Journal
CATALYSIS SCIENCE & TECHNOLOGY
Volume 5, Issue 2, Pages 925-941Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4cy01030b
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Funding
- Alexander von Humboldt-Foundation
- Ministry of Science, Research and the Arts of Baden-Wurttemberg
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Aiming at further insight into the mechanism of the preferential CO oxidation (PROX) and the (reverse) water gas shift (R)WGS reaction over Au/CeO2 catalysts, we investigated the removal of stable, active surface oxygen from a Au/CeO2-supported catalyst by H-2 by quantitative temporal analysis of products (TAP) measurements over a wide range of temperatures (30-300 degrees C) and compared it with the removal of active oxygen by reaction with CO and a CO-H-2 mixture. It is demonstrated that a surface-oxidized Au/CeO2 catalyst can be reduced by H-2 pulses only at temperatures higher than 80 degrees C, whereas significant reduction of the catalyst surface by CO or CO/H-2 pulses is possible already at 30 degrees C. Even at 300 degrees C, removal of surface oxygen by H-2 or CO pulses is possible only in the presence of Au nanoparticles, underlining that these processes are Au assisted. At all temperatures investigated, the amount of H-2 necessary to remove the available active surface oxygen is much higher than that of CO. Hence, over the whole range of temperatures the efficiency of H-2 to surface reduce a Au/CeO2 catalyst is much lower than that of CO or of a CO-H-2 mixture. On the other hand, it is significantly higher than that for active oxygen deposition from CO2, indicating that under steady-state reaction conditions during the RWGS reaction surface lattice oxygen vacancies are present on the surface. Furthermore, the influence of adsorbates resulting from H-2, such as hydroxyl groups or water, on the oxygen storage capacity (OSC) of Au/CeO2 catalysts and on the active oxygen deposition from CO2 was elucidated. Implications of these results for the mechanistic understanding of the PROX and the (R) WGS reaction in H-2-rich gases are discussed.
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