transmission electron microscopy. At low metal loadings (≤5.4 μg Pt cm–2) isolated single crystalline Pt nanoparticles are formed on the support surface by wet chemical deposition from H2PtCl4 precursor. An increase in the metal loading results, first, in a systematic increase of the average diameter of isolated Pt nanoparticles and, second, in coalescence of nanoparticles and formation of particle agglomerates. This behaviour is in line with the previous observations on carbon-supported noble metal fuel cell electrocatalysts. The catalytic activity of Pt/GC electrodes is tested in CO monolayer oxidation. In agreement with the previous studies, it was found that the reaction is strongly size sensitive, exhibiting an increase of the reaction overpotential as the particle size decreases below ca. 3 nm. At larger particle sizes the dependence levels off, the catalytic activity of particles with diameters above 3 nm approaching that of polycrystalline Pt. Meanwhile, Pt agglomerates show remarkably enhanced catalytic activity in comparison to either isolated Pt nanopraticles or polycrystalline Pt foil, catalysing CO monolayer oxidation at ca. 90 mV lower overpotential. Enhanced catalytic activity of Pt agglomerates is ascribed to high concentration of surface defects. CO stripping voltammograms from Pt/GC electrodes, comprising Pt agglomerates along with isolated single crystalline Pt nanoparticles from 2 to 6 nm size, feature double voltammetric peaks, the more negative corresponding to CO oxidation on Pt agglomerates, while the more positive to CO oxidation on isolated Pt nanoparticles. It is shown that CO stripping voltammetry provides a fingerprint of the particle size distribution and the extent of particle agglomeration in carbon-supported Pt catalysts
INFRARED SPECTROSCOPIC STUDY OF CO ADSORPTION AND ELECTRO-OXIDATION ON CARBON-SUPPORTED Pt NANOPARTICLES: INTERPARTICLE VERSUS INTRAPARTICLE HETEROGENEITY
F. Maillard*, E.R. Savinova, P.A. Simonov, V.I. Zaikovskii, U. Stimming* (*Technische Universität München, Garching, Germany)
J. Phys. Chem. B, 108(46) (2004) pp. 17893-17904.
In this paper, Fourier transform infrared (FTIR) spectroscopy and stripping voltammetry at saturation and submonolayer CO coverages is used to shed light on the influence of size on the CO adsorption and electro-oxidation on Pt nanoparticles. Pt nanoparticles supported on low surface area (~1 m2·g-1) carbon (Sibunit) are used throughout the study. The vibrational spectra of adsorbed CO are dominated by interparticle heterogeneity (contribution of particles of different size in the range from 0.5 to 5 nm) rather than intraparticle heterogeneity (contribution of different adsorption sites). CO stripping voltammetry exhibits two peaks separated by approximately 0.25 V (at 0.02 V s-1), which are attributed to the CO oxidation from "large" (~3.6 nm) and "small" (~1.7 nm) Pt nanoparticles. Using stepwise oxidation, it was possible to separate the contributions of "large" and "small" nanoparticles and obtain their infrared and voltammetric "fingerprints". Considerable differences are observed between "large" and "small" nanoparticles in terms of (i) the vibrational frequencies of adsorbed CO molecules (ii) their vibrational coupling, and (iii) CO oxidation overpotential.
SIZE EFFECTS ON REACTIVITY OF Pt NANOPARTICLES IN CO MONOLAYER OXIDATION: THE ROLE OF SURFACE MOBILITY
F. Maillard*, M. Eikerling*, O.V. Cherstiouk, S. Schreier*, E.R. Savinova, U. Stimming* (*Technische Universität München, Garching, Germany)
Faraday Discuss., 125 (2004) pp. 357-377.
The reactivity of model Pt nanoparticles supported on glassy carbon has been studied. The particle size effect is rationalized for CO monolayer oxidation exploring electrochemical methods (stripping voltammetry and chronoamperometry) and modelling. Significant size effects are observed in the particle size interval from ca. 1 to 4 nm, including the positive shift of the CO stripping peak with decreasing particle size and a pronounced asymmetry of the current transients at constant potential. The latter go through a maximum at low COads conversion and exhibit tailing, which is the longer the smaller the particle size. Neither mean field nor nucleation & growth models give a coherent explanation of these experimental findings. It was, therefore, suggested a basic model employing the active site concept. With a number of reasonable simplifications a full analytical solution is obtained, which allows a straightforward comparison of the theory with the experimental data. A good correspondence between experiment and theory is demonstrated. The model suggests restricted COads mobility at Pt nanoparticles below ca. 2 nm size, with the diffusion coefficient strongly dependent on the particle size, and indicates a transition towards fast diffusion when the particle size exceeds ca. 3 nm. Estimates of relevant kinetic parameters, including diffusion coefficient, reaction constant etc. are obtained and compared to the literature data for extended Pt surfaces.
POISONING OF PtRu/C CATALYSTS IN THE ANODE OF A DIRECT METHANOL FUEL CELL: A DEMS STUDY
T. Seiler*, E.R. Savinova, K.A. Friedrich*,**, U. Stimming* (*Technische Universität München, Garching, Germany; **Center for Solar Energy and Hydrogen Research Baden-Würtenberg, Ulm, Germany)
Electrochim. Acta, 49(22-23) (2004) pp. 3927-3936.
Poisoning of a commercial PtRu/C electrocatalyst with the products of methanol dehydrogenative adsorption has been studied in a membrane electrode assembly of a liquid fed direct methanol fuel cell at different electrode potentials in the temperature range between 30 and 110°C using a newly designed DEMS setup. In all cases COads is identified as the stable methanol dehydrogenation product. The adsorbate coverage versus the electrode potential follows a bellshaped curve, reaching a maximum around 0.1/0.2 V RHE. During methanol oxidation, the adsorbate coverage remains high and increases with temperature (θ ~ 0.6 at 90°C in 1 M methanol solution). Kinetics of methanol adsorption has been studied at the open circuit potential (between 0 and 20 mV versus RHE). The coverage of the adsorbate and the rate of adsorption rise with temperature. The adsorption isotherms are of Temkin type with an adsorption rate constant kad increasing from 1.6 ± 0.1 cm3 mol−1 s−1 at 30°C to 73 ± 11 cm3 mol−1 s−1 at 110°C and a temperature-dependent inhomogeneity parameter αf ranging from 35 ± 1 at 30°C to 8.3 ± 0.2 at 110°C. The apparent activation energy of methanol adsorption at the OCP and zero coverage is estimated as ca. 45 ± 2 kJ mol−1.
HYDROXIDE ADSORPTION ON Ag(110) ELECTRODES: AN IN SITU SECOND HARMONIC GENERATION AND EX SITU ELECTRON DIFFRACTION STUDY
S.L. Horswell*, A.L.N. Pinheiro*, E.R. Savinova, B. Pettinger*, M.-S. Zei*, G. Ertl* (*Fritz-Haber- Institut der Max-Planck-Gesellschaft, Berlin, Germany)
J. Phys. Chem. B, 108(48) (2004) pp. 18640–18649.
The adsorption of hydroxide on the Ag(110) surface has been studied with cyclic voltammetry, in situ second harmonic generation (SHG), and ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED). OH- is found to be adsorbed on the Ag(110) surface at potentials negative of the potential of zero charge, forming small antiphase domains of c(2 × 6) symmetry. Further adsorption leads to longer-range order and the removal of antiphase domain boundaries and is associated with a current peak in the cyclic voltammogram (CV). Concurrently, a change in symmetry patterns is observed in SHG. A c(2 × 2) pattern gradually replaces the c(2 × 6) pattern as the potential, and the OH- coverage, is increased. At the beginning of the second current wave, another symmetry change takes place which is accompanied by a sharp change in the LEED pattern from a c(2 × 2) pattern to a (1 × 1) pattern with strong background, indicating a disordered adlayer. However, RHEED results show that some patches of c(2 × 2) structure remain on the surface. The correlation between SHG and diffraction measurements and comparison of the information obtained from each technique allow to develop a detailed picture of the structures and electronic effects at the Ag(110) alkaline electrolyte interface.
A COMPARATIVE STUDY OF HYDROXIDE ADSORPTION ON THE (111), (110) AND (100) FACES OF SILVER WITH CYCLIC VOLTAMMETRY, EX SITU ELECTRON DIFFRACTION AND IN SITU SECOND HARMONIC GENERATION
S.L. Horswell*, A.L.N. Pinheiro*, E.R. Savinova, M. Danckwerts*, B. Pettinger*, M.-S. Zei*, G. Ertl* (*Fritz-Haber-Institut der Max-Planck- Gesellschaft, Berlin, Germany)
Langmuir, 20(25) (2004) pp. 10970–10981.
Hydroxide adsorption on the (111), (110), and (100) faces of silver electrodes from mixed NaOH/NaF solution is studied using cyclic voltammetry and in situ second harmonic generation (SHG). Cyclic voltammograms for the three low index silver planes in alkaline electrolytes are for the first time compared. They show two pairs of anodic and cathodic peaks in the potential interval below the equilibrium Ag/Ag2O potential. These are attributed to the specific adsorption of hydroxide ions followed by submonolayer oxide formation. The differences in the cyclic voltammograms for the (111), (110), and (100) planes are attributed to different (i) work functions, (ii) surface atomic densities, and (iii) corrugation potentials for these surfaces. Ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) show that disordered adlayers are formed on Ag(111) and Ag(100), in contrast to Ag(110), where ordered structures are produced in the region of the first pair of current peaks. In the region of the second pair of peaks, LEED indicates disordered oxide phases on each crystal plane and RHEED shows the presence of small islands of c(2 × 2) structure at some potentials on (110) and (100). SHG measurements were performed (i) in the potential scan mode at constant rotational angle and (ii) at constant potential as a function of the rotational angle. The isotropic (for the (111), (110), and (100) planes) and anisotropic (for the (110) and (111) planes) contributions to the SHG intensity were calculated by fitting the experimental data and are discussed in terms of their dependence on the charge density at the interface, on hydroxide adsorption, and on submonolayer oxide formation.
METHANE OXIDATION ON THE SURFACE OF MIXED-CONDUCTING La0.3Sr0.7Co0.8Ga0.2O3-δ
V.V. Kharton*,**, V.A. Sobyanin, V.D. Belyaev, G.L. Semin, S.A. Veniaminov, E.V. Tsipis*, A.A. Yaremchenko*, A.A. Valented***, I.P. Marozaub***, J.R. Frade*, J. Rochad*** (*Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro, Portugal; **Institute of Physicochemical Problems, Belarus State University, Minsk, Belarus; ***Department of Chemistry, University of Aveiro, Aveiro, Portugal)
Catal. Commun., 5(6) (2004) pp. 311-316.
Mixed-conductingLa0.3Sr0.7Co0.8Ga0.2O3-δ (LSCG) possesses substantial oxygen permeability, but exhibits a high activity to complete CH4 oxidation, thus making it necessary to incorporate reforming catalysts in the membrane reactors for methane conversion. Dominant CO2 formation is observed for the steady-state conversion of CH4 by atmospheric oxygen (methane/air ratio of 30:70) in a fixed bed reactor with LSCG as catalyst, and for the oxidation of CH4 pulses supplied in helium flow over LSCG powder. The conversion of dry CH4 by oxygen permeating through dense LSCG ceramics, stable operation of which under the air/CH4 gradient is possible due to the surface-limited oxygen transport, yields CO2 concentrations higher than 90%. The prevailing mechanism of total methane combustion is probably associated with weak Co–O bonding in the perovskite-related LSCG lattice, in correlation with data on oxygen desorption, phase stability and ionic transport.
ALKYLATING AGENTS STRONGER THAN ALKYL TRIFLATES
T. Kato*, E.S. Stoyanov, H. Grützmacher**, Ch.A. Reed* (*Department of Chemistry, University of California, Riverside, California; **Department of Chemistry and Applied Biosciences, Zürich, Switzerland)
J. Amer. Chem. Soc., 126(39) (2004) pp. 12451-12457.
A new class of potent electrophilic "R+" alkylating agents has been developed using weakly nucleophilic carborane anions as leaving groups. These reagents, R(CHB11Me5X6) (R = Me, Et, and i-Pr; X = Cl, Br), are prepared via metathesis reactions with conventional alkylating agents such as alkyl triflates, using the high oxophilicity of silylium ion-like species, Et3Si(carborane), as the driving force to obtain increased alkyl electrophilicity. The crystal structure of the isopropyl reagent, i-Pr(CHBB11Me5Br6), has been determined, revealing covalence in the alkylcarborane bonding. This contrasts with the free i-Pr carbocation observed when the anion is less coordinating (e.g. Sb 2F11 -) or with tertiary alkyl centers, as in [tert-butyl][carborane] salts. In solution, the reagents exist as equilibrating isomers with the alkyl group at the 7-11 or 12 halide positions of the CB11 icosahedral carborane anion. These alkylating agents are so electrophilic that they (a) react with alkanes at or below room temperature via hydride extraction to produce carbenium ions, (b) alkylate benzene without a Friedel-Crafts catalyst to give arenium ions, and (c) alkylate electron-deficient phosphorus compounds that are otherwise inert to conventional alkylating agents such as methyl triflate.
RECENT DATA ON THE NUMBER OF ACTIVE CENTERS AND PROPAGATION RATE CONSTANTS IN OLEFIN POLYMERIZATION WITH SUPPORTED Zn CATALYSTS
V.A. Zakharov, G.D. Bukatov, A.A. Barabanov
Macromol. Symp., 213(1) (2004) pp. 19-28.
Data on the number of active centers (Cp) and propagation rate constants (Kp) have been obtained by means of polymerization quenching with 14CO of propylene and ethylene polymerization with supported titanium-magnesium catalysts (TMC) with different composition. In the case of propylene polymerization the Cp and Kp values have been measured separately for isospecific, aspecific and low stereospecific centers. Effects of MgCl2 support, internal and external donors are discussed on the basis of data obtained. Data on the strong effect of diffusion limitation at ethylene polymerization with number of TMC have been obtained and a set of methods have been used to exclude this effect. Data on Cp and Kp values at ethylene polymerization with low stereospecific and highly stereospecific catalysts are presented.
SILICA-SUPPORTED ZIRCONOCENE/ (PERFLUOROPHENYL)BORATE CATALYST FOR PROPYLENE POLYMERIZATION: DRIFTS STUDY OF THE CATALYST FORMATION AND SURFACE SPECIES
V.N. Panchenko, I.G. Danilova, V.A. Zakharov, E.A. Paukshtis
J. Mol. Catal. A: Chem., 225(2) (2005) pp. 271-277.
IR spectroscopy has been used to study the interaction of silica with PhNEt2 (N) and B(C6F5)3 (B) and subsequent interaction of the support SiO2/[N+B] with dimethylzirconocene Me2Si(2-Me-Ind)2ZrMe2 (“Zr”). The data were obtained on the composition of the surface compounds appeared at both stages of catalyst synthesis. It has been shown that (B) and (N) interact with OH groups of silica to form ionic pair [H-NR3]+[(C6F5)3B-O-Si≡]− (IP-1). Cation fragment of this pair contains highly reactive N-H bond with a.b. at 3230 cm−1. It has been found that N-H groups in a part of IP-1 complexes react with neighboring OH groups of silica by hydrogen bonding that gives complexes IP-2. It has been shown that “Zr” complexes interact both with complexes IP-1 and IP-2. As “Zr” reacts with IP-1, zirconium ionic complexes IP-3 containing Zr-Me bond are formed on silica. These complexes are suggested to be the precursor of the polymerization active sites. The reaction of “Zr” with IP-2, most likely, produces surface zirconium compound containing no Zr-Me bonds and inactive for propylene polymerization.
AN IR-SPECTROSCOPIC STUDY OF THE STATE OF ZIRCONIUM IN SUPPORTED ZIRCONOCENE CATALYSTS
V.N. Panchenko, I.G. Danilova, V.A. Zakharov, E.A. Paukshtis
Kinet. Catal., 45(4) (2004) pp. 547-553.
The surface compounds of zirconium in SiO2/MAO/Cp2ZrMe2 (I) and SiO2/Cp2ZrMe2 (II) catalysts were studied by the IR spectroscopy of adsorbed CO at 93–293 K. It was found that the bridging and terminal complexes of CO were formed on the surface of the catalysts at 93 K; the adsorption of CO was reversible. At 293 K, CO was irreversibly inserted into the Zr–Me bond with the formation of various acyl compounds of zirconium; these compounds were characterized by absorption bands in the region 1495–1750 cm -1 in the IR spectrum. These data suggested the heterogeneity of the surface composition of zirconocene catalysts I and II. Catalyst I, which was active in ethylene polymerization, contained surface zirconium complexes that can be considered as the precursors of active centers for ethylene polymerization.
FERROUS RATHER THAN FERRIC SPECIES ARE THE ACTIVE SITES IN BIS(IMINO)PYRIDINE IRON ETHYLENE POLYMERIZATION CATALYSTS
K.P. Bryliakov, N.V. Semikolenova, V.N. Zudin, V.A. Zakharov, E.P. Talsi Catal. Commun., 5(1) (2004) pp. 45-48.1H NMR and EPR spectroscopic studies show that the iron centers in bis(imino)pyridine iron(II) and bis(imino)pyridine iron(III) olefin polymerization precatalysts LFeCl2 and LFeCl3 (L=bis(imino)pyridine) are converted upon treatment with methylaluminoxane (MAO) into ferrous complexes of the type [L(Me)Fe(II)(μ-Me)2AlMe2] or [LFe(II)(μ-Me)2AlMe2]+[Me-MAO]−.
THE ACTIVE INTERMEDIATES OF ETHYLENE POLYMERIZATION OVER 2,6-BIS(IMINO)PYRIDYL IRON COMPLEX ACTIVATED WITH ALUMINUM TRIALKYLS AND METHYLALUMINOXANE
K.P. Bryliakov, N.V. Semikolenova, V.A. Zakharov, E.P. Talsi
Organometallics, 23(22) (2004) pp. 5375-5378.
The intermediates of olefin polymerization over homogeneous catalysts based on bis(imino)pyridine iron(II) chloride (LFeCl2, L=2,6-bis[(1-2,6- dimethylphenylimino)ethyl]pyridine) with different activators (trimethyl-, triisobutyl-, trioctylaluminum and MAO) have been studied by 1H and 2H NMR. In conditions approaching real polymerization, neutral species of the type [LFe(II)Cl(μ-R)2AlR2] or [LFe(II)R(μ-R)2AlR2] dominate in the reaction solution in LFeCl2+AlR3 systems, whereas in LFeCl2/MAO systems, ion pairs [LFe(II)(μ-Me)(μ-Cl)AlMe2]+[Me-MAO]- (at Al/Fe < 200) and [LFe(II)(μ-Me)2AlMe2]+[Me-MAO]- (at Al/Fe > 500) are the predominant species.
MODIFICATION OF POLYETHYLENE BY SELECTIVE OXIDATION OF END DOUBLE BONDS TO CARBONYL GROUPS
S.V. Semikolenov, K.A. Dubkov, L.G. Echevskaya, M.A. Matsko, E.B. Burgina, D.E. Babushkin, V.A. Zakharov, G.I. Panov
Polymer Sci. Ser. B, 46(9-10) (2004) pp. 308-311.
It was demonstrated that the treatment of polyethylene by nitrous oxide (N2O) at 230–250°C leads to selective oxidation of end double bonds of the polymer and their quantitative conversion into carbonyl groups. Oxidation has an insignificant effect on the molecular mass distribution of the polymer and may be regarded as a new method of PE modification.
COPOLYMERIZATION OF TRIFLUOROCHLOROETHYLENE AND ALKYL VINYL ETHERS
S.S. Ivanchev, V.V. Konovalenko*, B.V. Polozov** (*AO Plastpolymer, St. Petersburg, Russia; **JSC Pigment, St. Petersburg, Russia)
Polymer Sci. Ser. B, 46(9-10) (2004) pp. 255-258.
The copolymerization of trifluorochloroethylene and alkyl vinyl ethers, a process that is widely used for manufacturing of protective coatings, was investigated. In order to raise efficiency in the use of trifluorochloroethylene–alkyl vinyl ether– hydroxyalkyl vinyl ether ternary copolymers, the possibility of eliminating copolymer structuring during polymerization through the addition of small amounts of primary alcohols or hydroxyamines was suggested and experimentally verified. Some properties of coatings based on these copolymers that were cured by toluylene diisocyanate additives were studied.
NEW BIS(ARYLIMINO)PYRIDYL COMPLEXES AS COMPONENTS OF CATALYSTS FOR ETHYLENE POLYMERIZATION
S.S. Ivanchev, G.A. Tolstikov*, V.K. Badaev, I.I. Oleinik*, N.I. Ivancheva, D.G. Rogozin, I.V. Oleinik*, S.V. Myakin (*Vorozhtsov Institute of Organic Chemistry, Novosibirsk, Russia)
Kinet. Catal., 45(2) (2004) pp. 176-182.
A new series of 2,6-bis(arylimino)pyridineiron(II) complexes with cycloaliphatic (cyclopentyl, cyclohexyl, cyclooctyl, and cyclododecyl) substituents in the ortho position of the aryl ring are synthesized and studied as components for ethylene polymerization catalysts. Methylaluminoxane is used as an activator for the complexes. The resulting catalytic systems are more active in polymerization at elevated temperatures (60-80°C) than previously described systems based on substituted 2,6-bis(arylimino)pyridines. The influence of the number of CH2 groups in a cycloaliphatic substituent on the efficiency of the catalytic system is studied. Polymers formed are characterized by an increased molecular weight, high density, and high crystallinity.
ANIMATE ETHYLENE POLYMERIZATION OVER CATALYTIC SYSTEM BIS[N-(3-TRETBUTYLSALICILIDEN) ANILINEATO]TITANDI CHLORIDE – METHYLALUMOXANE
S.S. Ivanchev, V.K. Badaev, N.I. Ivancheva, S.Ya. Khaikin
Doklady Chem., 394(5) (2004) pp. 639-642.
Kinetics of the polymerization of ethylene over a catalytic system bis[N-(3-tert-butylsalicylidene) anilinato]titanedichloride – methylalumoxane was studied. The shapes of the polymerization rate curves indicated the stable operation of the catalytic systems for long enough time (more than 30 min) at the temperature as high as 50°C. The obtained time dependencies of the molecular mass of synthesized polyethylene allowed the mechanism of animated polymerization to be established. This mechanism also was supported by calculations. Another evidence was that the addition of hexane to the ethylene feed resulted in the formation of ethylene-hexene blockcopolymer. The animated polymerization of ethylene was observed for the first time with this comparatively simple and available catalytic system.
DESIGN OF ARYLIMINE POSTMETALLOCENE CATALYTIC SYSTEMS FOR OLEFIN POLYMERIZATION. I. SYNTHESIS OF SUBSTITUTED 2-CYCLOALKYL- AND 2,6-DICYCLOALKYLANILINES
I.I. Oleinik*, I.V. Oleinik*, I.B. Abrakhmanov**, S.S. Ivanchev, G.A. Tolstikov* (*Vorozhtsov Novosibirsk Institute of Organic Chemistry, Novosibirsk, Russia; **Institute of Organic Chemistry, Ufa, Bashkortostan, Russia)
J. General Chem., 74(9) (2004) pp. 1423-1427.
An easy approach to synthesis of substituted 2-cycloalkyl- and 2,6-dicycloalkylanilines, included catalytic hydrogenation in methanol over nickel- Reney of available о-cycloalkenylanilines, produced by interaction of cyclic allyhalogenides with anilines, has been designed.
DESIGN OF SCHIFF BASE-LIKE POSTMETALLOCENE CATALYTIC SYSTEMS FOR POLYMERIZATION OF OLEFINS. II. SYNTHESIS OF 2,6-BIS(ARYLIMINOALKYL)PYRIDINES WITH CYCLOALKYL SUBSTITUENTS
I.I. Oleinik*, I.V. Oleinik*, I.B. Abrakhmanov**, S.S. Ivanchev, G.A. Tolstikov* (*Vorozhtsov Novosibirsk Institute of Organic Chemistry, Novosibirsk, Russia; **Institute of Organic Chemistry, Ufa, Bashkortostan, Russia)
J. General Chem., 74(10) (2004) pp. 1575-1579.
Reactions of substituted cycloalkylanilines with 2,6-diacetylpyridine in methanol in the presence of formic acid afforded a wide series of the corresponding bis(cycloalkylaryliminoalkyl)pyridines which can be used as ligands for the preparation of iron and cobalt complexes.
SPECTROSCOPIC INVESTIGATION OF PRODUCTS OF ULTRADISPERSED POLYTETRAFLUOROETHYLENE SUBLIMATION
L.N. Ignatieva*, A.K. Tsvetnikov*, O.N. Gorbenko*, T.A. Kaidalova*, V.M. Buznik (*Institute of Chemistry, Vladivostok, Russia)
J. Struct. Chem., 45(5) (2004) pp. 830-836.
IR-spectroscopy was used to study structure of the fractions, evolved in the process of thermal sublimation of UPTFE powder. Fractions consisted of highly amorphous fragments formed by branched chains with end olefin groups condensed at temperatures 50-160°С. Fractions, isolated at temperatures ≥300°С have the structure similar to PTFE and are highly crystalline. It is suggested, that amorphism of the samples is caused by irregular distribution of fragments with end olefin and side fluoromethyl groups in the structure.
PECULIARITITES OF THERMAL DESTRUCTION AND CALORIMETRY OF SUPERDISPERSED POLYTETRAFLUOROETHYLENE
V.M. Buznik, I.N. Mikhalin, P.P. Semyannikov*, T.S. Kukhlevskaya**, A.K. Tsvetnikov**, A.V. Kartashev*** (*Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia; **Institute of Chemistry, Vladivistok, Russia; ***Kirenskii Institute of Physics, Krasnoyarsk, Russia)
Chem. Sustain. Devel., 12(5) (2004) pp. 605-610.
Derivatography, mass-spectrometry and differential scanning microcalorimetry were used to study ultradispersed powder of terafluoroethylene, prepared by thermal gas-dynamic method (material FORUM®). The process of FORUM thermal decomposition and its thermal physical properties differs significantly from the industrial PTFE. Temperature range of the decomposition process increased more than 4 times: 465-595◦C for PTFE and 70-550◦C for FORUM. FORUM evolved wide spectrum of molecular fragments with atomic masses from 31 to 881 upon thermal decomposition. Phase transitions in crystal phase, typical for industrial PTFE, are missed.
MECHANOCHEMICAL METHODS TO OBTAIN COMPOSITE MATERIALS METALCERAMICS- POLYTETRAFLUOROETHYLENE
O.I. Lomovskii*, A.A. Politov*, D.V. Dudina*, M.A. Korchagin*, V.M. Buznik (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia)
Chem. Sustain. Devel., 5 (2004) pp. 619-626.
Solid phase mechanochemical methods to obtain new materials – metalfluoropolymer and metalceramic- fluoropolymer composites have been developed. Composite materials with high electroconductivity and low friction constant, stable to abrasion were prepared on the base of W-Cu, WC-Cu, Cu-TiB2 and ultradispersed polytetrafluoroethylene (UPTFE). Thermal stability of pure mechanically treated UPTFE and PTFE in the composite differs and depends on the nature of the main composite component.
KINETIC PECULIARITIES OF α-PINENE OXIDATION BY MOLECULAR OXYGEN
J.E. Ancel*, N.V. Maksimchuk, I.L. Simakova, V.A. Semikolenov (*Aventis Animal Nutrition S. A., France)
Appl. Catal., A, 272(1-2) (2004) pp. 109-114.
Kinetic peculiarities of α-pinene oxidation by molecular oxygen were studied. The process proceeds selectively at a low a-pinene conversion and the main products are verbenyl-hydroperoxide and α-pinene epoxide. The products ratio depends slightly on temperature, oxygen pressure and α-pinen conversion. The kinetic equation for the reaction rate was suggested.
KINETIC STUDY ON ISOMERIZATION OF VERBENOL TO ISOPIPERITENOL AND CITRAL
N.V. Maksimchuk, I.L. Simakova, V.A. Semikolenov
React. Kinet. Catal. Lett., 82(1) (2004) pp. 165-172.
Thermal isomerization of verbenol in the gas and liquid phases is discussed. The effect of temperature and residence time on the reaction mixture residence time τ of about 10-3 min for the gas phase conditions; at 200-350°C and τ = 10-80 min for the liquid phase process). The kinetic behavior and the reaction mechanisms are presented.
HETEROGENEOUS BIOCATALYSTS AND REACTORS FOR INNOVATIVE PROCESSES OF ENZYMATIC PROCESSING OF STARCH AND SUGAR
G.A. Kovalenko, O.V. Komova, I.L. Simakova, L.V. Perminova, A.V. Simakov, V.V. Khomov, S.V. Sukhinin* (*Lavrentyev Institute of Hydrodynamics, Novosibirsk, Russia)
Catal. Ind., 2 (2004) pp. 41-47.
The domestic innovative developments analyzed in this article concern the biocatalysis and describe alternative technological approach to heterogeneous processes of enzymatic hydrolysis of starchcontaining raw material and sugar into starch treacle of various composition, and invert syrups. Their essence is in production and use of highly-stable biocatalysts on the basis of ferments: glucoamylase and invertase immobilized on carbon-containing macrostructured ceramic supports. A rotary-inertial bioreactor designed for these heterogeneous biocatalysts allows increasing efficiency of the processes of enzymic hydrolysis of starch and sugar as compared with the conventional bioreactor with steady layer.
ROTOR-INERTIAL BIOREACTOR FOR HETEROGENEOUS BIOCATALYTIC PROCESSES. I. STARCH ENZYMATIC HYDROLYSIS
G.A. Kovalenko, S.V. Sukhinin*, A.V. Simakov, L.V. Perminova, O.V. Komova, V.V. Khomov, O.Yu. Borovtsova (*Lavrentyev Institute of Hydrodynamics, Novosibirsk, Russia)
Biotechnology, 1 (2004) pp. 83-90.
Comparative studies of enzymatic hydrolysis of dextrinized corn and wheat starch in innovative rotorinertial bioreactor (RIB) were carried out using heterogeneous biocatalyst obtained by adsorptive immobilization of glucoamilase on carbon-containing foam-like ceramics. Principle of RIB operation and structure, and also some characteristics in comparison with traditional fixed-bed bioreactor are given. Under optimal conditions (rotational speed of container not less than 80 turn/minute, rate of substrate feeding not more than 0,2 l/h) it was shown that efficiency of the process of corn dextrines hydrolysis and activity of heterogeneous biocatalyst in the RIB was 1,5-2 times and 3-3,5 times, correspondingly, higher than that in the traditional fixed-bed bioreactor.
CATALYTIC FILAMENTOUS CARBONS (CFC) AND CFC–COATED CERAMICS FOR IMMOBILIZATION OF BIOLOGICALLY ACTIVE SUBSTANCES
G.A. Kovalenko, D.G. Kuvshinov, O.V. Komova, A.V. Simakov, N.A. Rudina
In “Nanoengineered Nanofibrous Materials”, Eds. S.I. Guceri, Y. Gogotsi, V.L. Kuznetsov, Kluver Academic Book Publishers, Dordrecht, Netherlands, Vol. 169, 2004, pp. 251-256.
Adsorption properties of bulk catalytic filamentous carbon (CFC) granules and CFC-coated macrostructured ceramics (honeycomb monoliths, foams) have been studied for adsorptive immobilization of biologically active substances, including enzymes (glucoamylase, invertase) and nongrowing cells of bacteria. The effects of morphology of surface carbon layer on the adsorption efficiency of the supports and on the biocatalytic properties (activity and stability) of immobilized enzymes have been investigated.
HYDROXYAPATITE FORMATION IN HUMAN BLOOD
A.T. Titov*, P.M. Larionov**, A.S. Ivanova, V.I. Zaikovskii (*United Institute of Geology Geophysics and Mineralogy, Novosibirsk, Russia; **Novosibirsk Research Institute of the Pathology of Blood Circulation, Russia)
Proceedings of the International Congress on Applied Mineralogy, Eds. Picchio et. al, ICAM-BR, San-Paulo, 2004, pp. 207-210.
In existing models of the soft tissue mineralization the role of blood is limited to transport of calcium and phosphorus ions. In present study it is proved a tissue mineralization mechanism starting that hydroxyapatite (HAP) is produced in the blood plasma. This mechanism is based on the observation of HAP microcrystalls, which are similar to hydroxyapatite calcificates on heart valves and the bone apatite, in the dry blood rests of healthy donors. Modeling experiments were carried out under adjustable conditions (T = 37°C, pH = 7.4) with respect to the ionic composition of the main elements (Ca, P, Mg, and NaCl) in aqueous solution close to their contents in the blood plasma. The basic blood protein albumin was used as a biological component. Serum bovine albumin was used as the modeling protein. On the basis of experimental data it was concluded that the blood proteins promote the formation of hydroxyapatite microcrystalls. Albumin plays a special role in this process.
A COMPUTER ALGORITHM FOR NUCLEATION RATE SURFACE CONSTRUCTION
M.P. Anisimov, L.М. Anisimova*, P. Turner**, P.К. Hopke** (*Novosibirsk State University, Novosibirsk, Russia; **Clarkson University, Potsdam, USA)
In “Nucleation and Atmospheric Aerosols 2004”, Eds. M. Kasahara, M. Kulmala, Kyoto University Press, Japan, pp. 205-209.
A computer algorithm for nucleation rate surface design is developed. An obvious advantage of the computer semi-empirical design of nucleation rate surfaces is the ability to construct this surface over the full interval of nucleation parameters that are unavailable for any experiments. Examples of conditions that are difficult to achieve include very low temperatures, high-pressures and/or very hightemperature medium (such as stars) etc. It is assumed that the current algorithm can be further developed for the semi-empirical design of nucleation rate surfaces for one- and two-component systems.
EXPERIMENTAL PROOF OF THE TWO-CHANNEL NUCLEATION NEAR THE TRIPLE POINT
M.P. Anisimov, P.K. Hopke* (*Clarkson University, Potsdam, USA)
J. Aerosol Sci., 1 (2004) pp. 107-108.
An important result is following from the idea of semiempirical construction of the nucleation rate surfaces over diagram of phase equilibria. One can see two nucleation rate surfaces for two different phase states of the critical embryos in the vicinity of triple point. Each nucleation rate surface related with one independent channel of nucleation. Measurements of the aerosol size distribution, which have been done in the present research, show the existence of two nucleation rate surfaces, i.e. one surface for each phase state of critical embryos. In the present research the first measurements have been done of the relative location of the nucleation rate surfaces on the example of crystal and droplet nucleation.
SOME GENERAL REQUIREMENTS FOR VAPOR NUCLEATION RATE EXPERIMENTS
M.P. Anisimov, P.K. Hopke* (*Clarkson University, Potsdam, USA)
In “Nucleation and Atmospheric Aerosols 2004”, Eds. M. Kasahara, M. Kulmala, Kyoto University Press, Japan, pp. 173-177.
One of the reasons for the problems of nucleation theory development is the inconsistencies among experimental measurements as well as the assumptions used to interpret the experimental results. Some general requirements for nucleation experiments associated with any phase transformation of the first order are formulated. Measurement of the singlechannel nucleation rate plays the key role in comparison of the experimental data on nucleation rate and one-channel nucleation theory. Interpretation of multy channel nucleation in the approximation of one channel nucleation produce the unsolvable problem of theory and experiment consistency.
GENERALIZATION OF THE OSTWALD’S RULE ON THE EXAMPLE OF THE MULTI-CHANNEL VAPOR NUCLEATION
M.P. Anisimov, V.S. Akimov* (*Fare Eastern University of Communication, Khabarovsk, Russia)
In “Nucleation and Atmospheric Aerosols 2004”, Eds. M. Kasahara, M. Kulmala, Kyoto University Press, Japan, pp. 260-263.
The current generalization of the Ostwald rule for the formation of phases is proved on the basis of common results on nucleation. The present consideration uses the qualitative prove on the base of several plausible assumptions. The chemical reactions presented there should obey the main conclusions of the present consideration.
TOPOLOGIES OF THE NUCLEATION RATE SURFACES CONSTRUCTED OVER SOME DIAGRAMS OF PHASE EQUILIBRIA
M.P. Anisimov
In “Nucleation and Atmospheric Aerosols 2004”, Eds. M. Kasahara, M. Kulmala, Kyoto University Press, Japan, pp. 200-204.
Treatment of multiple nucleation rate surfaces in the one surface approximation can be mentioned as one of the reasons of the nucleation theory inconsistence and experimental results on nucleation. Unfortunately the most experimental data (possible from two or more nucleation rate surfaces) are interpreted in one-surface approximation of Classical Nucleation Theory. The experimental detection of nucleation rate from individual nucleation rate surface is available only in the resent time. The present research illustrates several examples of nucleation rate surface topologies which are designed over diagrams of phase equilibria. It can be shown the continuum of nucleation rare surfaces for binary system.
DESIRABLE CONDITIONS FOR VAPOR NUCLEATION RATE MEASUREMENTS
M.P. Anisimov, P.K. Hopke* (*Clarkson University, Potsdam, USA)
J. Aerosol Sci., 1 (2004) pp. 209-210.
Agreement between experimentally measured
vapor nucleation rates and current theoretical
predictions exists for only a limited number of
systems. One of the reasons for this problem is the
inconsistencies among experimental measurements as
well as the assumptions used to interpret the
experimental results. Usually the causes of these
disagreements cannot be identified. The current stateof-
the-art is such that experimental results using
different methods can lead to very different
interpretations for the same phenomenon. Some of the
problems in nucleation can be created by
inconsistencies in the models used to interpret the
experimental results./p>
SELECTIVE WATER SORBENTS FOR SOLID SORPTION CHILLER: EXPERIMENTAL RESULTS AND MODELLING
G. Restuccia*, A. Freni*, S. Vasta*, Yu.I. Aristov (*CNR – Istituto di Tecnologie Avanzate per l'Energia "Nicola Giordano", Messina, Italy)
Int. J. Refrig., 27(3) (2004) pp. 284-293.
In this paper the experimental results of a labscale chilling module working with the composite sorbent SWS-1L (mesoporous silica gel impregnated with CaCl2) are presented. The interesting sorption properties of this material yield a high COP = 0.6 that gives a promising alternative to the common zeolite or silica gel for application in solid sorption units driven by low temperature heat (T ≤ 100°C). The measured low specific power of the device is a result of not optimised geometry of the adsorber and of the pelletised shape of the adsorbent. Heat transfer optimisation is currently under progress to increase the specific power. The experimental results are compared with those of a mathematic model able to describe the dynamic behaviour of the system. The model is used to study the influence of the main operating parameters on the system performance.
ENVIRONMENTALLY APPROPRIATE ADSORPTIVE COOLER BASED ON THE ECOLOGICALLY SOUND “WATER–SWS-1K ADSORBENT”: LABORATORY PROTOTYPE
>G. Restuccia*, A. Freni*, S. Vasta*, M.M. Tokarev, Yu.I. Aristov (*CNR – Istituto di Tecnologie Avanzate per l'Energia "Nicola Giordano", Messina, Italy)
Chem. Sustain. Devel., 12(2) (2004) pp. 211-216.
Test results on a laboratory prototype of the adsorptive cooler based on the ecologically sound “water–SWS-1K adsorbent” working pair are discussed. The adsorbent relates to the family of selective water sorbents; this is a mesoporous silica gel KSK modified with calcium chloride. The device produces cold water (at the temperature of 5–10°C) to be used for air conditioning, food storage etc. The testing demonstrates coefficient of performance (COP) of the device as high as 0.6 at a low temperature of water desorption (90–95°C); as a result, the adsorbent may be a real alternative to the traditional materials (silica gel, zeolites) which are used for ecologically friendly adsorption systems to utilize low potential heat (T 100°C).
SOME ECOLOGICAL AND ECONOMIC ASPECTS OF APPLICATION OF SORPTIVE HEAT PLANTS IN RUSSIA
Yu.I. Aristov
Chem. Sustain. Devel., 12(6) (2004) pp. 751-755.
Ecological and economic aspects of application of sorptive heat plants (refrigerators and heat pumps) in Russia, as well as competitiveness of these devices against the traditional systems are considered. The utilization of heat wastes (or solar energy) is shown to make the sorptive refrigerators more ecologically sound and economically profitable than the compressive ones. When regenerated through combustion of natural gas, the sorptive plants can only provide no ecological damage as an exceptional case; therefore, it seems reasonable to advance the compressive devices with high coefficients of performance (СОР ≥ 4) to minimize wastes of greenhouse gases. The sorptive heat pumps with coefficients of augmentation COA > 1 are more ecologically sound and economically profitable than gas heaters. The natural gas consumption is decreased by 41 and 33% at СОАabs = 1.7 and 1.5, respectively. These results are of considerable practical interest.
SELECTIVE WATER SORBENTS FOR AIR DEHYDRATION: FROM TEST-TUBE TO INDUSTRIAL ADSORBER
Yu.I. Aristov
Catal. Ind., 6 (2004) pp. 36-41.
Properties of industrial desiccant IK-011-1 based on aluminum oxide modified by calcium chloride are described. The desiccant was developed in Boreskov Institute of Catalysis for removal of water out of process air and other gases. This material is characterized by high dynamic sorptive capacity, low dew point of desiccated gas and good hydrothermal stability. In a short time it will pass from laboratory studies of structure and properties to its pilot tests, organization of its production and supply to customers.
KINETICS OF CARBON DIOXIDE SORPTION BY THE COMPOSITE MATERIAL K2CO3 IN Al2O3
V.E. Sharonov, A.G. Okunev, Yu.I. Aristov
React. Kinet. Catal. Lett., 82(2) (2004) pp. 363-369.
The kinetics of the CO2 sorption by a composite sorbent K2CO3 in Al2O3 was studied in a gradientless adsorber at 295 K. The order of the sorption rate with respect to the CO2 concentration was found to be n = 1.04 ± 0.07. The sorption rate constants were evaluated for sorbent grains of various sizes between 0.25 and 2.1 mm. It was shown that the rate constant is proportional to the grain reciprocal radius. The dynamic capacity was obtained as a function of the CO2 concentration. The maximum sorption capacity was found to be 83 mg of CO2 per 1 g of the sorbent.
DEVELOPMENT OF MONOLITHIC CATALYSTS WITH LOW NOBLE METAL CONTENT FOR DIESEL VEHICLE EMISSION CONTROL
S.A. Yashnik, V.V. Kuznetsov, Z.R. Ismagilov, V.V. Ushakov, N.M. Danchenko*, S.P. Denisov* (*Ural Electrochemical Plant, Novouralsk, Russia)
Top. Catal., 30(31) (2004) pp. 293-298.
Monolith washcoated catalysts with potential for diesel emission control have been developed. Two types of catalysts have been prepared for further study: (1) MnOx supported on granulated γ-Al2O3, (2) MnOx supported on cordierite monolith washcoated with γ-Al2O3. Both catalysts have been calcined at 500 and 900°C and subsequently modified by doping with 0.1– 1.0 wt% of Pt or Pd. The influence of the concentration of both manganese oxide (0–10 wt%) and noble metals Pt and Pd in the range 0–1.0 wt% on the catalytic activity in methane oxidation has been studied. Comparison of the catalytic activity of MnOx/Al2O3 and MnOx + Pt(Pd)/Al2O3 with that of a standard 1 wt% Pt/Al2O3 catalyst shows the existence of a synergetic effect. This effect is more pronounced for the samples calcined at 900°C. The developed monolithic catalysts MnOx + Pt(Pd)/Al2O3 demonstrate higher activity and thermal stability (up to 900°C) compared to the commercial monolithic catalyst (TWC's).
OXIDATION DESTRUCTION OF CHLORINATED ORGANICS ON FIBER GLASS CATALYSTS
B.S. Bal’zhinimaev, E.A. Paukshtis, L.G. Simonova, L.V. Malysheva, A.N. Zagoruiko, V.N. Parmon
Catal. Ind., 5 (2004) pp. 21-27.
Glass fiber based Pt-containing catalysts for oxidizing destruction of chlorinated organics including vent gases from vinyl chloride production were developed. The catalyst modification with Al (to increase acidity) as well as doping with Mn, Cu and Co, in particularly, provide the complete and highly selective oxidation of different chlorine hydrocarbons into HCl, CO2 and H2O under the reaction conditions mild enough without formation of highly hazardous by-products, for example, molecular chlorine, phosgene and chlorinated dioxins. An addition of propane and water substantially improves the destructive efficiency of polychlorided compounds. Long term testing (more than 100 h) at temperatures lower than 550°C showed high stability of glass fiber catalysts.
OXIDATIVE NEUTRALIZATION OF ALKALINE SULFIDE DRAINS
N.М. Dobrynkin, М.V. Batygina, B.S. Bal’zhinimaev, О.L. Elin*, Ch.Ch. Rakhimov*, А.S. Noskov (*JSC “Salavatnefteorgsintez”, Salavat, Russia)
Catal. Ind., Special issue (2004) pp. 32-40.
The process of liquid-phase oxidation of sulfidecontaining waste water by oxygen over porous Sibunit graphitic material used as a catalyst and an adsorbent has been investigated. The process of purification comprises two successive stages. Initially toxic sulfides are neutralized by catalytic oxidation into sulfates. Then organic substances, being in the water phase and capable to be isolated out of waste waters at increased temperatures, are successively adsorbed from the solution and oxidized in catalytic manner into carbon dioxide and water. The experiments were carried out in the full-mixed static installation with a high-pressure reactor and in the continuous flow installation. Conversion and selectivity of sulfides-tosulfates oxidation were determined under different modes of operation. It is shown that sulfite-ions and thiosulfate-ions are formed upon sulfide-ions oxidation at temperature < 80°C and sulfates are formed in temperature range of T = 100¸ 130°C. It was found that Sibunit possesses the highest catalytic activity in sodium sulfide to sulfate oxidation, activity of metal sulfides and cobalt phthalocyanine supported on Sibunit being lower than the initial Sibunit. As for supported catalysts, selectivity of oxidation to sodium sulfate increases upon the decreasing of the content of active component, approaching the characteristics for pure Sibunit. Use of Sibunit as a catalyst in oxidation reactions as well as an adsorbent for extraction of organic substances from waste waters allows oxidation of sulfide-ions to sulfates at T = 110¸ 130°C and oxidation of sulfur-organic and organic components at T = 200¸ 240°C and solves a problem of neutralization of toxic substances containing in alkaline sulfide waste waters.
AROMATIZATION OF LIGHT NAPHTHA FRACTIONS ON ZEOLITES. II. MODEL OF CATALYST DEACTIVATION
N.M. Ostrovskii, S.A. Rovenskaja*, G.V. Echevsky (*Omsk State University, Omsk, Russia)
Hemijska Industrija, 58(3) (2004) pp. 104-108.
A model of catalyst deactivation in the “Zeoforming” process was developed. The deactivation rate constant and activation energies were estimated. The role of adsorbed oligomers in the reaction and deactivation kinetics were examined. The model is intended for further modeling and optimization of the process.
DIRECT INSERTION OF METHANE INTO C3–C4 PARAFFINS OVER ZEOLITE CATALYSTS: A START TO THE DEVELOPMENT OF NEW ONE-STEP CATALYTIC PROCESSES FOR THE GAS-TO-LIQUID TRANSFORMATION
G.V. Echevsky, E.G. Kodenev, O.V. Kikhtyanin, V.N. Parmon
Appl. Catal. A, 258(2) (2004) pp. 159-171.
The paper demonstrates that utilization of the well-known concept of the ability of the same catalytic centers to catalyze both forward and backward reactions can result in the development of a process of the direct one-step insertion of methane into heavier hydrocarbons. The insertion seems to proceed as a part of linear alkanes dehydrocyclization reactions at rather mild pressure and temperature conditions (at 773–823 K) over Zn- or Ga-promoted zeolite catalysts. The experimental study of the process evidences in its potential practical applicability for the natural gas-to-liquid conversion.
THIOPHENE CONVERSION IN THE BIMF PROCESS
D.G. Aksenov, O.V. Klimov, G.V. Echevsky, E.A. Paukshtis, A.A. Budneva
React. Kinet. Catal. Lett., 83(1) (2004) pp. 187-194.
Catalytic conversion of an oil distillate with the added extra amounts of thiophene over a zeolite catalyst was studied. The rate of the catalyst deactivation was found to increase with the increase in the thiophene concentration in the feed. A possible pathway of the thiophene conversion is discussed.
BIPHENYL OXIDATION WITH NITROUS OXIDE ON MFI ZEOLITES
D.P. Ivanov, L.V. Piryutko, V.I. Sobolev
Petroleum Chem., 44(5) (2004) pp. 322-327.
The gas–phase reaction of biphenyl oxidation with nitrous oxide on iron-containing zeolite MFI was studied. It was shown that the main products of this reaction were monosubstituted phenylphenols, which were represented predominantly by para- and meta-isomers. Optimal reaction conditions, ensuring a high selectivity for phenylphenols (~95%), were found. The initial catalyst productivity was ~1.5 mmol of PhPhOH/(g h). The activity decreased in the course of the reaction as a result of catalyst deactivation by coking.
HYDROGENATED Zr-Fe ALLOYS CAPSULATED IN Al2O3/Al MATRIX AS CATALYSTS FOR FISCHER-TROPSCH SYNTHESIS
S.F. Tikhov, V.I. Kurkin*, V.A. Sadykov, E.V. Slivinsky*, Yu.N. Dyatlova, A.E. Kuzmin*, E.I. Bogolepova*, S.V. Tsybulya, A.V. Kalinkin, V.B. Fenelonov, V.P. Mordovin* (*Topchiev Institute of Petrochemical Synthesis, Moscow, Russia)
Stud. Surf. Sci. Catal., 147 (2004) pp. 337-342.
The genesis of the ZrFe intermetallides with different atomic ratios during preparation of ZryFezHy/Al2O3/Al catalysts and their performance in Fischer-Tropsch synthesis have been studied. The effect of structural, surface and textural properties on their activity has been discussed.
HYDROGENATION OF DIALKYL DISULFIDES ON SUPPORTED SULFIDE CATALYSTS
A.V. Mashkina, L.N. Khairulina
Petroleum Chem., 44(1) (2004) pp. 52-57.
The reduction of dimethyl and diethyl disulfides by hydrogen under atmospheric pressure in the presence of sulfide catalysts with different compositions was studied. Methanethiol or ethanethiol, respectively, was the main reaction product on all catalysts at T = 200°C. The same behavior was observed for the hydrogenation of dimethyl and diethyl disulfides, but the rate of transformation of diethyl disulfide on most catalysts was higher than that of dimethyl disulfide. In the formation of alkanethiols, alumina-supported metal sulfides were more active than those supported on carbon or silica gel. Among the alumina-based catalysts, tungsten sulfide was least active and rhodium sulfide was most active. In the presence of the aluminorhodium sulfide catalyst, the reaction rate increased with temperature and with an increase in the initial concentrations of hydrogen and dimethyl disulfide in the reaction mixture to 15 vol % and 2 vol %, respectively
.MODELING OF THE OXIDATION OF ORGANIC COMPOUNDS IN SUPERCRITICAL WATER
A. Yermakova, V.I. Anikeev
Theor. Found. Chem. Engin., 38(4) (2004) pp. 333-340.
A system for oxidation of organic impurities in supercritical water is proposed. Models are formulated and calculations are performed to determine the characteristics of the main apparatuses of the system, namely, heat exchangers, a chemical reactor, and a separator. The models take into account specific features of processes under supercritical conditions, specifically, the changes in the thermodynamic properties (enthalpy, specific heat, critical parameters) of the reaction mixtures with changes in pressure and temperature, and also the variations of the compositions of the mixtures along the lengths of the apparatuses. The thermodynamic properties are calculated by methods of nonequilibrium thermodynamics. A numerical analysis is performed of one of the variants of a system for acetic acid oxidation by oxygen in supercritical water, which can be a prototype of a pilot plant. The fuel is chosen to be an aqueous methanol solution, and the oxidant is taken to be hydrogen peroxide. Replacement of the reactant, the fuel, or the oxidant does not fundamentally change the methods for calculating the characteristics of the apparatuses and the entire system.
EFFECT OF PRESSURE ON THE RATE CONSTANT OF THE DECOMPOSITION OF ALIPHATIC NITROCOMPOUNDS IN SUPERCRITICAL WATER
V.I. Anikeev, A. Yermakova, A.V. Golovizin, M. Hoto* (*Kumamoto University, Kumamoto, Japan)Russ. J. Phys. Chem., 78(10) (2004) pp. 1553-1559
It was found that the observed first-order rate constant for the decomposition of aliphatic nitrocompounds RNO2 in supercritical water at constant temperature increases exponentially with the pressure. The volumes of activation for the reactions under study were determined. The experimental data were described within the framework of the transitionstate theory. Conclusions on the nature of the activated complex have been drawn. The calculated values of the volume of activation for the decomposition of nitromethane, nitroethane, and 1-nitropropane in supercritical water are similar, a result indicative of the same nature of the activated complex in all three cases. The true rate constant for the decomposition of these nitrocompounds in supercritical water decreases virtually linearly in the series NM > NE > NP.
THE USE OF CUBIC EQUATIONS OF STATE FOR CALCULATING THE THERMODYNAMIC AND THERMOPHYSICAL PROPERTIES OF MULTICOMPONENT NONIDEAL MIXTURES
A. Yermakova, A.V. Golovizin, V.I. Anikeev
Russ. J. Phys. Chem., 78(11) (2004) pp. 1723-1728.
Calculations of the enthalpy and heat capacity of a multicomponent mixture in the critical region of its parameters with the use of cubic equations of state are considered. The possibility of describing the anomalous behavior of these mixture properties in the supercritical region is demonstrated. Examples that illustrate the behavior of the partial molar properties of components and averaged mixture properties such as heat capacity and enthalpy close to the critical point of the mixture are given. The influence of nonideality characteristic of mixtures in the near-critical state on the heat effects of chemical transformations and adiabatic mixture heating values was determined.
KINETICS AND THERMODYNAMICS OF 2-PROPANOL DEHYDRATION IN SUPERCRITICAL WATER
V.I. Anikeev, A. Yermakova, J. Manion*, R. Huie* (*National Institute of Standards and Technology, Gaithersburg, MD, USA)
J. Supercrit. Fluids, 32(1-3) (2004) pp. 123-135.
Kinetics and thermodynamics of 2-propanol dehydration in supercritical water (SCW) and the effect of density on this reaction have been investigated in a batch reactor. The studies were performed at water densities between 0.24 and 0.58 g/cm3 and temperatures between 654 and 686 K. The main reaction products of 2-propanol dehydration were propene and water. Rate of the reaction was found to depend essentially on the water density. Two models are used to predict the effect of SCW density on the rate constant of 2-propanol dehydration reaction: a thermodynamic model (the model of activated complex) and a model of acid-catalyzed reaction. Redlich–Kwong–Soave equation of state was used for calculation of the partial molar volumes of the reaction participants in SCW including a transition state and activation volume of the reaction. Application of the activated complex model demonstrated that the calculated values of the activation volume depend strongly on pressure at fixed temperature, which contradicts the experimental data where the activation volume is independent of pressure. At the same time, the mechanism of 2-propanol dehydration reaction in SCW was shown to correlate well with the acid-catalyzed mechanism in solutions. Rate of the reaction is directly proportional to the concentration of 2-propanol and H3O+ ions. An increase in the Hsub>3O+ concentration in SCW with density correlates unequivocally with an increase in the reaction rate.
KINETIC MODEL OF THE REACTION OF METHANOL WITH HYDROGEN SULFIDE
A. Yermakova, A.V. Mashkina
Kinet. Catal., 45(4) (2004) pp. 522-529.
p>The kinetics of the reaction of methanol with hydrogen sulfide in the presence of an IKT-31 catalyst was experimentally studied. The experiments were performed in a fixed-bed flow reactor under the following conditions: T = 598–653 K, P = 0.1–1.0 MPa, and / = 0.4–15.0. Rate equations were derived which describe the rates of formation of methanethiol as the main product and dimethyl sulfide and dimethyl ether as by-products. The rate constants and activation energies were found by the mathematical Treatment of experimental data. The model proposed can be used for reactor design.KINETICS OF INTERACTION OF TOLUENE WITH A PRE-OXIDIZED VANADIA/TITANIA CATALYST
E.A. Ivanov, S.I. Reshetnikov, D.A. Bulushev* (*Swiss Federal Institute of Technology, Lausanne, Switzerland)
React. Kinet. Catal. Lett., 82(1) (2004) pp. 199-206.
A kinetic model for the interaction of toluene with a pre-oxidized vanadia/titania catalyst has been developed. The model is based on two types of oxygen sites and includes 5 steps. It describes satisfactorily the transient behavior of toluene and products (benzaldehyde, CO2) in the temperature range of 523-633 K.
STUDY OF BENZENE SORPTION IN H-ZSM-5 ZEOLITE UNDER CATALYTIC CONDITIONS
S.I. Reshetnikov, S.B. Ilyin, A.A. Ivanov, A.S. Kharitonov
React. Kinet. Catal. Lett., 83(1) (2004) pp. 157-164.
The equilibrium of the sorption of benzene in an H-ZSM-5 zeolite has been investigated in the temperature range of 100-400°C and at partial pressures 0.11÷0.57 atm. The data on the sorption under these conditions could be fitted with the Langmuir isotherms taking into account a linear decrease in heats of sorption with the increase in the sorbate loading. The equilibrium constants and heat of the sorption have been determined.
NEW LARGE-CAPACITY PROCESS OF PRODUCING NITROUS OXIDE
A.S. Noskov, I.A. Zolotarskii, S.A. Pokrovskaya, E.M. Slavinskaya, V.V. Mokrinsky, V.N. Kashkin, V.N. Korotkikh, I.A. Polukhina
Catal. Ind., 1 (2004) pp. 5-11.
The article is devoted to development of largecapacity process to produce nitrous oxide by selective oxidation of ammonia with oxygen over oxide catalysts MnO2-Bi2O3/α-Al2O3 developed in the Boreskov Institute of Catalysis. The kinetic studies carried out at T = 270÷400°C and P = 0,1÷ 0,6 MPa have shown that oxidation of ammonia over the mentioned catalysts proceeds in two main parallel routes with formation of N2O and N2. Selectivity to nitrous oxide was 88–90 % in the temperature range of T = 340÷360°C and selectivity to NO does not exceed 1 % within the whole range of the experimental conditions. The kinetic data obtained were used for mathematical modeling of the process to produce nitrous oxide in fluidized-bed reactors and in tubular reactors. It was shown that in spite of significant thermal effects, the reaction mixture with the ratio ammonia : oxygen = 1 : 1 may be used in fluidized bed reactor. Design nitrous oxide selectivity was 85,6 % at ammonia conversion of 98 %. The mathematical modeling of the process in a tubular reactor showed the maximum permissible ammonia concentration at the inlet of the reactor upon stable thermal operation modes are realized to increased from 4,5 to 8 vol. % when passing from spherical catalyst to grains in the form of Rashig rings. Pilot tests of the process were carried out in reactors of fixed bed and fluidized bed and their total time period was ~ 700 h. As a result, the catalyst was shown to maintain activity and selectivity both in the fluidizedbed and in a tubular reactors during all the test time. In both reactor types, selectivity to nitrous oxide was 86-88 % with ammonia conversion of 95–98 %. Based on the mathematical modeling and the pilot tests, a process flowsheet was developed. It provides production of nitrous oxide of ~ 3 ruble/kg in first cost with content of the purpose product no less than 86 % (the rest is nitrogen)
THERMAL PROCESSES STUDY IN CATALYTIC SOOT FILTERS FOR DIESEL EXHAUST TREATMENT
T.L. Pavlova, N.V. Vernikovskaya. N.A. Chumakova, A.S. Noskov
J. “Combustion, Explosion and Shock Waves”, 40(3) (2004) pp. 14-21.
For a catalytic diesel particulate filter with quartz foam structure, mathematical modeling of both the soot particles filtration and the catalytic oxidation regeneration are presented. Two different operation modes are under consideration, first of them is successive filtration and regeneration, while the second one is combining filtration at a higher temperature and simultaneous catalytic combustion of the soot particles. The influence of process parameters on the system dynamics was studied. It was shown that in the case of rather small particles it is efficient to follow the first operation mode, while for the diesel exhaust treatment with bigger soot particles one should prefer the second strategy.
UTILIZATION OF REACTION HEAT IN PROCESS OF METHANE OXIDATION FROM VENT GASES OF COAL MINES: PILOT TESTS
N.A. Chumakova, O.P. Klenov, D.A. Stepanov, V.N. Korotkikh, P.G. Tsyrulnikov, A.S. Noskov
Catal. Ind., Special issue (2004) pp. 45-53.
Some results of pilot tests of a catalytic reactor for oxidation of lean methane-air mixtures that simulate the vent gases from coal mines are presented. The main goal of the study is the experimental verification whether the catalytic reverse-process is efficient for utilization of such gases and simultaneous hightemperature heat production. The experiments have shown the efficiency of unsteady state process in a fixed-bed reactor with 0,5 wt % Pd/γ-Al2O3 catalyst and inert packing at the reactor ends. In this case, a periodical reverse of the gas flow in the reactor takes place and a part of the gas flow can be withdrawn from the central part of the high-temperature zone of the layer into an outer heat exchanger. Autothermal operation of the apparatus with methane concentration of no less than 0,4 vol. % and a possibility of utilization of more than 80 % of reaction heat at methane concentration of 0,61 vol. % was shown.
THE KINETIC MODEL OF FORMATION OF NANOFIBROUS CARBON FROM CH4–H2 MIXTURE OVER A HIGH-LOADED NICKEL CATALYST WITH CONSIDERATION FOR THE CATALYST DEACTIVATION
S.G. Zavarukhin, G.G. Kuvshinov
Appl. Catal. A, 272(1-2) (2004) pp. 219-227.
A mathematical model is suggested for the process of formation of nanofibrous carbon from the mixture of methane and hydrogen over a high-loaded nickel catalyst (90 wt.% Ni-Al2O3) to describe the observed process kinetics involving the catalyst deactivation. The experimental kinetic data obtained at hydrogen volume fraction of 0 to 40%, 490-590°C and atmospheric pressure are analyzed to suggest the formula for calculation of the maximal rate of the carbon formation and the equation of the catalyst deactivation. The suggested kinetic model relates to the mechanism when the cleavage of the first hydrogen atom from a methane molecule adsorbed on the catalyst surface is the rate limiting stage. The model is appropriate for the qualitative and quantitative description of the process under consideration. The calculations in terms of the model are exemplified with synthesis of nanofibrous carbon in an isothermal perfect-mixing reactor at a constant methane consumption. The calculated results agree well with the experimental data.
ALGORITHM BIDIMS FOR AUTOMATED SYSTEMATIZATION OF DATA ARRAY. CASE STUDY: REDISCOVERING MENDELEEV’S PERIODIC TABLE OF CHEMICAL ELEMENTS
A.N. Zagoruiko, N.G. Zagoruiko* (*Institute of Mathematics, Novosibirsk, Russia)
Int. J. "Inform. Theor. & Applic.", 11(4) (2004) pp. 309-318.
The method (algorithm BIDIMS) of multivariate objects display to bidimensional structure in which the sum of differences of objects properties and their nearest neighbors is minimal is being described. The basic regularities on the set of objects at this ordering become evident. Besides, such structures (tables) have high inductive opportunities: many latent properties of objects may be predicted on their coordinates in this table. Opportunities of a method are illustrated on an example of bidimentional ordering of chemical elements. The table received in result practically coincides with the periodic Mendeleev table.
THREE-DIMENSIONAL NUMERICAL SIMULATION OF A NONSTATIONARY GRAVITATING N-BODY SYSTEM WITH GAS
V.N. Snytnikov, V.A. Vshivkov*,**, E.A. Kuksheva, E.V. Neupokoev**,***, S.A. Nikitin****, A.V. Snytnikov**,*** (*Institute of Computational Technologies, Novosibirsk, Russia; **Novosibirsk State Technical University, Novosibirsk, Russia; ***Institute of Computational Mathematics and Mathematical Geophysics, Novosibirsk, Russia; ****Institute of Nuclear Physics, Novosibirsk, Russia)
Astronomy Lett., 30(2) (2004) pp. 134-146.
A three-dimensional numerical model to investigate nonstationary processes in gravitating N-body systems with gas has been developed. Efficient algorithms were used for solving the Vlasov and Poisson equations that included the evolutionary processes under consideration, which ensures rapid convergence at high accuracy. Examples of the numerical solution of the problem on the growth of physical instability in the model of a flat rotating disk with a gaseous component and its threedimensional dynamics under various initial conditions including a nonzero velocity dispersion along the rotation axis are given.
ION-ACOUSTIC TYPE INSTABILITY IN PROTOPLANETARY DISK
S.A. Nikitin*, V.N. Snytnikov, V.A. Vshivkov** (*Budker Institute of Nuclear Physics, Novosibirsk, Russia; **Institute of Computational Technology, Novosibirsk, Russia)
In “Plasma in the Laboratory and in the Universe”, AIP Conference Proceedings Series: N.Y., Vol. 703, 2004, pp. 280-283.
The computer simulations showed that gravitational instability development in the two-phase medium of gas-dust circumstellar disk is the mechanism of protoplanets formation. At the nonlinear stage of instability development, the soliton density waves of high gas density form.
MAGNETIC FIELDS IN PROTOPLANETARY AND GALACTIC DISKS
S.A. Nikitin*, V.N. Snytnikov, V.A. Vshivkov** (*Budker Institute of Nuclear Physics, Novosibirsk, Russia; **Institute of Computational Technology, Novosibirsk, Russia)
In “Plasma in the Laboratory and in the Universe”, AIP Conference Proceedings Series: N.Y., Vol. 703, 2004, pp. 284-287.
Time dependent 3D distributions of magnetic field generated by electrical currents in galactic/circumstellar discs of various spatial structures (the rings, spirals and matter clusters and others) have been obtained via 3D self-consistent numerical modeling using nonstationary Vlasov- Liouville's equation for particles and the Poisson's equation for self-consistent potential.
FLUIDIZED-BED REACTOR FOR DIRECT HYDROGEN SULFIDE OXIDATION TO ELEMENTAL SULFUR: EXPERIENCE OF CREATION OF EXPERIMENTAL INDUSTRIAL INSTALLATION AT BAVLINSKOE OILFIELD (TATARSTAN REPUBLIC)
Z.R. Ismagilov, S.R. Khairulin, M.A. Kerzhentsev, A.N. Golovanov*, A.A. Golovanov*, A.M. Mazgarov**, A.F. Vil'danov**, Sh.F. Takhautdinov***, F.A. Zakiev*** (*JSC “TATNIINEFTEMASH”, Kazan, Tatarstan; **State Unitary Enterprise “VNIIUS”, Kazan, Tatarstan; ***JSC “TATNEFT” Almetievsk, Tatarstan)
Catal. Ind., Special issue (2004) pp. 50-54.
The description of an experimental-industrial installation for catalytic process of direct hydrogen sulfide oxidation to elemental sulfur in fluidized bed reactor for purifying of casing-head oil-gases at Bavlinskoe Oilfield (Tatarstan Republic) is given. The structure of the fluidized-bed reactor and plant processing characteristics are given.
NEW APPROACHES TO THE FISCHERTROPSCH SYNTHESIS PROCESS. ADVANTAGES OF MEMBRANE REACTORS
A.A. Khassin
Russ. Chem. J., 47(6) (2003) pp. 36-47.
The analysis of the specific features of the Fischer-Tropsch synthesis helps formulating the most important requirements to the FTS reactor. Membrane reactor designs can be useful for the FTS process application. Semi-permeable hydrogen-selective distributors allow to control the H2:CO ratio along the catalyst bed and thus enhance the selectivity of the process. Membranes of extractor type can help to improve the FTS performance by selective removing water from the reaction volume. On the other hand, plug-through contactor membrane reactor design (PCM) seems to meet all the other requirements, ensuring the high concentration of the catalyst, isothermicity, high gas-liquid interface area, small effective diffusion length and reasonable hydraulic resistance. Varying the membrane composition and conditions of its preparation leads to the changes in porous structure parameters of the PCM membrane. This allows to weaken the diffusion constrains in a predictable way and, therefore, to control the productivity and selectivity of the Fischer-Tropsch process.
NEW DATA ON THE MECHANISM OF THE METHANE STEAM REFORMING OVER NICKEL AND RUTHENIUM CATALYSTS
I.I. Bobrova, N.N. Bobrov, V.V. Chesnokov, V.N. Parmon
Chemical Engineering Transaction, Ed. S. Pierucci, Italy, Vol. 4, 2004
The kinetics of the steam reforming and pyrolysis of methane on Ni-Al2O3 and Ru/Al2O3(T = 650- 750°C, = 0.001-0.030 MPa) via an improved flow-recycling method has been studied. The values of the rates and activation energies are compared. It is shown that the steam reforming may proceed by either a heterogeneous or heterogeneous-homogeneous mechanism depending on the process conditions. The comparative activities of nickel and ruthenium catalysts at the occurrence of the process in both heterogeneous and heterogeneous-homogeneous modes are discussed.
EXPERIMENTAL STUDY OF HEAT REGIMES ON A DRY, PARTIALLY OR COMPLETELY WETTED AND LIQUID FILLED CATALYST PARTICLE
V.A. Kirillov, A.V. Kulikov, N.A. Kuzin, A.B. Shigarov
Chem. Eng. J., 98(3) (2004) pp. 219-235.
Steady-state and dynamic-heat regimes on the dry, partially wetted, and completely filled catalyst particles were studied using the model reactions of benzene, α-methylstyrene and octene hydrogenation over the several catalysts with different porous structures, apparent catalytic activities, and heat conductivities. A rise in the particle temperature at the external limitation regime was studied and the effective diffusion coefficients of limiting species were determined. The regime of particle preheating, gas temperature, hydrogen saturation of AMS or octene vapors, and the liquid mass flow rate on the top of a catalyst particle were varied. The phase equilibrium between the vapor saturated hydrogen and the partially wetted catalyst particle is found to essentially affect for dynamic runaway of the particle. According to the measured center and surface temperatures of each particle, there are two significantly different steady states in the range of liquid flow rates. A catalyst wetted by liquid and blown off with dry hydrogen provides a temperature hysteresis phenomenon. This phenomenon is characterized by the regime when the catalyst particle is almost liquid filled and its temperature is lower than that of gas. Another hightemperature regime occurs if a catalyst particle is almost dry and its temperature is higher than that of gas. Ignition and extinction dynamics of the catalyst particle were studied under conditions of the combined evaporation and hydrogenation processes.
OPTIMIZATION OF THE ACTIVE COMPONENT DISTRIBUTION THROUGH THE CATALYST BED
V.M. Khanaev, E.S. Borisova, A.S. Noskov
Chem. Eng. Sci., 59(6) (2004) pp. 1213-1220.
A variational problem was formulated to determine the optimal axially non-uniform catalyst activity distribution along the fixed catalyst bed. It was observed that the mass transport limitations or non-isothermal temperature profile are necessary conditions for potential optimization of the catalyst distribution along the bed length. Under isothermal conditions with linear dependence of the reaction rate on concentration at a constant mass transfer coefficient, the uniform distribution is optimal. Analytical solution for the firstorder reaction and numerical solutions for power-law kinetics were found.
IMPROVEMENT OF THE CATALYTIC MONOLITHS EFFICIENCY FOR CO OXIDATION USING NON-UNIFORM ACTIVE COMPONENT DISTRIBUTION ALONG THE MONOLITH LENGTH
V.M. Khanaev, E.S. Borisova, L.I. Galkina, A.S. Noskov
Chem. Eng. J., 102(1) (2004) pp. 35-44.
It is shown that the efficiency of catalytic packages can be improved using two approaches. The monotone increase of the active component concentration towards the monolith outlet is shown optimal for minimization of the total active component loading at the preserved purification degree. To resolve the problem of achieving the maximal purification degree at a fixed quantity of the active component, it is preferable to concentrate the active component near the duct entrance.
COMPACT RADIAL REACTOR WITH A STRUCTURED METAL POROUS CATALYST FOR CONVERSION OF NATURAL GAS TO SYNTHESIS GAS: EXPERIMENT AND MODELING
V.A. Kirillov, A.S. Bobrin, N.A. Kuzin, V.A. Kuzmin, A.B. Shigarov, V.B. Skomorokhov, E.I. Smirnov, V.A. Sobyanin
Ind. Eng. Chem. Res., 43(16) (2004) pp. 4721-4731.
To perform the catalytic conversion of natural gas to synthesis gas, a compact radial reactor supplied with a structured porous metal catalyst has been designed. The reactor was tested at normal pressure using natural gas and air. The reactor can operate without preheating of the inlet gas mixture. A novel structured porous metal catalyst was developed on the basis of the 7% Ni/α-Al2O3 commercial catalyst and Ni-Cr powders. The catalyst is characterized by a low hydraulic pressure drop and a high tortuosity coefficient of the regular structure. The coefficient of heat conductivity of the structured catalyst and the coefficient of mass transfer between a gas flow and the catalyst were determined in special experiments. The catalyst temperature and outlet gas concentrations were experimentally investigated with respect to the gas-air flow rate and methane concentration in the mixture. The catalyst temperature drop along the reactor radius was no higher than 230°C. The maximum catalyst temperature does not exceed 1090°C for all runs. At volumetric flow rates of the gas mixture of 4000-40000 h-1 and O2/CH4 ratios of 0.6-0.9, methane is completely converted, and the maximum space time yield (STY) of the reactor is about 1 L of CH4 per second per liter of reactor. A mathematical model for this process was developed. The results of modeling agree well with the experimental data. One possible application of the developed syngas generator in internal combustion engines is discussed.
CHEMICAL MICROREACTORS IN CATALYSIS
N.P. Belyaeva
Catal. Ind., 2 (2004) pp. 21-27.
The article is devoted to a new trend in the sphere of chemical synthesis: synthesis in the reactors of submillimetric dimensions named as "microreactors". They are characterized by an extremely great surface/volume ratio and exclusively high mass and heat transfer rates. Because of these properties, catalytic processes with participation of toxic and explosive substances may safely proceed in such microreactors. Highly-exothermal and highlyendothermic processes regulation is possible. The microreactors expand possibilities of kinetic studies and combinatorial catalysis. Examples of their application in catalysis are given.
CENTRIFUGAL FLASH-REACTOR FOR THERMO-SHOCK TREATMENT OF POWDER MATERIALS AT THE STAGES OF SYNTHESIS OF SUPPORTS AND CATALYSTS
V.I. Pinakov*, O.I. Stoyanovskii*, Yu.Yu. Tanashev, A.A. Pikarevskii*, B.E. Grinberg*, V.N. Dryab*, K.V. Kulik*, V.V. Danilevich, D.V. Kuznetsov*, V.N. Parmon (*Design-Technological Institute of Hydroimpulsive Engineering, Novosibirsk, Russia)
Catal. Ind., Special Issue (2004) pp. 60-67.
A concept of centrifugal thermo-shock treatment (activation) of powder materials over solid heat-carrier has been developed and the proper instrumentation of the process has been proposed. The centrifugal flash-reactor provides: heating of powders of 10-150 mm in size up to T = 100÷700 ° C with the rate >1000 degree/s; time of thermal treatment not more than 1,5 s; control of thermal treatment by changing the rotary speed and heat-carrier configuration, controllable flow of initial material in the range of 5-40 kg/h; removal of gaseous products, and quenching of solid products. Reactor is used for heat treatment of hydrargillite. According to data of physicalchemical analysis the product is characterized by high reactivity and can be used for preparation of alumina catalysts, supports, and other functional materials on the basis of γ-and η-Al2O3