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The stability of Au supported catalysts for the water–gas shift reaction was studied. Two types of continuous flow experiments were performed, i.e. temperature-programmed and long-term isothermal stability test. The highest initial rate was obtained for catalysts used without any calcination or other high-temperature treatment. The continuous flow experiments showed that all Au/Fe2O3 catalysts deactivated under water–gas shift conditions. The deactivation trend occurred independently on the Au loading, the method of preparation, calcination or high-temperature treatment. The various causes on the deactivation, i.e. the formation of carbon-containing species, the change of Au particles or changes of the support were investigated in terms of DRIFTS coupled with MS, TGA, TEM, N2 physisorption, ICP, and XRD. Even though stable carbonate and carbonyl surface species were found on the spent catalysts, the quantity of these species indicated that they are not the main cause of the deactivation. Furthermore, the agglomeration of the Au particles was not severe and was not observed for all Au catalysts. The deactivation of Au/Fe2O3 was mainly caused by the change of the support. A significant reduction of the surface area of the support is taking place during the water–gas shift reaction as a function of time on stream. This decrease of the surface area can almost solely explain the decrease on the catalytic activity. [ABSTRACT FROM AUTHOR]

The physico-chemical properties of ceria (CeO2) and rare earth modified ceria (with La, Pr, Sm, Y) catalysts are studied and correlated with the soot oxidation activity with using O2 and O2 + NO. CeO2 modified with La and Pr shows superior soot oxidation activity with O2 compared with the unmodified catalyst. The improved soot oxidation activity of rare earth doped CeO2 catalysts can be correlated to the increased meso/micro pore volume and the stabilisation of the external surface area. On the other hand, unreducible ions decrease the intrinsic soot oxidation activity of rare earth modified ceria with both O2 and NO + O2 due to the decreased amount of redox surface sites. The catalyst bulk oxygen storage capacity is not a critical parameter in determining the soot oxidation activity. The modification with Pr shows the best soot oxidation with both O2 and O2 + NO compared with all other catalysts. [ABSTRACT FROM AUTHOR]

Various Fe-BEA catalysts have been synthesized by liquid ion-exchange, varying the iron precursor (nitrate, sulfate or chloride), the iron content (0.2–1.5 wt% Fe), and the conditions of activation, i.e. atmosphere (air or inert) and heating rate (5 or 20 K min-1). The catalysts were tested in direct N2O decomposition in the temperature range of 625–825 K. An optimal iron loading of 0.8 wt% Fe was found, with no significant influence of the used Fe-precursor. Activation of the ion-exchanged catalysts in inert gas yields significantly better performance than activation in air. NO adsorption combined with infrared analysis was used to characterize the various Fe2+ species present in the differently prepared Fe-BEA zeolites. A correlation exists between the absorption intensity of NO at 1874 cm-1 and the activity of the catalysts in N2O decomposition. This relationship, which can be used as a reliable and fast assessment of catalyst performance, suggests an important role of ferrous ions in the activity of these catalysts. Based on these results and previous mechanistic studies using transient techniques, the NO absorption band at 1874 cm-1 is tentatively assigned to oligonuclear oxocations in the zeolite channels, with general formula FexOy. [ABSTRACT FROM AUTHOR]

The decomposition of N2O is strongly promoted by NO over steam-activated FeZSM-5. The promoting effect of NO is catalytic, and in addition to NO2, О2 is formed much more extensively at lower temperatures than in the absence of NO. The promotion effect only requires low NO concentrations in the feed, with no significant improvements at molar NO/N2O feed ratios higher than 0.25. No inhibition by NO was identified even at a molar NO/N2O feed ratio of 10, suggesting different sites for NO adsorption and oxygen deposition by N2O. The latter sites seem to be remote from each other. Transient experiments using in situ FT-IR/MS and Multitrack over FeZSM-5 further elucidate the mechanism of NO promotion. The release of oxygen from the catalyst surface during direct N2O decomposition is a rate-determining step due to the slow oxygen recombination, which is favored by high reaction temperatures. NO addition promotes this oxygen desorption, acting as an oxygen transfer agent, probably via NO2 species. Adsorbed NO may facilitate the migration of atomic oxygen to enhance their recombination. Less than 0.9% of Fe seems to participate in this promotion. A model is proposed to explain the phenomena observed in NO-assisted N2O decomposition, including NO2 decomposition. [ABSTRACT FROM AUTHOR]

We report on a 197Au Mössbauer study of several types of supported gold catalysts. Differences in particle size show up in the Mössbauer spectra by a change in the relative weight of the spectral contribution of the surface atoms. The presence of ionic gold in active gold catalysts is not observed. The spectra can be interpreted in terms of bulk-like contributions from the inner-core atoms plus contributions from the outermost atoms at the surface of the particles. [ABSTRACT FROM AUTHOR]

A series of Ni on alumina washcoated monoliths has been prepared and characterized. The selective liquid-phase hydrogenation of benzaldehyde to benzyl alcohol in a Berty reactor has been used as a test reaction. [ABSTRACT FROM AUTHOR]