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:
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).
Visits of the specialists from the Boreskov Institute of Catalysis to foreign institutions in 2010
Austria | 32 | Germany | 47 | Saudi Arabia | 4 |
Azerbaijan | 13 | Hungary | 1 | Serbia | 2 |
Belarus | 3 | India | 1 | Singapore | 2 |
Belgium | 9 | Israel | 1 | Slovenia | 6 |
Brazil | 2 | Italy | 13 | Spain | 6 |
China | 19 | Japan | 7 | Sweden | 4 |
Czech Republic | 7 | Kazakhstan | 10 | Turkey | 7 |
Denmark | 3 | Netherlands | 8 | UAE | 4 |
Egypt | 2 | Poland | 4 | Ukraine | 7 |
Finland | 5 | Portugal | 1 | United Kingdom | 4 |
France | 23 | Republic of Korea | 1 | USA | 5 |
Visits of foreign specialists to the Boreskov Institute of Catalysis in 2010
Australia | 1 | Indonesia | 1 | Republic of Korea | 2 |
Austria | 1 | Italy | 2 | Saudi Arabia | 1 |
China | 21 | Japan | 1 | Spain | 2 |
France | 30 | Kazakhstan | 5 | Taiwan | 2 |
Germany | 3 | Mongolia | 1 | United Kingdom | 5 |
ndia | 2 | Netherlands | 7 | USA | 2 |
ITALY
The cooperation in the frame of the agreement between Russian Academy of Sciences (RAS) and National Council on the Scientific Research of Italy with The Istituto di Tecnologie Avanzate per l’Energia “Nicola Giordano” (CNR Institute of Advanced Energy Technologies “Nicola Giordano”), Messina – BIC, Novosibirsk on the Project “Materials with Enhanced Properties for Energy Conversion”. Coordinators: Prof. Yu. Aristov (BIC) and Prof. G. Restuccia (Istituto di Tecnologie Avanzate per l’Energia “Nicola Giordano”).
FRANCE
According to the agreement between RAS and CNRS BIC collaborates with the Institute de Recherches sur la Catalyse et l’Environnement de Lyon (Research Institute on Catalysis and Environment), Villeurbanne, in the frame of the Russian-French European associated Laboratory on Catalysis headed by Prof. V. Parmon and Dr. M. Lacroix. The Laboratory was established by an agreement signed December 6, 2004 in Moscow by RAS and CNRS. Four areas of research were identified:
INDIA
In the frame of RAS-DST Long Term Programme of cooperation in science and technology BIC collaborates with National Chemical Laboratory, Pune. Coordinators on the Program “Catalysis” are Prof. V. Parmon and Prof. S. Sivaram.
GERMANY
The cooperation in the frame of the agreement between RAS and German Scientific Research Society (GSRS) with
CHINA
The cooperation in the frame of Associated Research Laboratory which was established by an agreement signed December 4, 2004 by the Boreskov Institute of Catalysis and Heilongjiang University, Harbin. Chief Executive officers of Laboratory are: Prof. V. Bukhtiyarov, Prof. G. Echevsky (BIC) and Prof. Fu Hong-Gang, Prof. Wu Wei (Heilongjiang University) on the Project “Synthesis and Modification of ZSM-12 Zeolites. Zeolite ZSM-12 in Reaction of Naphthalene Alkylation with Methanol”.
COOPERATION IN THE FRAME OF PROJECTS FINANCED BY INTERNATIONAL FOUNDATIONS
CRDF Project
Carbon Nanoreactor for Solid-State Synthesis of Novel Nanoscale Materials Based on Nanocrystalline Oxides
Project Coordinators:
Prof. A. Volodin, Boreskov Institute of Catalysis, Novosibirsk, Russia
Prof. K.J. Klabunde, Kansas State University, Manhattan, Kansas, USA.
EUROPEAN COMMUNITY SIXTH FRAMEWORK PROGRAM
Co-Processing of Upgraded Bio-Liquids in Standard Refinery Units
Coordinator: Dr. Y. Solantausta, VTT Processes, Espoo, Finland
Partners:
Rijksuniversiteit Groningen, The Netherlands; Boreskov Institute of Catalysis, Novosibirsk,
Russia (Prof. V. Kirillov); Uhde Hochdrucktechnik GmbH, Germany; BTG Biomass Technology
Group BV, The Netherlands; University of Twente, The Netherlands; STFI-PACKFORSK AG,
Sweden; Institute of Wood Chemistry, Hamburg, Germany; Slovenian Institute of Chemistry,
Slovenia; Arkema SA, France; Helsinki University of Technology, Finland; ALMA Consulting
Group SAS, France; Centre National de la Recherche Scientifique, France; Chimar Hellas SA,
Greece; Albermarle Catalysts Company BV, The Netherlands; Metabolic Explorer, France; Shell
Global Solutions International, The Netherlands.
Non-Noble Catalysts for Proton Exchange Membrane Fuel Cell Anodes
Coordinator:
Dr. G. Tsotridis, Institute for Energy, Joint Research Centre, Petten, The Netherlands
Partners:
Technical University of Denmark, Lyngby, Denmark; Boreskov Institute of Catalysis,
Novosibirsk, Russia (Prof. V. Parmon, Dr. O. Taran); Southampton University, United
Kingdom; Technical University of Munich, Germany; Bavarian Center for Applied Energy
Research; Umicore, AG & Co KG, Germany.
Demonstration of SOFC Stack Technology for Operation at 600°C
Coordinator:
B. Rietveld, Energy Research Centre of The Netherlands, Petten, The Netherlands
Partners:
University St. Andrews, UK; HTceramix, Yverdon, Switzerland; Imperial College, UK;
Karlsruhe University, Germany; Oxford University, UK; University of Leoben, Austria;
Boreskov Institute of Catalysis, Novosibirsk, Russia (Prof. V. Sadykov); Technical University of
Denmark, Denmark; VTT Technical Research Centre of Finland, Finland;
Dalian Institute of Chemical Physics, China.
EUROPEAN COMMUNITY SEVENTH FRAMEWORK PROGRAM
Reforming of Crude Glycerin in Supercritical Water to Produce Methanol for Re-Use in
Biodiesel Plants
Coordinator: J. Vos, BTG BiomassTechnology Group BV, The Netherlands
Partners:
Acciona Servicios Urbanos, Spain; Boreskov Institute of Catalysis, Novosibirsk, Russia
(Prof. V. Kirillov); Rijksuniversiteit Groningen, The Netherlands; University of Maribor,
Slovenia; UHDE High Pressure Technologies GmbH, Germany; SPARQLE International BV,
The Netherlands.
Engine and Turbine Combustion of Bioliquids for Combined Heat and Power Production
Coordinator: J. Vos, BTG BiomassTechnology Group BV, The Netherlands
Partners:
AMO ZIL, Moscow, Russia; Aston University, Birmingham, UK; Boreskov Institute of Catalysis,
Novosibirsk, Russia (Prof. V. Kirillov); BTG Biomass Technology Group BV; Central
Scientific Automobile and Automotive Engines Institute, NAMI, Moscow, Russia; Encotech BV,
The Netherlands; University of Florence, Florence, Italy.
Oxidative Coupling of Methane Followed by Oligomerization to Liquids
Coordinator: G. Marin, Ghent University, Belgium
Partners:
Bayer Technology Service, Germany; Institute de Recherches sur la Catalyse et l’Environnement
de Lyon, Villeurbanne, France; Ruhr-Universität Bochum, TECHEM, Bochum, Germany;
Instituto de Technologia Quimica, Spain; Johnson Matthey, UK; SINTEF, Trondheim, Norway;
Linde Engineering, Germany; Cepsa R&D Center, Spain; Haldor Topsoe, Denmark;
Universitetet i Oslo, Oslo, Norway; University of Cambridge, UK; ALMA Consulting Group,
France; Boreskov Institute of Catalysis, Novosibirsk, Russia (V. Sadykov); INEOS, Belgium;
Institut fur Mikrotechnik Mainz Gmbh, Germany; Eni SpA, Italy.
INTERNATIONAL SCIENCE AND TECHNOLOGY CENTER (ISTC)
I.P. Glariozov*, G.M. Zhidomirov, M.I. Shilina*
(*Moscow Lomonosov State University, Moscow,
Russia)
Russ. Chem. Bull., 10 (2010) pp. 1821-1830.
Density functional PBE/TZ2p quantum chemical calculations of activated complexes and pathways of model catalytic transformations of propane under the action of aluminum chloride - cobalt chloride ionic bimetallic complexes were carried out. The formation of an intermediate with a broken C-C bond can occur on the cationic cluster CoAlCl4 + characterized by the strongest coordination of propane molecule. The activation barrier to the reaction is ΔG = 25.0 kcal⋅mol−1. Activation of alkane C-H bonds follows the alkyl pathway involving the formation of bimetallic alkyl complexes. The interaction of activated hydrocarbon fragments bound to transition metal atoms in cobalt-chloroaluminate clusters can result in alkane metathesis products (in this case, ethane and a polymetallic cluster containing an extended chain alkyl radical).
ACTIVATION OF MOLECULAR OXYGEN IN TRIFLUOROACETIC ACID
M.V. Vishnetskaya*, A.V. Vasin*, V.N. Solkan**, G.M. Zhidomirov, M.Ya. Mel’nikov*** (*Gubkin Russian State University of Oil and Gas, Moscow, Russia; **Zelinsky Institute of Organic Chemistry, Moscow, Russia; ***Moscow Lomonosov State University, Moscow, Russia)
Russ. J. Phys. Chem. A, 84(11) (2010) pp. 1905-1907.
The interaction of molecular oxygen with aqueous trifluoroacetic acid (TFA) led to an increase in pH. This effect was explained by a decrease in the concentration of the protonated CF3CO2H2+ and H3O+ species after oxygen was fed in the reactor. Quantumchemical calculations show that a radical pair can be formed in an activation-free exothermal reaction involving the radical residue of the acid, the CF3CO2H2+···3O2···CF3CO2 - peroxide radical, and the acid molecule in the CF3CO2 •···HOO• collision complex. It was assumed that the activation of molecular oxygen in aqueous TFA solutions, providing the activity of the system in oxidations of various organic and inorganic substrates, is related to the formation of peroxide radicals in them.
THE MECHANISM OF FORMATION OF THE HYDROPEROXYL RADICAL IN THE CF3COOH + 3O2 SYSTEM: A QUANTUM-CHEMICAL STUDY
V.N. Solkan*, G.M. Zhidomirov, M.Ya. Mel’nikov** (*Zelinsky Institute of Organic Chemistry, Moscow, Russia; **Moscow Lomonosov State University, Moscow, Russia)
Russ. J. Phys. Chem. B, 4(5) (2010) pp. 705-708.
Ab initio quantum-chemical calculations of the (CF3CO2H2+…3O2) and (CF3CO2-…3O2) complexes were performed by the MP2 method. It was found that these complexes were characterized by low complex formation energies, of 2.97 and 1.72 kcal/mol, respectively. According to the MP2(full)/6-311++G(d, p) calculation data, the bridge stabilization of oxygen by linking with both the CF3CO2H2+ cation and CF3CO2- anion is much more favorable energetically. A study of the potential energy surface of the joint molecular system (CF3CO2H2+…3O2…CF3CO2-) shows that proton experiences activationless transfer from the cation to the 3O2 molecule accompanied by electron transfer from the CF3COO- anion. An analysis of spin density distribution shows that two radicals are stabilized in the (CF3CO2….OOH….O=C(OH)CF3) complex in the triplet state observed on the potential energy surface.
ION-EXCHANGED BINUCLEAR Ca2Ox CLUSTERS, x=1-4, AS ACTIVE SITES OF SELECTIVE OXIDATION OVER MOR AND FAU ZEOLITES
A.V. Larin*, G.M. Zhidomirov, D.N. Trubnikov*, D.P. Vercauteren** (*Moscow Lomonosov State University, Moscow, Russia; **University of Namur, Namur, Belgium)
J. Comput. Chem., 31(2) (2010) pp. 421-430.
A new series of calcium oxide clusters Ca2Ox (x = 1-4) at cationic positions of mordenite (MOR) and faujasite (FAU) is studied via the isolated cluster approach. Active oxide framework fragments are represented via 8-membered window (8R) in MOR, and two 6R and 4R windows (6R+4R) possessing one common Si-O-Si moiety in FAU. Structural similarities between the Ca2Ox (8R) and Ca2Ox (6R+4R) moieties are considered up to x = 4. High oxidation possibilities of the Ca2O2 (nR) and Ca2O3 (nR) systems are demonstrated relative to CO, whose oxidation over the Ca-exchanged zeolite forms is well studied experimentally. Relevance of the oxide cluster models with respect to trapping and desorption of singlet dioxygen is discussed.
STRUCTURE OF CHLORINE ON Ag(111): EVIDENCE OF THE (3x3) RECONSTRUCTION
B.V. Andryushechkin*, V.V. Cherkez*,**, E.V. Gladchenko****, G.M. Zhidomirov, B. Kierren**, Y. Fagot-Revurat**, D. Malterre**, K.N. Eltsov*,*** (*International Joint Laboratory IMTAS, A.M. Prokhorov General Physics Institute, Moscow, Russia; **International Joint Laboratory IMTAS, Universitй H. Poincarй–Nancy, Vandoeuvre les Nancy, France; ***Moscow Institute of Physics and Technology, Moscow Region, Russia)
Phys. Rev. B, 81 (2010) 205434 (5 pages).
The structure of the chlorine induced reconstruction of Ag(111) has been studied by a combination of low-temperature scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density-functional theory (DFT). It was demonstrated that previously observed mysterious LEED pattern arises as a result of diffraction from a system of small Å) (15–30 triangular antiphase domains with a new (3x3) superstructure. In the author’s model supported by DFT calculations, within a (3x3) unit cell the upper silver layer reconstructs forming a couple of three-atom triangles placed in fcc and hcp sites of the substrate. Chlorine atoms occupy fourfold hollow sites between these triangles. The corner holes, which look like depressions in the STM images, are also occupied by chlorine atoms.
ON MECHANOCHEMICAL DIMERIZATION OF ANTHRACENE. DIFFERENT POSSIBLE REACTION PATHWAYS
V.M. Tapilin, N.N. Bulgakov, A.P. Chupakhin*, A.A. Politov**, A.G. Druganov*** (*Novosibirsk State University, Novosibirsk, Russia; **Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia; ***Novosibirsk Institute of Organic Chemistry, Novosibirsk, Russia)
J. Struct. Chem., 51(4) (2010) pp. 635-641.
Calculations of the anthracene crystal structure, 10% isotropic compression of the anthracene crystal and its two dimers linked not through the central atoms of central rings are performed in the density functional theory approximation. Linear lattice parameters a, b, c, interatomic distances, and bond angles coincide with those determined by single crystal X-ray diffraction and previously calculated for an isolated anthracene molecule. The parameter γ is different by 12°, which is due to a weak dependence of the lattice energy on γ (the energy of only a few kcal per mole is required to turn the lattice at this angle). The calculated lattice energy (15 kcal/mol) is close to the enthalpy of sublimation. Dimers of another configuration than those linked through the central atoms of central rings are less energetically favorable. The formation of dimers at high pressure and shear deformation of “sandwiches” composed of anthracene molecules located above each other is shown, and a two-step dimerization scheme is proposed.
TO MECHANOCHEMICAL DIMERIZATION OF ANTHRACENE. CRYSTALLINE PHENANTHRENE UNDER HIGH PRESSURE AND SHEAR CONDITIONS
A.A. Politov*, A.P. Chupakhin**, V.M. Tapilin, N.N. Bulgakov, A.G. Druganov*** (*Institute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia; **Novosibirsk State University, Novosibirsk, Russia; ***Novosibirsk Institute of Organic Chemistry, Novosibirsk, Russia)
J. Struct. Chem., 51(6) (2010) pp. 1064-1069.
Calculations at the density functional theory level show that for phenanthrene, unlike anthracene, stable dimeric structures are absent. A study of the absorption and photoluminescence spectra of crystalline phenanthrene under a pressure to 30 kbar and a simultaneous shear reveals reversible changes in the spectra: a shift of absorption bands and luminescence to the long wave region, a decrease in the intensity, and disappearance of the vibrational structure. Unlike anthracene, the dimerization (and other irreversible transformations) of phenanthrene under the simultaneous effect of high pressure and shear is not observed.
ELECTRONIC STRUCTURES OF MIXED IONIC-ELECTRONIC CONDUCTORS SrCoOx
V.M. Tapilin, A.R. Cholach, N.N. Bulgakov
J. Phys. Chem. Solids, 71(11) (2010) pp. 1581-1586.
Electronic structures of SrCoOx with x=3, 2.875 and 2.75 were calculated by DFT technique in SLDA approximation. Two kinds of oxygen vacancy ordering with energies of 0.22 and 0.01 eV lower in comparison with random vacancy distribution were
revealed. The transition between these ordered vacancy systems with the activation energy 0.34 eV can be a step in the ionic conductivity mechanism. The calculated ion charges, magnetic moments and electron density of states were used to analyze chemical bonding in the crystals. All calculated compounds have metal electronic conductivity.
WATER EFFECT ON THE ELECTRONIC STRUCTURE OF ACTIVE SITES OF SUPPORTED VANADIUM OXIDE CATALYST VOx/TiO2(001)
V.I. Avdeev, V.M. Tapilin
J. Phys. Chem. C, 114(8) (2010) pp. 3609-3613.
The interaction of water molecules with the reduced and fully oxidized surface sites of the supported vanadium oxide catalyst VOx/TiO2 has been investigated by the Periodic DFT method. It has been found that the molecular structures of the surface VOx species are radically altered when adsorbed water is involved in the redox cycle. Water dissociates spontaneously on the reduced vanadium sites forming the surface hydroxyl groups OH. The following reoxidation by gas-phase oxygen results in the formation of active sites O=VO2(OH) including both the Bronsted acid sites OH and the vanadyl oxygen V=O more reactive than on the dehydrated surface. Gas-phase oxygen, embedded on the surface under oxidation, does not take part in the formation of surface hydroxyl groups. The hydroxylation-hydration reaction path on the fully oxidized VOx/TiO2 surface has been calculated. It has been found that the recombination reaction of the two surface hydroxyl groups V-OH to form water with the following water desorption prevails over the reverse reaction of hydroxylation. In agreement with the experimental data it was concluded that lattice oxygen of surface vanadia species VOx, rather than gas-phase oxygen, undergoes isotope exchange with that of the adsorbed water.
SPIN-POLARIZED SELF-CONSISTENT-FIELD EQUATIONS FOR PAIRED ORBITALS
I.L. Zilberberg, S.F. Ruzankin
Phys. Rev. A, 82(4) (2010) 042505.
Unrestricted Hartree-Fock-like equations are proposed to find multiple spin-symmetry-broken states of the molecular systems. Developed equations are pseudo-eigenvalue-type equations for the Fock-type operators constructed in such a way to
include an effective field which makes different-spin orbitals biorthogonal. The eigenvectors of these operators are noncanonical Hartree-Fock orbitals becoming Lowdin-Amos-Hall paired (corresponding) orbitals after self-consistency is achieved. The eigenvalues of the modified Fock operators appear to be the energies of the paired orbitals. Because the paired orbitals do not follow the spatial symmetry of the molecular nuclear core, the equations allow one to obtain the broken symmetry states with relative ease as demonstrated for the model H6 hexagon molecule. For this molecule, the Čнћek-Paldus instability matrix analysis predicts the existence of three spin-symmetry-broken states. All these solutions are systematically achieved by the paired equations, unlike the standard unrestricted equations which basically converge to a single solution. The proposed approach is also valid for the density functional theory in which the spin-polarized Kohn-Sham equations might be transformed to paired equations.
PAIRED ORBITALS FOR DIFFERENT SPINS EQUATIONS
I.L. Zilberberg, S.F. Ruzankin
J. Comput. Chem., 31(1) (2010) pp. 84-89.
Eigenvalue-type equations for Lowdin-Amos-Hall spin-paired (corresponding) orbitals are developed to provide an alternative to the standard spin-polarized Hartree-Fock or Kohn-Sham equations in dealing with broken-symmetry (BS) states. To derive paired orbitals for different spins (PODS) equations there has been applied Adams-Gilbert “localizing” operator approach. The PODS equations contain different operators for different spins the eigen-vectors of which are paired orbitals associated with the same eigenvalue for each pair. Preliminary applications to simple systems show viability of this approach. Although the spectrum of possible applications of the PODS equations seems to be quite wide, they would be especially useful for obtaining and analyzing the S-z = 0 BS solutions for the systems with antiferromagnetic structure.
ADSORPTION SPECIES OF ETHYL BENZOATE IN MgCl2-SUPPORTED ZIEGLER-NATTA CATALYSTS. A DENSITY FUNCTIONAL THEORY STUDY
D.V. Stukalov, V.A. Zakharov, I.L. Zilberberg
J. Phys. Chem. C, 114(1) (2010) pp. 429-435.
Adsorption species of ethyl benzoate (EB) on the (104) and (110) MgCl2 surfaces have been studied within DFT. As a result, monodentate and bidentate complexes of EB were obtained on both the MgCl2 surfaces. The bidentate structures on the (104) MgCl2 surface proved to be stabilized by the decreased distance between neighboring adsorption sites (surface Mg cations). The different affinity of EB for the five-and four-coordinated Mg cations predicted was suggested to be the cause of changing the equilibrium shape of MgCl2 crystals upon growing in the presence of EB: EB chemisorption seems to stabilize the (110) MgCl2 surface to a greater degree as compared to the (104) MgCl2 surface. The influence of EB coordination mode on active site stereoselectivity is discussed.
KOOPMANS'S THEOREM IN THE RESTRICTED OPEN-SHELL HARTREE-FOCK METHOD: II. THE SECOND CANONICAL SET FOR ORBITALS AND ORBITAL ENERGIES
E.R. Davidson*, B.N. Plakhutin (*University of Washington, Seattle, Washington, USA)
J. Chem. Phys., 132(18) (2010) 184110.
A treatment of the validity of Koopmans’s theorem (KT) in the restricted open-shell Hartree– Fock (ROHF) method can be separated into two essentially different cases. The first of them involves the one-electron processes X→Xj± in which the spin state of an ion Xj± having a hole or an extra electron in the closed, open or virtual orbital ϕj is correctly described by a one-determinant wave function. This case was analyzed using different methods by Plakhutin et al. [J. Chem. Phys. 125, 204110 (2006)] and by Plakhutin and Davidson [J. Phys. Chem. A 113, 12386 (2009)]. In the present work the authors analyze more complex processes where the state of an ion cannot be described by a single determinant. An example of such processes is the removal of an alpha electron from the closed shell of a high-spin half-filled open-shell system X. For this case it is given a slightly generalized formulation of KT in both the “frozen” orbital approximation (i.e., within the canonical ROHF method) and the limited configuration
interaction approach for ionized systems. The authors also show that a simultaneous treatment of KT for all one-electron ionization processes possibly leads to the necessity of introducing in the canonical ROHF method two different sets of orbitals and two respective sets of orbital energies. The theory developed is compared with the previous formulations of KT in the restricted (ROHF) and unrestricted Hartree-Fock methods, and in the unrestricted density functional theory. The practical applicability of the theory is verified by comparing the KT estimates of the vertical ionization potentials in molecules O2 and NO2 with the respective experimental data.
C60 FULLERENE AS A PSEUDOATOM OF THE ICOSAHEDRAL SYMMETRY
A.V. Nikolaev*, B.N. Plakhutin (*Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow, Russia)
Russ. Chem. Rev., 79(9) (2010) pp. 729-755.
Unique features of the electronic structure and spectra of the C60 (Ih) fullerene and its ions related to the icosahedral symmetry are discussed. The so-called ′accidental′ degeneracy of terms in the open electron shells gN and hN (corresponding to four- and fivefold degeneracy of molecular orbitals, respectively) and the abnormal (′non-Bethe′) splitting of terms in the hN configuration are considered. The need to describe these terms arises in studies of ionized and excited states of the C60 molecule and its derivatives. A novel approach to the description of C60m± ions based on representation of the C60 (Ih) fullerene as a (pseudo)atom of icosahedral symmetry is considered in detail. The approach involves an expansion of the molecular orbitals of C60 in terms of the atomic orbitals centred at the origin (at the centre of the C60 molecule) and a multipole expansion of the electron repulsion. The energy spectra of the fullerene and C60m± ions, the magnetic moments and optical dipole transitions are considered. The results obtained are compared with those of ab initio calculations and with the available experimental data.
STABILIZATION OF Au AT EDGES OF BIMETALLIC PdAu NANOCRYSTALLITES
I.V. Yudanov, K.M. Neyman* (*University of Barcelona, Barcelona, Spain)
Phys. Chem. Chem. Phys., 12(19) (2010) pp. 5094-5100.
Density functional calculations were performed to study the distribution of Au atoms in bimetallic PdAu
nanoparticles. A series of Pd79–nAun clusters of truncated octahedral shape with different content of Au ranging from n = 1 to 60 was used to model such bimetallic nanosystems. Segregation of Au to the particle surface is found to be thermodynamically favorable. The most stable sites for Au substitution are located at the edges of the PdAu nanoclusters. The stabilization at the edges is rationalized by their higher flexibility for surface relaxation which minimizes the strain induced by larger atomic radius of Au as compared to Pd. This stabilization of Au at the edges indicates the possibility to synthesize PdAu particles with Pd atoms located mainly on the facets, and edges “decorated” by Au atoms. Such nanocrystallites are expected to exhibit peculiar catalytic properties and, being thermodynamically stable, should be prone to retaining their initial shape under catalytic conditions.
SIMULATION OF HETEROGENEOUS CATALYSTS AND CATALYTIC PROCESSES USING THE DENSITY FUNCTIONAL METHOD
V.A. Nasluzov*, E.A. Ivanova-Shor*, A.M. Shor*, I.V. Yudanov, N. Rцsch** (*Institute of Chemistry and Chemical Technology, Krasnoyarsk, Russia; **Technical University of Munich, Garching, Germany)
Kinet. Catal., 51(6) (2010) pp. 832-842.
The review is devoted to the use of high-level quantum-chemical calculations by the density functional method for the simulation of heterogeneous catalytic systems based on transition metals. The following problems are considered:
(1) the development of methods for simulating metal particles supported on the surfaces of ionic and covalent oxides; (2) the calculation of the properties of individual transition metal atoms and small clusters adsorbed on the surfaces of MgO, α-Al2O3, γ-Al2O3, and various modifications of SiO2 and in the pores of zeolites; (3) the mechanisms of hydrogen activation and acrolein hydrogenation on the metallic and partially oxidized surface of silver; and (4) the mechanism of formation of carbon residues upon the decomposition of methanol on nanosized Pd particles.
SMALL GOLD SPECIES SUPPORTED ON ALUMINA. A COMPUTATIONAL STUDY OF a-Al2O3(0001) AND y-Al2O3(001) USING AN EMBEDDED-CLUSTER APPROACH
V.A. Nasluzov*,**, T.V. Shulimovich*, A.M. Shor*, V.I. Bukhtiyarov, N. Rцsch***
(*Institute of Chemistry and Chemical Technology, Krasnoyarsk, Russia; **Siberian Federal University, Krasnoyarsk, Russia; ***Technical University of Munich, Garching, Germany)
Phys. Status Solidi B, 247(5) (2010) pp. 1023-1031.
The authors calculated the structures of and analyzed the bonding in adsorption complexes of small gold species Aun on a-Al2O3(0001), n = 1-6, and y-Al2O3(001), n = 1-5. A scalar-relativistic gradient-corrected density functional (DF) method was applied to cluster models of the support that were embedded in an extended elastic polarizable environment (EPE). The shortest Au—O distances, 204-211 pm, are consistent with extended X-ray adsorption fine structure (EXAFS) data for gold clusters on alumina surfaces. The calculated total adsorption energies increase with cluster nuclearity, up to n = 4, but drop for larger adsorbed species. In the gas phase, these small gold clusters exhibit a planar structure which they keep, oriented parallel to the surface, as adsorbates on a-Al2O3(0001). Unfavorable energy contributions result for larger clusters as their planar shape is notably distorted by the interaction with the support which amounts to 0.5-1.5 eV. On у-Al2O3(001), also the larger gold clusters retain their intrinsic planar structure as they adsorb oriented perpendicular to the surface. The corresponding adsorption energies are slightly smaller, 0.3-1.2 eV.
ON QUANTITATIVE DESCRIPTION OF METAL PARTICLES SIZE EFFECT IN CATALYTIC KINETICS
D.Yu. Murzin*, I.L. Simakova (*Еbo Akademi University, Turku/Еbo, Finland)
Kinet. Catal., 51(6) (2010) pp. 828-831.
Quantitative description for turnover frequency dependence on the metal cluster size for a two-step catalytic cycle was performed based on a thermodynamic approach, which accounts for changes of the chemical potential upon adsorption depending on the metal cluster size. Such analysis revealed a possibility for turnover frequency to exhibit a maximum. A very good
correspondence between calculated and experimental data in hydrogenation and decarboxylation reactions over palladium was achieved.
ELECTRONIC AND GEOMETRIC STRUCTURE OF ISOMERS OF NITRIC ACID. DFT QUANTUM CHEMICAL CALCULATIONS
I.I. Zakharov, O.I. Zakharova*, A.B. Tselishchev*, M.G. Loriya* (*V. Dal’ East Ukrainian National University, Severodonetsk, Ukraine)
J. Struct. Chem., 50(5) (2009) pp. 805-813.
Based on the B3LYP/6-311++G(3df,3pd) density functional method, quantum chemical calculations of the electronic structure, geometry, and thermodynamic parameters of eight isomers of nitric acid (three known isomers in the form of peroxynitrous acid ONOOH and five new isomers in the form of oxo-conformation OON(H)O) are presented in the work. The molecular structure of each isomer is characterized by a local minimum on the potential energy hypersurface of the HNO3 molecular system and corresponds to one of its stationary states. A theoretical study of the reactivity of nitric acid oxo-isomers characterized for the first time can provide adequate explanation for experiments on the autocatalytic use of nitric acid vapors in binding molecular nitrogen. The results obtained can be a direction for developing principally new methods to bind atmospheric nitrogen and activate methane, which are fundamental problems in chemical science and technology.
parameters of eight isomers of nitric acid (three known isomers in the form of peroxynitrous acid ONOOH and five new isomers in the form of oxo-conformation OON(H)O) are presented in the work. The molecular structure of each isomer is characterized by a local minimum on the potential energy hypersurface of the HNO3 molecular system and corresponds to one of its stationary states. A theoretical study of the reactivity of nitric acid oxo-isomers characterized for the first time can provide adequate explanation for experiments on the autocatalytic use of nitric acid vapors in binding molecular nitrogen. The results obtained can be a direction for developing principally new methods to bind atmospheric nitrogen and activate methane, which are fundamental problems in chemical science and technology.
V.P. Zhdanov
Chem. Phys. Lett., 492(1-3) (2010) pp. 77-81.
The kinetics of hydriding of metal nanoparticles in the generic case when the process is limited by diffusion of vacancies via the hydride shell was analysed. The treatment is focused on the role of lattice strain related to the misfit of the hydride and metal structures. In the absence of strain, the kinetics exhibits an initial fast stage followed by slowdown. Depending on the relative contribution of strain to the H-metal interaction in the ground and activated states for diffusion, the initial fast stage of the kinetics is either nearly not manifested or becomes shorter and occurs up to somewhat higher conversion.
OVERHEATING AND UNDERCOOLING DURING MELTING AND CRYSTALLIZATION OF METAL NANOPARTICLES
V.P. Zhdanov, M. Schwind*, I. Zoric*,
B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Physica E, 42(7) (2010) pp. 1990-1994.
In analogy with macroscopic metal samples, crystallization of metal nanoparticles may occur appreciably below the thermodynamic melting temperature, Tm (this temperature depends on the
particle size), while melting occurs at Tm. If the surface melting is suppressed, nanoparticles can be overheated during melting. These effects are described by using the classical nucleation theory and assuming that the nucleation starts at the particle corners or edges. The corresponding undercooling or overheating temperature intervals are found to be about 0.1 Tm for corners and 0.15 Tm for edges. These values are, respectively, two and one and a half times smaller than that for macroscopic samples. Under certain conditions, crystallization and melting can be controlled by the propagation of the front of a new phase. The corresponding temperature interval is found to be very narrow (about 0.02 Tm).
DIFFUSION-LIMITED KINETICS OF ADSORPTION OF BIOMOLECULES ON SUPPORTED NANOPARTICLES
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Colloids Surf., B, 76(1) (2010) pp. 28-31.
General equations have been derived describing the diffusion-limited kinetics of irreversible adsorption of biomolecules on nanoparticles, fabricated on a flat surface, in the case of no hydrodynamic flow in the solution. Under such conditions, the gradients in the concentration of biomolecules occur near the surface, while in more remote regions the gradients may or may not be significant depending on the surface concentration and
size of nanoparticles and the bulk concentration of biomolecules. The equations obtained make it possible to understand the conditions of realization of various regimes of adsorption.
APPARENT KINETICS OF HYDRIDING AND DEHYDRIDING OF METAL NANOPARTICLES
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Physica E, 42(5) (2010) pp. 1482-1486.
Hydriding and dehydriding kinetics of nanoparticles depend on the particle size. The calculations illustrate that the apparent (averaged over size) kinetics of an ensemble of particles can be dramatically different compared to those of single particles. Specifically, the authors analyze the hydriding kinetics, limited by diffusion of hydrogen atoms from the surface layer via the hydride shell to the metallic core, and the dehydriding kinetics limited by associative desorption of hydrogen from the surface layer. In both cases, the apparent kinetics are relatively slow in the later stage, their time scale for the given average size is much larger than that for a single particle of the same size, and some of the special features of the single-particle kinetics (e.g., the initial slowdown of dehydriding) can be partly or completely washed out. The scaling of the time scale of the kinetics with respect to the particle size, however, remains valid.
ON THE USE OF METAL NANOPARTICLES FOR ENHANCEMENT OF LIGHT ABSORPTION IN DYE-SENSITIZED SOLAR CELLS
V.P. Zhdanov
Physica E, 43(1) (2010) pp. 494-497.
Metal nanoparticles can be used to enhance light absorption in photovoltaic nanocrystalline dye-sensitized solar cells. The calculations scrutinizing this idea indicate, however, that the ratio of the rate of the induced power absorption by dyes, surrounding a nanoparticle, and the rate of the power dissipation by a nanoparticle is typically much lower than 0.5. Thus, this enhancement of light absorption seems to be practically inefficient.
SIMULATION OF DISSOCIATION OF DNA DUPLEXES ATTACHED TO THE SURFACE
V.P. Zhdanov, A. Gunnarsson*, F. Hook*
(*Chalmers University of Technology, Gцteborg, Sweden)
Central Eur. J. Phys., 8(6) (2010) pp. 883-892.
Monte Carlo simulations are presented of dissociation of duplexes formed of complementary single-stranded DNAs with one of the strands attached to the surface. To describe the transition from the bound state to the unbound state of two strands located nearby, a lattice model is used taking DNA base-pair interactions and comformational changes into account. The results obtained are employed as a basis for a more coarse-grained model including strand backward association and diffusion resulting in complete dissociation. The distribution of the dissociation time is found to be exponential. This finding indicates that the non-exponential kinetic features observed in the corresponding experiments seem to be related to extrinsic factors, e.g., to the surface heterogeneity.
SIZE-DEPENDENT KINETICS OF HYDRIDING AND DEHYDRIDING OF Pd NANOPARTICLES
Ch. Langhammer*, V.P. Zhdanov, I. Zoric*, B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Phys. Rev. Lett., 104(13) (2010) 135502.
Using a new indirect nanoplasmonic sensing method with subsecond resolution, hydriding and dehydriding kinetics of Pd nanoparticles in the size range 1.8-5.4 nm have been studied. Strong particle-size effects are observed. The scaling of the hydriding and dehydriding time scales satisfies power and power-exponential laws. The former (with an exponent of 2.9) is in perfect agreement with Monte Carlo simulations of diffusion-controlled hydriding kinetics. The latter is explained by the effect of surface tension on hydrogen desorption from the surface layer. The approach is generalizable to other reactant-nanoparticle systems.
SIZE-DEPENDENT HYSTERESIS IN THE FORMATION AND DECOMPOSITION OF HYDRIDE IN METAL NANOPARTICLES
Ch. Langhammer*, V.P. Zhdanov, I. Zoric*, B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Chem. Phys. Lett., 488(1-3) (2010) pp. 62-66.
Using a novel indirect nanoplasmonic sensing platform, hydrogen absorption/desorption isotherms have been measured in Pd nanoparticles with an average diameter from 1.8 to 8 nm at 30°C. The isotherms are fully reversible at relatively low and high pressures while at intermediate pressures there is hysteresis related to the hydride formation and decomposition. The hysteresis shrinks with decreasing particle size and becomes negligible for particles smaller than 2.5 nm. This feature has been explained in terms of a diminishing contribution of lattice strain to the free energy of hydride formation as the particle size goes down.
LSPR STUDY OF THE KINETICS OF THE LIQUID-SOLID PHASE TRANSITION IN Sn NANOPARTICLES
M. Schwind*, V.P. Zhdanov, I. Zoric*,
B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Nano Lett., 10(3) (2010) pp. 931-936.
Using the localized surface plasmon resonance as a probe in solid and liquid Sn nanoparticles of 107 nm diameter and 52 nm height, the authors have studied their kinetics of melting and freezing at temperature ramps and, for the first time, at fixed temperatures. During temperature ramps, the kinetics exhibit distinct hysteresis. The melting occurs near the bulk melting point while the freezing is observed at much lower temperatures so that the undercooling interval is similar to 130 K. The time scale of the freezing kinetics measured at different fixed temperatures rapidly decreases as the latter are lowered. All these findings have been quantitatively described by assuming the nucleation to occur on the edges of nanoparticles and employing the classical nucleation theory with the corresponding modifications.
PROTEIN ADSORPTION AND DESORPTION ON LIPID BILAYERS
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Biophys. Chem., 146(2-3) (2010) pp. 60-64.
The protein surface usually exhibits one or a few charged spots. If a lipid bilayer contains a significant amount of lipids with oppositely charged head groups, protein adsorption on a bilayer may be energetically favourable due to the protein-lipid electrostatic interaction. The specifics of this case are that the lipids are highly mobile and the protein adsorption is accompanied by the redistribution of lipids between the areas covered and not covered by protein. A kinetic model is presented illustrating that this effect is especially interesting if the fraction of the surface covered by charged lipids is relatively low. In this situation, with increasing protein coverage, the protein desorption rate constant rapidly increases while the adsorption rate constant drops, so that there is critical fraction of the area covered by protein. Adsorption above this fraction is hindered both kinetically and thermodynamically.
ADSORPTION OF PROTEINS ON A LIPID BILAYER
V.P. Zhdanov, B. Kasemo* (*Chalmers University of Technology, Gцteborg, Sweden)
Eur. Biophys. J. Biophys. Lett., 39(11) (2010) pp. 1477-1482.
In analysis of protein adsorption on a lipid bilayer, the protein surface is considered to contain one or a few charged spots, and the bilayer contains a significant amount of lipids with oppositely charged head groups. After adsorption, a folded protein is assumed to change its shape slightly due to the electrostatic attraction, so that one of the spots forms a flat contact with the oppositely charged lipid heads of the lipid bilayer. With realistic parameters, this model predicts that the contribution of electrostatic interactions to the protein adsorption energy per charged amino acid-lipid pair is 16-25 kJ/mol. Thus, a few (four or five) pairs is sufficient for irreversible adsorption.
HIERARCHICAL GENETIC NETWORKS AND NONCODING RNAs
V.P. Zhdanov
Chaos, 20(4) (2010) 045112.
In eukaryotic cells, many genes are transcribed into noncoding RNAs. Such RNAs may associate with mRNAs and inhibit their translation and facilitate degradation. To clarify what may happen in this case, a kinetic model was proposed describing the effect of noncoding RNAs on a mRNA-protein network with the hierarchical three-layer architecture. For positive regulation of the layers, the model predicts either bistability with a fairly narrow hysteresis loop or a unique steady state. For negative or mixed regulation, the steady state is found to be unique.
INTERPLAY OF NONCODING RNAs, mRNAs, AND PROTEINS DURING THE GROWTH OF EUKARYOTIC CELLS
V.P. Zhdanov
J. Exp. Theor. Phys., 111(4) (2010) pp. 699-705.
Numerous biological functions of noncoding RNAs (ncRNAs) in eukaryotic cells are based primarily on their ability to pair with target mRNAs and then either to prevent translation or to result in rapid degradation of the mRNA-ncRNA complex. Using a general model describing this scenario, it was shown that ncRNAs may help to maintain constant mRNA and protein concentrations during the growth of cells. The possibility of observation of this effect on the global scale is briefly discussed.
STOCHASTIC BURSTS IN THE KINETICS OF GENE EXPRESSION WITH REGULATION BY LONG NON-CODING RNAs
V.P. Zhdanov
JETP Letters, 92(6) (2010) pp. 410-415.
One of the main recent breakthroughs in cellular biology is a discovery of numerous non-coding RNAs (ncRNAs). The authors outline abilities of long ncRNAs and articulate that the corresponding kinetics may frequently exhibit stochastic bursts. For example, the authors scrutinize one of the generic cases when the gene transcription is regulated by competitive attachment of ncRNA and protein to a regulatory site. Monte Carlo simulations show that in this case one can observe huge long transcriptional bursts consisting of short bursts.
NON-CODING RNAs AND A LAYERED ARCHITECTURE OF GENETIC NETWORKS
V.P. Zhdanov
Central Eur. J. Phys., 8(6) (2010) pp. 864-872.
In eukaryotic cells, protein-coding sequences constitute a relatively small part of the genome. The rest of the genome is transcribed to non-coding RNAs (ncRNAs). Such RNAs form the cornerstone of a regulatory network that operates in parallel with the protein network. Their biological functions are based primarily on the ability to pair with and deactivate target messenger RNAs (mRNAs). To clarify the likely role of ncRNAs in complex genetic networks, it is presented and comprehensively analyzed a kinetic model of one of the key counterparts of the network architectures. Specifically, the genes transcribed to ncRNAs are considered to interplay with a hierarchical two-layer set of genes transcribed to mRNAs. The genes forming the bottom layer are regulated from the top and negatively self-regulated. If the former regulation is positive, the dependence of the RNA populations on the governing parameters is found to be often non-monotonous. Specifically, the model predicts bistability. If the regulation is negative, the dependence of the RNA populations on the governing parameters is monotonous. In particular, the population of the mRNAs, corresponding to the genes forming the bottom layer, is nearly constant.
EFFECT OF NON-CODING RNA ON BISTABILITY AND OSCILLATIONS IN THE mRNA-PROTEIN INTERPLAY
V.P. Zhdanov
Biophys. Rev. Lett., 5(2) (2010) pp. 89-107.
The feedbacks between the mRNA and protein synthesis may result in kinetic bistability and oscillations. Two generic models predicting bistability include, respectively, a gene with positive regulation of the mRNA production by protein and two genes with mutual suppression of the mRNA production due to negative regulation of the gene transcription by protein. The simplest model predicting oscillations describes a gene with negative regulation of the mRNA production by protein formed via mRNA translation and a few steps of conversion. The authors complement these models by the steps of non-coding RNA (ncRNA) formation and ncRNA-mRNA association and degradation. With this extension, the bistability can often be observed as well. Without and
with ncRNA, the biochemistry behind the steady states may be different. In the latter case, for example, ncRNA may control the mRNA population in the situations when this population is relatively small, and one can observe a switch in the mRNA, protein and ncRNA populations. The analysis of oscillatory kinetics of the mRNA-protein interplay shows that with ncRNA the oscillations may be observed in a wider range of parameters and the amplitude of oscillations may be larger.
ncRNA-MEDIATED BISTABILITY IN THE SYNTHESIS OF HUNDREDS OF DISTINCT mRNAS AND PROTEINS
V.P. Zhdanov
Physica A, 389(4) (2010) pp. 887-890.
The kinetics of gene expression can be bistable due to the feedback between the mRNA and protein formation. In eukaryotic cells, the interplay between mRNAs and proteins can be influenced by non-coding RNAs. Some of these RNAs, e.g., microRNAs, may target hundreds of distinct mRNAs. The model presented here shows how a non-coding RNA can be used as a mediator in order to involve numerous mRNAs and proteins into a bistable network.
STUDY OF n-HEXANE ISOMERIZATION ON Pt/SO4/ZrO2/Al2O3 CATALYSTS: EFFECT OF THE STATE OF PLATINUM ON CATALYTIC AND ADSORPTION PROPERTIES
M.D. Smolikov*, K.V. Kazantsev*, E.V. Zatolokina*, D.I. Kir’yanov*, E.A. Paukshtis, A.S. Belyi* (*Institute of Hydrocarbon Processing, Omsk, Russia)
Kinet. Catal., 51(4) (2010) pp. 584-594.
The state of surface Pt atoms in the Pt/SO4/ZrO2/Al2O3 catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al2O3 alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO4/ZrO2/Al2O3 superacid catalyst were used in this study. With the use of IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.
EFFECT OF CHROMIUM CONTENT ON THE PROPERTIES OF A MICROSPHERICAL ALUMINA–CHROMIUM CATALYST FOR ISOBUTANE DEHYDROGENATION PREPARED WITH THE USE OF A CENTRIFUGAL THERMAL ACTIVATION PRODUCT OF GIBBSITE
E.I. Nemykina, N.A. Pakhomov, V.V. Danilevich, V.A. Rogov, V.I. Zaikovsky, T.V. Larina, V.V. Molchanov
Kinet. Catal., 51(6) (2010) pp. 898-906.
The states of chromium in both promoted and unpromoted alumina–chromium catalysts with various chromium contents prepared with the use of a centrifugal thermal activation product of gibbsite were studied in detail. The presence of five chromium species was found in the catalysts of this type: two Cr6+ and three Cr3+ species. The concentration of each particular chromium species depends on the total chromium content of the catalyst. Based on the experimental data, the authors hypothesized that highly disperse Cr3+ particles, the formation of which was completed at a chromium content of ~7–9 wt %, are responsible for the catalytic activity of alumina– chromium samples in the reaction of isobutane dehydrogenation.
NONHEME MANGANESE-CATALYZED ASYMMETRIC OXIDATION. A LEWIS ACID ACTIVATION VERSUS OXYGEN REBOUND MECHANISM: EVIDENCE FOR THE “THIRD OXIDANT”
R.V. Ottenbacher, K.P. Bryliakov, E.P. Talsi
Inorg. Chem., 49(18) (2010) pp. 8620-8628.
The catalytic properties of a series of chiral nonheme aminopyridinylmanganese(II) complexes [LMnII(OTf)2] were investigated. The above complexes were found to efficiently catalyze enantioselective olefin oxidation to the corresponding epoxides with different oxidants (peroxycarboxylic acids, alkyl hydroperoxides, iodosylarenes, etc.) with high conversions and selectivities (up to 100%) and enantiomeric excesses (up to 79%). The effect of the ligand structure on the catalytic performance was probed. Epoxidation enantioselectivities were found to be strongly dependent on the structure of the oxidants (performic, peracetic, and m-chloroperbenzoic acids; tert-butyl and cumyl hydroperoxides; iodosylbenzene and iodosylmesitylene), thus bearing evidence that the terminal oxidant molecule is incorporated in the structure of the oxygen-transferring intermediates. High-valence electron-paramagnetic-resonance-active manganese complexes [LMnIV═O]2+ and [LMnIV(μ-O)2MnIIIL]3+ were detected upon interaction of the starting catalyst with the oxidants. The high-valence complexes did not epoxidize styrene and could themselves only contribute to minor olefin oxidation sideways. However, the oxomanganese(IV) species were found to perform the Lewis acid activation of the acyl and alkyl hydroperoxides or iodosylarenes to form the new type of oxidant [oxomanganese(IV) complex with a terminal oxidant], with the latter accounting for the predominant enantioselective epoxidation pathway in the nonheme manganese-catalyzed olefin epoxidations.
RESULTS OF NMR SPECTROSCOPIC STUDIES OF HYDROCARBON CONVERSIONS ON SOLID ACID CATALYSTS IN THE LAST 25 YEARS
A.G. Stepanov
Kinet. Catal., 51(6) (2010) pp. 854-872.
High-resolution solid-state NMR studies of hydrocarbon conversions on the surface of solid acid catalysts are overviewed. The results of identification of hydrocarbons adsorbed on solid acid catalysts are presented. Alkane activation and hydrocarbon conversion
mechanisms and the nature of reactive intermediates are discussed. It is demonstrated that NMR spectroscopy can be used not only in the in situ analysis of hydrocarbons on the catalyst surface, but also as a method for seeking new hydrocarbon conversion routes.
METAL-ALKYL SPECIES ARE FORMED ON INTERACTION OF SMALL ALKANES WITH GALLIUM OXIDE: EVIDENCE FROM SOLID-STATE NMR
A.A. Gabrienko, S.S. Arzumanov, A.V. Toktarev, A.G. Stepanov
Chem. Phys. Lett., 496(1-3) (2010) pp. 148-151.
C13 CP MAS NMR analysis of the products of the interaction of methane, ethane and propane with a-Ga2O3 or Ga-modified zeolite BEA at 523-623 K shows that dissociative adsorption of C1-C3 alkanes on the surface of gallium oxide or Ga-modified zeolite BEA results to the formation of Ga-methyl, Ga-ethyl and Ga-propyl species. This observation allows one to conclude that Ga-alkyls, rather than earlier suggested alkoxy species, could be the intermediates in small alkane dehydrogenation and aromatization on these catalysts.
PROPANE AROMATIZATION ON Zn-MODIFIED ZEOLITE BEA STUDIED BY SOLID-STATE NMR in situ
A.A. Gabrienko, S.S. Arzumanov, D. Freude*,A.G. Stepanov (*Leipzig University, Leipzig, Germany)
J. Phys. Chem. C, 114(29) (2010) pp. 12681-12688.
The conversion of propane (propane-1-13C and propane-2-13C) on Zn/H-BEA zeolite at 520-620 K has been studied by 1H and 13C (CP) MAS NMR. Propene adsorption complex with zinc sites (7t-complex) and o-allyl zinc species as intermediates have been identified in the course of propane conversion to aromatics. The mechanism leading to the formation of methane and ethane, which are constituents of an undesirable route in propane conversion, has been examined by kinetic modeling of the expected reaction network based on in situ 1H MAS NMR kinetic measurements of the reaction performance. The pathways for propane aromatization and hydrogenolysis have been proposed. Hydrogenolysis of propane has been concluded to occur with the involvement of both Brшnsted acid sites and Zn sites.
H/D EXCHANGE OF MOLECULAR HYDROGEN WITH BRONSTED ACID SITES OF Zn- AND Ga-MODIFIED ZEOLITE BEA
A.A. Gabrienko, S.S. Arzumanov, A.V. Toktarev, I.G. Danilova, D. Freude*, A.G. Stepanov (*Leipzig University, Leipzig, Germany)
Phys. Chem. Chem. Phys., 12(19) (2010) pp. 5149-5155.
Kinetics of hydrogen H/D exchange between Brшnsted acid sites of pure acid-form and Zn- or Ga-modified zeolites beta (BEA) and deuterated hydrogen (D2) has been studied by 1H MAS NMR spectroscopy in situ within the temperature range of 383–548 K. A remarkable increase of the rate of the H/D exchange has been found for Zn- and Ga-modified zeolites compared to the pure acid-form zeolite. The rate of exchange for Zn-modified zeolite is one order of magnitude higher compared to the rate for Ga-modified zeolite and two orders of magnitude larger compared to the pure acid-form zeolite. This promoting effect of metal on the rate of H/D exchange was rationalized by a preliminary dissociative adsorption of molecular hydrogen on metal oxide species or metal cations. The adsorbed hydrogen is further involved in the exchange with the acid OH groups located in vicinity of metal species. The role of different metal species in the possible mechanisms of the exchange with involvement of zeolite Brшnsted acid sites and metal species is discussed.
STRONG ACIDITY OF SILANOL GROUPS OF ZEOLITE BETA: EVIDENCE FROM THE STUDIES BY IR SPECTROSCOPY OF ADSORBED CO AND H1 MAS NMR
A.A. Gabrienko, I.G. Danilova, S.S. Arzumanov, A.V. Toktarev, D. Freude*, A.G. Stepanov
(*Leipzig University, Leipzig, Germany)
Microporous Mesoporous Mater., 131(1-3) (2010) pp. 210-216.
Acidic OH groups of acid-form and Zn and Ga-modified zeolite beta (BEA) have been characterized with 1H MAS NMR and by IR spectroscopy of adsorbed carbon monoxide. It is demonstrated that OH groups, which exhibit a vibration band at 3740 cm-1, reveal acidity, which is similar to that of the OH groups with the band at 3610 cm-1 according to the value of the low frequency shift of OH vibrations with adsorbed CO (ΔνOH/CO=300 cm-1). The IR band 3740 cm-1 corresponds to the signal at ca. 2.1 ppm in 1H MAS NMR spectrum. The OH groups with signal 2.1 ppm are involved in H/D exchange with methane-d4 similar to acidic OH groups
with the signals 4.0-5.1 ppm. The signals at 2.1 ppm in 1H MAS NMR and at 3740 cm4 in IR are attributed to the strongly acidic silanol groups of the faulted structure of the zeolite. The silanols with the signals at 1.8 ppm and 3745 cm4 are weakly acidic (AvOH/CO=85 cm4) and are not involved in the H/D exchange. Loading of the zeolite with Zn affords a notable decrease of the concentration of strongly acidic SiOHAl groups, whereas the quantity of these groups does not decrease upon loading the zeolite with Ga.
THE “ALKYL” AND “CARBENIUM” PATHWAYS OF METHANE ACTIVATION ON GA-MODIFIED ZEOLITE BEA: 13C SOLID-STATE NMR AND GC-MS STUDY OF METHANE AROMATIZATION IN THE PRESENCE OF HIGHER ALKANE
M.V. Luzgin, A.A. Gabrienko, V.A. Rogov, A.V. Toktarev, V.N. Parmon, A.G. Stepanov
J. Phys. Chem. C, 114(46) (2010) pp. 21555-21561.
By using 13C solid-state NMR spectroscopy and GC-MS analysis, the activation of methane and co-aromatization of methane and propane have been monitored on gallium-modified zeolite BEA at 573-823 K. A noticeable degree involvement of the 13C-label from methane-13C into the aromatic reaction products (benzene, toluene) has been demonstrated. The major intermediate of the methane activation represents gallium-methyl species, which are formed by methane dissociative adsorption on Ga2O3 species of the zeolite. The minor species of methane activation, Ga-methoxy groups, provide the involvement of methane into aromatics by the methylation of aromatic molecules, which are generated exclusively from propane, by the mechanism of electrophilic substitution. Ga-methyl species can serve as methylating nucleophilic agent for the reaction of nucleophilic substitution with participation of aromatic molecules, which contain the electron-withdrawing substitutes.
CARBONYLATION OF DIMETHYL ETHER ON SOLID Rh-PROMOTED Cs-SALT OF KEGGIN 12-H3PW12O40: A SOLID-STATE NMR STUDY OF THE REACTION MECHANISM REACTIVITY
M.V. Luzgin, M.S. Kazantsev, G.G. Volkova, W. Wang*, A.G. Stepanov (*Lanzhou University, Gansu, People’s Republic of China)
J. Catal., 278(2) (2010) pp. 353-361.
The carbonylation of dimethyl ether (DME) with carbon monoxide on Rh-promoted cesium salt of 12-tungstophosphoric acid, Rh/Cs2HPW12O40 (HPA), has been studied with 13C solid-state NMR. The bifunctional character of Rh/Cs2HPW12O40 catalyst in halide-free carbonylation of DME has been directly demonstrated. The activation of the C-O bond of DME proceeds on Brшnsted acid sites of HPA with the formation of the methyl group attached to the surface of HPA (methoxy species), whereas the role of rhodium consists in trapping carbon monoxide from gaseous phase and a transfer of CO to the center of DME activation, acidic OH-group of the catalyst, in the form of rhodium-carbonyls. The lattice of Cs2HPW12O40 makes it possible to locate these two different active centers in close proximity to each other, e.g., on two adjacent oxygen atoms, terminal and bridging, of one Keggin anion, thus facilitating the insertion of carbon monoxide from rhodium carbonyl into the C-O bond of methoxy-group to produce the acetate group bound to the Keggin anion. The latter offers finally methyl acetate under the interaction with DME, the intermediate surface methoxy-groups being restored.
EFFECT OF Pt NANOPARTICLE SIZE ON THE SPECIFIC CATALYTIC ACTIVITY OF Pt/SiO2 AND Pt/TiO2 IN THE TOTAL OXIDATION OF METHANE AND n-BUTANE
A.Yu. Stakheev*, A.M. Gololobov*, I.E. Beck, G.O. Bragina*, V.I. Zaikovsky, A.B. Ayupov, N.S. Telegina*, V.I. Bukhtiyarov (*Zelinsky Institute of Organic Chemistry, Moscow, Russia)
Russ. Chem. Bull., 9 (2010) pp. 1713-1719.
The dependence of the specific catalytic activity (Asp ) of the catalysts Pt/SiO2 and Pt/TiO2 in the total oxidation of CH4 and n-C4H10 on the Pt nanoparticle size (in the range from 1 to 4 nm) was studied. The specific catalytic activity increases with an increase in the platinum nanoparticle size, indicating that the total oxidation is a structure-sensitive reaction. The structure sensitivity depends on the size of an oxidized molecule: it increases sharply on going from CH4 to n-C4H10. The support also exerts a considerable effect
on the Asp value: in the oxidation of both CH4 and C4H10 the specific catalytic activity for the catalysts Pt/TiO2 is 3–4 times that for Pt/SiO2.
OXYGEN SPECIES ON THE SILVER SURFACE OXIDIZED BY MW-DISCHARGE: STUDY BY PHOTOELECTRON SPECTROSCOPY AND DFT MODEL CALCULATIONS
L.S. Kibis, V.I. Avdeev, S.V. Koshcheev, A.I. Boronin
Surf. Sci., 604(13-14) (2010) pp. 1185-1192.
A polycrystalline silver surface has been studied by synchrotron radiation photoelectron spectroscopy after deep oxidation by microwave discharge in an O2 atmosphere. Oxidized structures with high oxygen content, AgOx with x > 1, have been found on the silver surface after oxidation at 300–400 K. The line shapes observed in the O1s spectra were decomposed into five components and indicated that complex oxidized species were formed. An analysis of the oxidized structures with binding energies, Еb(O1s), greater than 530 eV pointed to the presence of both Ag–O and O–O bonds. A detailed experimental study of the valence band spectra in a wide spectral range (up to 35 eV) have been carried out, which has allowed to register the multicomponent structure of spectra below Ag4d band. These features were assigned to the formation of Ag–O and O–O bonds composed of molecular (associative) oxygen species. DFT model calculations showed that saturation of the defect oxidized silver surface with oxygen leads to the formation of associative oxygen species, such as superoxides, with electrophilic properties and covalent bonding. The high stability of oxygen-rich silver structures, AgOx, can be explained by the formation of small silver particles during the intensive MW oxidation, which can stabilize such oxygen species.
THE INVESTIGATION OF OXIDIZED SILVER NANOPARTICLES PREPARED BY THERMAL EVAPORATION AND RADIO-FREQUENCY SPUTTERING OF METALLIC SILVER UNDER OXYGEN
L.S. Kibis, A.I. Stadnichenko, E.M. Pajetnov, S.V. Koshcheev, V.I. Zaikovsky, A.I. Boronin
Appl. Surf. Sci., 257(2) (2010) pp. 404-413.
The investigation of oxidized silver nanoparticles by the photoemission (XPS, UPS) and HRTEM methods was performed. The nanoparticles of oxidized silver were obtained in the vacuum chamber
by two methods of synthesis: thermal evaporation of silver nanoparticles followed by transferring in convective gas flow and sputtering of oxidized clusters under the action of plasma. Both methods indicated that oxygen interaction with silver nanoparticles depends strongly on its size. It was shown that the chemical bonding of oxygen species stabilized on small particles differs from the oxygen species adsorbed on bulk silver surfaces (monocrystals, foils and large particles). The low charged oxygen with molecular type of bonding stabilizes on particles of size approximately 5 nm and smaller. Increasing particle size leads to the dissociation of molecular oxygen species and the formation of strongly charged oxygen composed of oxide nanoparticles like Ag2O or AgO type. The presence of extended defects in the microdomain large nanoparticles facilitates the formation of Ag2O or AgO layers covering metallic nanosilver.
INVESTIGATION OF ACTIVE METAL SPECIES FORMATION IN Pd-PROMOTED SULFATED ZIRCONIA ISOMERIZATION CATALYST
O.B. Belskaya*, I.G. Danilova, M.O. Kazakov*, T.I. Gulyaeva*, L.S. Kibis, A.I. Boronin, A.V. Lavrenov*, V.A. Likholobov* (*Institute of Hydrocarbons Processing, Omsk, Russia)
Appl. Catal., A, 387(1) (2010) pp. 5-12.
The state of palladium in Pd/SO42-–ZrO2 (Pd/SZ) isomerization catalyst was investigated by the temperature-programmed reduction (TPR), chemisorption technique, infrared spectroscopy of adsorbed carbon monoxide (FTIRS), X-ray photoelectron spectroscopy (XPS), diffuse-reflectance UV–vis spectroscopy (UV–vis DRS), and benzene hydrogenation as a test reaction. It has been stated that reduction temperature has a great impact on the metal function of Pd-promoted sulfated zirconia catalyst. Metal centers are formed at about 30–70°C and characterized by high palladium dispersion and activity in benzene hydrogenation. At temperatures above 200 °C, intensive sulfate decomposition occurs and products of sulfate reduction poison the metal function of the catalyst. According to XPS and FTIRS study, palladium particles in the poisoned samples are only partly oxidized, but the main part is presented by metallic phase without large amount of PdS. Reduction of Pd-containing catalyst at 150 °C (instead of 250°C) leads to higher conversion and 2,2-dimethylbutane yield in acid-catalyzed reaction of
n-hexane isomerization. Higher isomerization activity in this case is provided by prevention of active sulfate species decomposition due to the capability of palladium metallic particles formation at low reduction temperatures.
AN ACTIVE PHASE TRANSFORMATION ON SURFACE OF Ni-Au/Al2O3 CATALYST DURING PARTIAL OXIDATION OF METHANE TO SYNTHESIS GAS
T.P. Maniecki*, A.I. Stadnichenko, W. Maniukiewicz*, K. Bawolak*, P. Mierczyński*, A.I. Boronin, W.K. Jozwiak*
(*Technical University of Lodz, Lodz, Poland)
Kinet. Catal., 51(4) (2010) pp. 573-578.
It was studied the influence of gold addition on physico-chemical properties and catalytic activity of bimetallic Ni-Au/Al2O3 catalyst in partial oxidation of methane (POM). The reduction behavior in hydrogen, XRD crystal structure, XPS spectra and POM catalytic activity were investigated. The reduction of Ni-Au catalyst is a prerequisite condition to catalyze POM reaction. The formation of Ni-Au alloy during high temperature reduction in hydrogen and also in the conditions of POM reaction was experimentally proved. The addition of gold to Ni/Al2O3 system improves catalyst stability and activity in POM reaction.
FeAl12-KEGGIN TYPE CATION AS AN ACTIVE SITE SOURCE FOR Fe,Al-SILICA MESOPOROUS CATALYSTS
M.N. Timofeeva, M.E. Malyshev, V.N. Panchenko, A.N. Shmakov, A.G. Potapov, M.S. Melgunov
Appl. Catal., B, 95(1-2) (2010) pp. 110-119.
Iron-containing mesoporous mesophase materials Fe,Al-MMM-2 have been synthesized according to a sol-mesophase route under mild acidic conditions (pH 2.3–4.4) using Keggin type cation
[FeAl12O4(OH)24(H2O)12]7+ (FeAl127+) as Al and Fe
sources. Effect of pH of the synthetic solution on structural and physicochemical properties of Fe,Al-MMM-2 has been evaluated by means of small-and wide-angle XRD, FTIR, DR-UV–vis, and N2-adsorption/desorption analysis. It has been established that deviation of stability of FeAl127+ cation at various pH determines Al/Fe ratio in the resulting material as 12/1 (material synthesized at pH 4.4), and 6/1 (pH 2.4 and 3.3). Correlation between incorporation of Al and Fe in different forms and resulting materials texture is discussed.
Fe,Al-MMM-2 materials have been tested as catalysts for wet phenol oxidation with H2O2. Insertion of Al species into the framework of the silicate matrix increases the activity comparing to a reference Fe,Al-pillared clay due to both higher surface acidity and lower diffusion limitations that correspond to Fe,Al-MMM-2.
A ‘DOUBLE PEAK’ CATALYTIC ACTIVITY OF NANO-SIZED GOLD SUPPORTED ON TITANIA IN THE GAS-PHASE SELECTIVE OXIDATION OF ETHANOL
O.A. Simakova, V.I. Sobolev, K.Yu. Koltunov, B. Campo*, A.-R. Leino**, K. Kords**, D.Yu. Murzin* (*Abo Akademi University, Turku, Finland; **University of Oulu, Oulu, Finland)
ChemCatChem, 2(12) (2010) pp. 1535–1538.
Au/TiO2, in contrast to Au supported on silica and alumina, shows “double-peak” catalytic activity in partial oxidation of ethanol to acetaldehyde by molecular oxygen. The additional low-temperature peak probably corresponds to the specific participation of oxygen generated on Au/TiO2 surface under mild reaction conditions.
SULFATED ALUMINA AND ZIRCONIA IN ISOBUTANE/BUTENE ALKYLATION AND n-PENTANE ISOMERIZATION: CATALYSIS, ACIDITY, AND SURFACE SULFATE SPECIES
M.Yu. Smirnova, A.V. Toktarev, A.B. Ayupov, G.V. Echevsky
Catal. Today, 152(1-4 sp. issue) (2010) pp. 17-23.
The catalytic behavior of sulfated alumina (SA) and zirconia (SZ) was compared for two acid-catalyzed reactions, i.e., isobutane/butene alkylation and isomerization of n-pentane. For the alkylation reaction, the SZ catalyst gave a higher C5+ alkane yield and much lower selectivity for trimethylpentanes (TMPs) at 2 h TOS. However, TMPs selectivity was comparable for both catalysts at 5.5 h TOS. For the isomerization, high n-pentane conversion was obtained on SZ at the reaction temperature of 100°C when SA had no activity. Surface sulfate species were identified by IR spectroscopy. The acidity of sulfated oxides was compared by IR spectroscopy using pyridine and carbon monoxide as probe molecules and TPD-MS of ammonia. An effort was made to explain the difference between catalytic behavior of two sulfated oxides in terms of acidity, the nature of surface sulfate species and the formation of hydride species.
THE EFFECT OF SUPPORT PROPERTIES ON THE ACTIVITY OF Pd/C CATALYSTS IN THE LIQUID-PHASE HYDRODECHLORINATION OF CHLOROBENZENE
V.I. Simagina, O.V. Netskina, E.S. Tayban, O.V. Komova, E.D. Grayfer, A.V. Ishchenko, E.M. Pajetnov
Appl. Catal., A, 379(1-2) (2010) pp. 87-94.
The activity of palladium catalysts prepared using active carbons (AG-2000, MeKS) and Sibunit type carbon in the liquid-phase hydrodechlorination of chlorobenzene has been studied. The use of AG-2000 activated carbon prepared from coal raw material provided the highest initial activity of the catalyst (9.4 molC6H5Cl/molPd min) for the catalyst with particle size of 0.08–0.1 mm which not reduced within next 4 cycles. However, this activity cannot be explained only on the basis of support texture characteristics. From results of chemical analysis as well as X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR TEM) data the high activity of the Pd/AG-2000 catalyst is explainable by the presence on the surface of the initial activated carbon of oxygen-containing compounds of iron, aluminum, silicon, calcium and magnesium. The overall ash content of the activated carbon was 11.9 wt.%. It can be assumed that the oxide compounds of iron act as anchoring centers for palladium, and that oxide containing impurities may interact with HCl decreasing deactivation. The experimental data of this work has shown that the main contribution to the Pd/AG-2000 catalyst activity is made by the palladium particles with a size of 3 nm and higher which remain stable under the aggressive conditions of the chlorobenzene hydrodechlorination process.
COPPER-CERIUM OXIDE CATALYSTS PREPARED BY THE PECHINI METHOD FOR CO REMOVAL FROM HYDROGEN-CONTAINING MIXTURES
D.I. Potemkin, P.V. Snytnikov, V.P. Pakharukova, G.L. Semin, E.M. Moroz, V.A. Sobyanin
Kinet. Catal., 51(1) (2010) pp. 119-125.
A series of copper–cerium oxide catalysts was prepared by the Pechini method, and their physico-chemical and catalytic properties in CO oxidation in hydrogen-containing gas mixtures were studied. The method chosen for catalyst preparation yields finely dispersed copper and cerium oxides in the catalyst.
MECHANISM OF THE OXYGEN INVOLVEMENT IN NICOTINIC ACID FORMATION UNDER β-PICOLINE OXIDATION ON V-Ti-O CATALYST
Yu.A. Chesalov, E.V. Ovchinnikova, G.B. Chernobay, G.Ya. Popova, T.V. Andrushkevich
Catal. Today, 157(1-4) (2010) pp. 39-43.
Mechanism of the oxygen involvement in nicotinic acid formation under β-picoline oxidation on vanadia-titania catalyst was studied by in situ FTIR spectroscopy and kinetic method in temperature range of 120–300°C. The formation of nicotinic acid proceeds via a consecutive transformation of the surface carbonyl-like and carboxylate complexes stabilized at reduced vanadium. Catalyst oxygen includes in formation of these complexes. Carboxylate is a direct precursor of nicotinic acid, it turns into nicotinic acid in the presence of the gas-phase oxygen in joint step of catalyst reoxidation – acid desorption. Significant concentration ratio of oxygen to β-picoline (CO2:CβP > 16:1) is necessary to effective running reaction. This factor can be explained by the reaction mechanism. The variety of oxygen functions and of oxygen species require the maximum oxidized state of the catalyst and explain the necessity of a high oxygen excess in the reaction mixture.
KINETICS OF FORMALDEHYDE OXIDATION ON V-Ti-O CATALYST
E.V. Danilevich, G.Ya. Popova, I.A. Zolotarskii, An. Yermakova, T.V. Andrushkevich
Catal. Ind., 2(4) (2010) pp. 320-328.
The heterogeneous catalytic oxidation of formaldehyde in the gas phase may be considered as an alternative to the multistep liquid phase synthesis of formic acid. Monolayer vanadia–titania catalysts are active and selective in the oxidation of formaldehyde to formic acid. Detailed investigation of kinetics of formaldehyde oxidation over a monolayer vanadia– titania catalyst was carried out. It was established that by-products are formed via a consecutive–parallel reaction network. CO2 results from formaldehyde oxidation via parallel pathways and from formic acid overoxidation via consecutive pathway; CO is produced from the formic acid via consecutive pathway. It was shown that oxygen and water accelerate formic acid formation and that water retards CO formation. Based on experimental data, a kinetic model of formaldehyde oxidation was developed. The kinetic model was used in the mathematical simulation of the formaldehyde
oxidation process and in the determination of dynamic and design parameters of the reactor. Formic acid production by the gas phase oxidation of formaldehyde is unique and does not have any analogue. As opposed to conventional technologies, it is energy saving, environmentally friendly, and technologically simple. An enlarged scale pilot plant using this technology is under construction.
EXPERIMENTAL STUDY OF INTERMEDIATES AND WAVE PHENOMENA IN CO OXIDATION ON PLATINUM METAL (Pt, Pd) SURFACES
V.V. Gorodetsky, A.V. Matveev, A.A. Brylyakova
Kinet. Catal., 51(6) (2010) pp. 873-884.
The mechanism of catalytic CO oxidation on Pt(100) and Pd(110) single-crystal surfaces and on Pt and Pd sharp tip (~103 Е) surfaces has been studied experimentally by temperature-programmed reaction, temperature desorption spectroscopy, field electron microscopy, and molecular beam techniques. Using the density functional theory the equilibrium states and stretching vibrations of oxygen atoms adsorbed on the Pt(100) surface have been calculated. The character of the mixed adsorption layer was established by high resolution electron energy loss spectroscopy—molecular adsorption (O2ads, COads) on Pt(100)-hex and dissociative adsorption (Oads, COads) on Pt(100)-(1 Ч 1). The origin of kinetic self-oscillations for the isothermal oxidation of CO in situ was studied in detail on the Pt and Pd tips by field electron microscopy. The initiating role of the reversible phase transition (hex) ↔ (1 Ч 1) of the Pt(100) nanoplane in the generation of regular chemical waves was established. The origination of self-oscillations and waves on the Pt(100) nanoplane was shown to be caused by the spontaneous periodical transition of the metal from the low-active state (hex) to the highly active catalytic state (1 Ч 1). A relationship between the reactivity of oxygen atoms (Oads) and the concentration of COads molecules was revealed for the Pd(110) surface. Studies using the isotope label 18Oads demonstrated that the low-temperature formation of CO2 at 150 K is a result of the reaction of CO with the highly reactive state of atomic oxygen (Oads). The possibility of the low-temperature oxidation of CO via interaction with the so-called “hot” oxygen atoms (Ohot) appearing on the surface at the instant of dissociation of O2ads molecules was studied by the molecular beam techniques.
KINETICS OF THE H218O/H216O ISOTOPE EXCHANGE OVER VANADIA-TITANIA CATALYST
E.M. Sadovskaya, V.B. Goncharov, Yu.K. Gulyaeva, G.Ya. Popova, T.V. Andrushkevich
J. Mol. Catal. A: Chem., 316(1-2) (2010) pp. 118-125.
Study of oxygen exchange between vanadia-titania catalyst, H2O and O2 has been performed in isothermal (200°C) and thermo programmed (50-500°C) conditions. Experiments using H218O, 18O2 and monolayer vanadia-titania catalyst placed to the plug-flow reactor were carried out. Significant values of the rate of isotope exchange between O2 and the catalyst were observed at T > 450°C, but catalyst reduction accompanied oxygen desorption into gas phase proceeded in this case. Unlike dioxygen, water can exchange quite readily its oxygen atoms with vanadia-titania catalyst even at room temperature. Surface vanadium sites coordinating the OH group show the highest activity in the oxygen exchange with water. The rate constant of oxygen exchange between adsorbed water molecule and V-OH is ca. 0.5 s-1 at 200°C, with the activation energy close to zero. The rate of oxygen exchange with dehydrated vanadium complexes V-O-V and V=O is much lower. The rate
constant of this exchange is ca. 10-3 s-1 at 200°C, with the activation energy of ca. 70 kJ/mol. The interaction of adsorbed water with VOx species results in their slow hydrolysis to form the V-OH groups (characteristic time ca. 104 s), which recombination underlies the isotope exchange.
LIQUID PHASE HYDROAMINATION OF CYCLOHEXANONE
D.P. Ivanov, K.A. Dubkov, D.E. Babushkin, L.V. Piryutko, S.V. Semikolenov
Russ. Chem. Bull., 10 (2010) pp. 1896-1901.
Activity and selectivity of supported Ni, Pt, and Pd catalysts were studied in the liquidphase reductive amination of cyclohexanone at temperatures ranging from 100 to 150°C. The catalyst 20% Ni/SiO2 is most active and selective providing a maximum yield of cyclohexylamine. The influence of the reaction conditions on the parameters of the catalytic process was studied. A detailed analysis of the reaction products was carried out using 13C NMR spectroscopy and gas chromatography coupled with mass spectrometry (GC-MS). This made it possible to refine the reaction mechanism and to identify a new by-product earlier unknown in the literature