Vasko Idakiev

Low-temperature water-gas shift reaction over Au/CeO2 catalysts

A high and stable activity for gold/ceria catalyts has been established for the water-gas shift reaction. The relationship between gold loading and catalytic activity was studied over a wide temperature range. The influence of space velocity and H2O/CO ratio at different temperatures on the catalytic activity and stability was also investigated. The reduction/oxidation processes of ceria in the presence of gold was readily followed by TPR measurements. It was shown that ceria plays the role of an active support capable of producing oxygen. The high and stable activity of gold/ceria catalysts could arise from the high and stable gold dispersion present during the catalytic operation.

Low-temperature water-gas shift reaction on Auα-Fe2O3 catalyst

The water-gas shift reaction (WGSR) has been studied on Auα-Fe2O3 catalyst. The structure of the samples has been investigated by chemical and physical methods—TEM, X-ray, DTA, FTIR. A high dispersion degree of the gold particles and an increased concentration of the hydroxyl groups on Auα-Fe2O3 has been established in comparison to the pure α-Fe2O3. The results obtained can be explained on the basis of the associative mechanism of the WGSR. The essential aspects are the dissociative adsorption of water on ultrafine gold particles, followed by spillover of active hydroxyl groups onto adjacent sites of the ferric oxide. The formation and decomposition of intermediate species is accompanied by redox transfer Fe3+ Fe2+ in Fe3O4.

Influence of the microscopic properties of the support on the catalytic activity of Au/ZnO, Au/ZrO2, Au/Fe2O3, Au/Fe2O3–ZnO, Au/Fe2O3–ZrO2 catalysts for the WGS reaction

It has been established that the gold catalysts on well crystallized supports, Au/Fe2O3 and Au/ZrO2, display higher catalytic activity in the water gas shift (WGS) reaction in comparison with the samples on amorphous and not well crystallized supports — Au/ZnO, Au/ZrO2, Au/Fe2O3–ZnO and Au/Fe2O3–ZrO2. It could be concluded that the catalytic activity of the gold/metal oxide catalysts depends strongly not only on the dispersion of the gold particles but also on the state and the structure of the supports.

Au/α-Fe2O3 catalyst for water–gas shift reaction prepared by deposition–precipitation

A modified version of the preparation methods for the synthesis of highly-active Au/α-Fe2O3 catalysts for WGS reaction has been proposed. The results obtained show that gold dispersion is highly preserved and prevents cluster formation. On the other hand, a major part of gold remains on the surface, thus being accessible to catalysis. As a result of the preparation technique, it seems that the interaction between gold and support is weaker and, likely, more favourable for catalysis. This study demonstrates that a specific approach to preparation of catalysts of optimum structure and texture is crucial for high-catalytic activity.

Complete benzene oxidation over gold-vanadia catalysts supported on nanostructured mesoporous titania and zirconia

Abstract The new generation of gold-vanadia catalysts supported on mesoporous titania and zirconia for complete benzene oxidation were explored. The catalysts were characterized by X-ray, TEM, SEM, N2 adsorption analysis, TPR and ESR spectroscopy. The vanadia loading stabilized structure of the both mesoporous supports and this effect is stronger for zirconia comparing to titania. The presence of gold enhanced the V5+→V3+ reduction step and depending on the preparation method, differences in the reduction behavior were established. The catalytic activity of the catalysts also strongly depends on the preparation techniques. For the both series of the studied catalysts when the gold is loaded firstly the activity in complete benzene oxidation is higher than when the vanadia is deposited firstly (VAT>AVT and VAZ>AVZ). A strong synergistic effect between gold and vanadia supported on titania was observed and the catalysts on titania exhibit higher catalytic activity than the catalysts based on zirconia. Comparing the activity of the gold-vanadia/zirconia and gold/zirconia catalysts, it was established for the both catalysts high and equal activity in the reaction studied. The observed differences in the structural and catalytic properties of the both series of the studied catalysts were connected with the nature of the supports used.

Effect of copper oxide on the catalytic activity of iron-chromia catalyst for water gas shift reaction

It has been established that copper oxide promotes the catalytic activity of iron-chromia catalyst in the water gas shift reaction due to the formation of catalytically active aggregates. However, due to their gradual recrystallization and sintering into larger copper particles, the promoting effect sharply decreases.AbstractУстановлено, что окись меди промотирует каталитическую активность железохромного катализато ра окиси углерода, за счет образования катаитически активных агрегатов. Промотирующее действие меди быстро убывает, что связано с постепенной рекристаллиз ацией и спеканием каталитически активных агрегатв в более крупные кристаллы меди.

CO-free hydrogen production for fuel cell applications over Au/CeO2 catalysts: FTIR insight into the role of dopant.

The impact of ceria doping by Zn (atomic ratio Zn/(Zn + Ce) = 0.05) on the structural and catalytic properties of Au/CeO(2) catalyst was studied. The ceria modification influenced the catalytic activity toward purification of hydrogen via water-gas shift (WGS) and preferential CO oxidation (PROX) reactions in a different way: it diminished the WGS activity and improved the PROX performance. A characterization by FTIR spectroscopy was conducted to explain differences in the catalytic performance. The nature of gold active species after different pretreatments, under different atmospheres (H(2), D(2)), and after admission of CO and its subsequent interaction with (18)O(2) was investigated. Evidence has been found of the dissociation of hydrogen at room temperature on gold, producing on the oxidized sample a broad absorption assigned to Au-OH vibrations, whereas on the reduced one, bands at 3200 and 1800 cm(-1) ascribed, respectively, to Au-OH and Au-H species have been detected. For the first time, the formation of Au-hydride on supported heterogeneous catalysts was proposed. These features were stronger on the Au/CeO(2) sample than on the Au/Zn-CeO(2) sample. The availability of highly dispersed gold clusters in contact with oxygen vacancies on the ceria surface could contribute to higher WGS activity, whereas the steps of small gold particles are the active sites for both CO and oxygen activation during the PROX reaction.

Complete oxidation of benzene over Au−V2O5/TiO2 and Au−V2O5/ZrO2 Catalysts

A gold promotional effect is reported for the complete oxidation of benzene using Au/V2O5 supported on titania or zirconia catalysts.

Viability of Au/CeO2–ZnO/Al2O3 Catalysts for Pure Hydrogen Production by the Water–Gas Shift Reaction

The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the water–gas shift reaction. Herein, a series of gold catalysts supported on ZnO‐promoted CeO2–Al2O3 are presented as interesting systems for the purification of H2 streams through the water–gas shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn‐containing solids. High activity and good stability and resistance towards start‐up–shut‐down situations was found, which makes these catalysts a promising alternative for CO clean‐up applications.

Impact of Ce–Fe synergism on the catalytic behaviour of Au/CeO2–FeOx/Al2O3 for pure H2 production

In this work the development of a series of gold catalysts, essentially based on γ-alumina promoted with a small superficial fraction of Ce–Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce–Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce–Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up.