Tatyana Tabakova

FTIR study of low-temperature water-gas shift reaction on gold/ceria catalyst

Chemisorption and reactivity of the molecules involved in the water-gas shift (WGS) reaction on gold/ceria catalyst have been studied at 90 and 300 K by FTIR spectroscopy. Forward and reverse WGS reaction at 300 K and up to 573 K have been investigated, too. The FTIR results show that gold causes a strong modification of the surface properties of the support. The nanosized metallic gold particles in close contact with defective ceria play an essential role for the genesis of high catalytic activity in WGS reaction at low temperature and appear to be of crucial importance in explaining the remarkably high stability of this catalytic system. An electronic interaction between small gold metallic nanoparticles and ceria has been evidenced.

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.

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.

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.

Titanium oxide nanotubes as supports of Au or Pd nano-sized catalysts for total oxidation of VOCs

Abstract Titanium oxide nanotubes (TNTs) have been synthesized via laboratory-made TiO2 A and commercial TiO2 P25. 1.5wt% gold or palladium were deposited on TNTA and TNTP25 supports and the catalytic activity was evaluated in propene, methyl ethyl ketone (MEK) and toluene total oxidation. The catalytic properties of supported TNT were correlated with the structural peculiarity and the nature of the TNT, but also with the nature of the noble metal and the kind of the VOC.

Structure–reactivity relationship in Co3O4 promoted Au/CeO2 catalysts for the CH3OH oxidation reaction revealed by in situ FTIR and operando EXAFS studies

A strong influence of the amount of the Co3O4 promoter on the catalytic performance in methanol oxidation of different gold catalysts supported on ceria was observed. The activity followed the order: Au/10 wt% Co3O4-doped CeO2 > Au/5 wt% Co3O4-doped CeO2 > Au/15 wt% Co3O4-doped CeO2 > Au/CeO2 ≫ Au/Co3O4. FTIR measurements of adsorbed CO indicate that oxidized gold sites are initially present on the activated samples and that such species are involved in the methanol reaction. Methanol oxidation performed under static conditions gave rise at 75 °C to mainly formate species on Au/CeO2 and to a large variety of different carbonate species on Au/10 wt% Co3O4-doped CeO2. FTIR and EXAFS analyses revealed that the active sites present on the best performing Au/CeO2 catalyst added with 10 wt% Co3O4 are oxidized gold species, close to Co sites, at the interface with the support, which are reduced under reaction conditions. These species are able to activate and to react with oxygen giving rise to formate and carbonate species.

Catalytic abatement of CO and volatile organic compounds in waste gases by gold catalysts supported on ceria-modified mesoporous titania and zirconia

Mesoporous oxides TiO2 and ZrO2, synthesized by surfactant templating via a neutral C13(EO)6–Zr(OC3H7)4 assembly pathway, and ceria-modified TiO2 and ZrO2, prepared by a deposition–precipitation (DP) method, featuring high surface areas and uniform pore size distributions were used as supports for gold catalysts. The supported gold catalysts were assessed for the catalytic abatement of air pollutants, i.e., CO, CH3OH, and (CH3)2O. The gold was supported on the mesoporous oxides by a DP method. The supports and catalysts were characterized by powder X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption–desorption analysis, and temperature-programmed reduction technique. A high degree of synergistic interaction between ceria and mesoporous ZrO2 and TiO2 as well as a positive modification of the structural and catalytic properties by ceria was observed. The ceria additive interacts with the mesoporous oxides and induces a strong effect on the reducibility of the supports. The catalytic behavior of the catalysts was discussed to determine the role of the ceria modifying additive and possible interaction between the gold nanoparticles and ceria-mesoporous oxide supports. The gold catalysts supported on ceria-modified mesoporous ZrO2 displayed superior catalytic activity (∼100% conversion of CO at 10 °C and CH3OH at 60 °C). The high catalytic activity can be attributed to the ability of the support to assist oxygen vacancies formation. The studies indicate that the ceria-modified mesoporous oxide supports have potential as supports for gold-based catalysts.

Gold catalysts on ceria doped with MeOx (Me = Fe, Mn, Co and Sn) for complete benzene oxidation: effect of composition and structure of the mixed supports

Gold catalysts supported on ceria doped with different metal oxides (Fe, Mn, Co and Sn) were synthesized using two techniques: CP and mechanochemical activation. The catalytic activity in complete benzene oxidation (CBO) was studied. The samples were characterized by means of XRD and high resolution transmission electron microscopy, and non-significant differences in the average size and the distribution of gold particles were observed. This means that the main reason for the different catalytic behavior in CBO has to be searched in the composition and structure of the supports. In spite of the higher hydrogen consumption (e.g., higher oxygen mobility) estimated by means of TPR, the gold catalysts on ceria doped with transition metal oxides generally are less active than gold/ceria catalyst. This observation could be explained taking into consideration that the key factor for the high oxidation activity is not the oxygen supplying but the activation of the very stable benzene molecule. The higher catalytic activity in comparison with that of the gold/ceria catalyst was observed only using a mixed ceria–CoOx support mechanochemically prepared. Very high and stable catalytic activity in CBO was obtained over this sample.

Gold catalysts supported on mixed oxides for hydrogen production

The support of this new catalytic system concerns ceria-modified mesoporous titania (CeMTi). Mesoporous TiO 2 (MTiO 2 ) with high surface area and uniform pore size distribution was synthesized using surfactant templating method through a neutral [C 13 (EO) 6 -Ti(OC 3 H 7 ) 4 ] assembly pathway. Ceria modifying additive was deposited on suspended in water MTiO 2 by means of precipitation with Na 2 CO 3 . Gold-based catalysts with different gold loading were synthesized by deposition-precipitation of gold hydroxide on mixed metal oxide support. The support and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and N 2 adsorption analysis. The catalytic behavior of the gold-based catalysts was evaluated in water-gas shift reaction (WGSR) at a wide temperature range (140-300 °C). The influence of gold content and particle size on the catalytic performance was investigated. The CO conversion of the new catalysts was compared with that related to the gold catalysts supported on simple oxides CeO 2 and mesoporous TiO 2 as well as and to reference Au/TiO 2 type A (World Gold Council).