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(NO_n)Cl_2−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 NO_n 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 La_1-xCa_xFeO_3-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 La_1-xCa_xFeO_3-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 La_1-xCa_xFeO_3-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 La_1-xCa_xFeO_3-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 La_1-xCa_xFeO_3-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 La_1-xCa_xFeO_3-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.

PROPANE CARBONYLATION ON SULFATED ZIRCONIA CATALYST AS STUDIED BY ¹³C MAS NMR AND FTIR SPECTROSCOPY

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 Mn^δ+) 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⁺/Mn^δ+ (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 CoO_x 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 CO_ads and NO_ads 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 O_ads atoms. When a mixed adsorbed CO_ads + NO_ads 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 CO_ads+NO_ads 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 Mo_xO_y (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 Mo_xO_y + complexes with the methyl radical were estimated to be D⁰(MoO_y⁺-CH₃) > 91.6 (y = 2, 3), D⁰(Mo₂O_y ⁺-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 O_αH (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 ¹⁶O_α by ¹⁸O_α. The stoichiometric ratio H₂ : O_α 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%(CuxMg_1–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 Ca_0.7Sr_0.3Fe_O3.0 and La_0.7Sr_0.3CoO_2.5(3.0) perovskites exhibited similar activities in the deep oxidation of UDMH, which were higher than the activity of Ca_0.7Sr_0.3FeO_2.5. A comparison between the selectivities of the conversion of fixed nitrogen, which is a constituent of UDMH, into nitrogen oxides SNO_xN 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