G. V. Antoshin

Reduction behavior and metathesis activity of WO3Al2O3 catalysts: I. An XPS investigation of WO3Al2O3 catalysts

The reduction of WO3Al2O3 catalysts with 7–23 wt% WO3 and of pure tungsten compounds was studied by XPS. In the pure compounds, W(VI) is reduced to the metal via W(V) and W(IV). An additional intermediate observed only in WO3 may be W(II) or W(IV) engaged in a particular interaction. In the reduction of Al2(WO4)3 a stabilization of W(VI) and W(IV) relative to Al-free samples is observed at high reduction temperatures. On the Al2O3 support the reduction of W(VI) starts at substantially higher temperatures than that in pure compounds. The stabilization is highest at low WO3 content, where the severe conditions required for W(VI) reduction lead to the direct formation of metallic W. At WO3 loadings near the theoretical monolayer capacity of the Al2O3 support, the lower temperatures of reduction permit the detection of W(IV) as an intermediate. Metallic W on Al2O3 exhibits a negative XPS shift relative to the bulk metal.

The state of platinum in high-silica zeolites and its catalytic activity in ethane and propane aromatization

Abstract The catalytic properties of Pt-containing high-silica zeolites in the aromatization of lower alkanes and the XPS spectra of these catalysts have been investigated. Both the electronic states of Pt and catalytic activity depended strongly on the pre-treatment conditions and changed in the course of the reaction. The development of the catalytic activity observed during successive catalytic runs in the pulse mode was accompanied by an increase in positive charge on highly dispersed metallic clusters located in the vicinity of acidic OH groups of zeolite. The Ptγ + centres in combination with acidic sites are likely to be responsible for ethane and propane transformations into aromatics over Pt-containing-high silica zeolites.

Reduction and aromatization activity of chromia-alumina catalysts: II. An XPS investigation of chromia-alumina catalysts

Abstract Chromia-alumina catalysts with 1.8 to 20 wt% Cr 2 O 3 , including samples containing additional elements as K, Pt, and Re, were reduced in H 2 in the 773–923 K temperature range at atmospheric pressure and investigated by X-ray photoelectron spectroscopy. In the Cr 2 p spectra of oxidized samples, Cr 6+ and Cr 3+ were detected. While Cr 6+ was rapidly transformed to Cr 3+ in the initial reduction phase a new chromium signal emerged after longer exposure times. This signal representing the product of Cr 3+ reduction was ascribed to highly dispersed zerovalent chromium with metallic band structure not formed, subject to a stabilization by the support. Signals that could be attributed to Cr 2+ and Cr 5+ were not found in this study. With regard to catalytic experiments reported earlier, the aromatization activity of chromia-alumina catalysts was ascribed to Cr 3+ coordinatively unsaturated sites.

Strong metal-support interaction: The role of electronic and geometric factors in real Me/TiO2 catalysts

Abstract XPS, X-ray-induced AES (XAES), AES, SIMS, and ISS studies of metals (Pt, Rh) supported on TiO 2 powder catalysts combine to give new evidence in favor of electronic nature of SMSI. When reduced at high temperatures (HTR), the XPS spectra, of Me TiO 2 , corrected for extra-atomic relaxation, exhibit negative chemical shifts of core levels along with a gain in intensity of the density of states near the Fermi edge, indicating an increase of electron density on metal clusters. Tausters model of SMSI is further confirmed by the appearance of mixed RhTi + and RhTiO + clusters in SIMS spectra of Rh TiO 2 (HTR), which reflect direct interaction between metal atoms and Ti 3+ cations. The latter were detected by Ti L 3 M 23 V Auger peaks. The Rh + Ti + depth profile and the ISS Rh Ti ratio reveal some migration of TiO x entities onto metal surface, but no strong encapsulation of metallic particles is observed in real TiO 2 -supported catalysts reduced at temperatures as high as 500 °C. Thus, the observed decrease in the activities of Me TiO 2 in the C 2 H 6 hydrogenolysis and C 6 H 6 hydrogenation reactions seems to be accounted for by both geometric and electronic factors. The kinetics of 16 O 18 O homomolecular isotopic exchange measured for the first time on these catalysts is in accordance with the proposed SMSI model and explains its degradation during catalyst exposure to O 2 at low or elevated temperatures.

A new facility for inert transfer of reactive samples to XPS equipment

Abstract An express method for the transfer of reactive samples into UHV equipment is described. Samples are activated in a preconditioned form and handled in a protective gas. The operation of the system is illustrated by an XPS investigation of ammonium paratungstate reduction. After the transfer of pyrophoric tungsten powder no traces of reoxidation were detected in the W 4f spectrum.

Xps Study of Transition Metal Complexes in Zeolites

Abstract Transition metal complexes (TMC) fixed in Y zeolites by “surface assembling” [Ni, Co, Cu, Ru phthalocyanines (Pc)] or by exchanging Na + for [RuNO(NH 3 ) 4 OH] 2+ and [Rh(NH 3 ) 5 Cl] 2+ cations have been investigated by XPS. MePc were established to be located in supercages as isolated complexes which interact with zeolitic OH groups via meso N atoms of the porphyrin ring. The stability of both MePc and complex cations under various conditions of zeolites pretreatment was compared. MePc were found to be quite stable in inert and reducing atmosphere while Ru and Rh complexes decomposed causing the stabilization of metals in intermediate and zero-valence states. XPS combined with a catalytic study showed that zeolites with TMC are of great interest as promising metal-complex catalysts or precursors of zeolite supported catalysts with high dispersion of metals.

Mobility of oxygen and catalytic properties of rare earth oxides with respect to oxidation of hydrogen

1. Rare-earth oxides with high oxygen mobilities display maximum activity towards hydrogen oxidation. 2. It can be inferred from our experimental data that the most active rare-earth oxides should have good catalytic properties in other oxidation processes.

XPS studies of Ru inγ-Al2O3 supported catalysts

Two surface species of Ru established by XPS studies of Ru inγ-Al2O3 supported catalysts prepared via impregnation or adsorption from Ru(OH)Cl3 solution, are shown to have different reducibility and type of interaction with the support.AbstractИсследование методом РФЭС состояния Ru в нанесённых наγ-Al2O3 катализаторах, приготовленных пропиткой или адсорбцией из раствора Ru(OH)Cl3, показало, что имеются две поверхностные формы Ru, отличающиеся способностью к восстановлению и характером взаимодействия с носителем.

Oxidation of n-propanol over vanadium oxide catalysts

The kinetics of catalytic oxidation of n-propanol on V2O5 and V2O5 modified with BeO, MgO, CaO and SrO has been investigated. A high selectivity of the oxidation to propionaldehyde was observed. The activation energies of the reaction and of the exchange of oxygen in these catalysts with molecular oxygen and CO2 were found to change in parallel.AbstractИзучена кинетика гетерогенного каталитического окисления и-пропанола на V2O5 и V2O5 модифицированной BeO, CaO, MgO и SrO. Установлена высокая селективность окисления в пропионовый альдегид. Наблюдалось симбатное изменение энергии активации реакции и энергий активаций изотопного обмена кислорода исследуемых катализаторов с молекулярным кислородом и с кислородом и с кислородом двуокиси углерода.

Influence of a catalytic reaction on the surface composition and roughness factor of palladium-ruthenium alloys

Using X-ray photoelectron spectroscopy (XPS) and differential flow methods, the surface composition and surface area of Pd−Ru alloys have been examined before and after their use as catalysts. The increase in the catalytic activity of the alloys leads to the enrichment of their surface in ruthenium. It is concluded that the catalytic activity of these alloys is governed by the composition, structure and (to a lesser degree) the roughness of the surface.AbstractДля сплавов Pd−Ru до и после использования их в качестве катализаторов исследованы состав поверхности методом рентгеновской фотоэлектронной спектроскопии и удельная поверхность дифференциальным методом натекания. С ростом активности катализатора его поверхность сильно обогащалась рутением. Сделан вывод, что активность сплава определяется составом, структурой поверхности и в меньшей степени её шероховатостью.