Reactive removal of surface oxygen by H2, CO and CO/H2 on a Au/CeO2 catalyst and its relevance to the preferential CO oxidation (PROX) and reverse water gas shift (RWGS) reaction. Issue 2 (22nd October 2014)

• Record Type: Journal Article
• Authors: Wang, L. C.; Widmann, D.; Behm, R. J.
• Is Part Of: Catalysis science & technology. Volume 5:Issue 2(2015:Feb.)
• Page Start: 925
• Page End: 941
• Publication Date: 2014-10-22
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c4cy01030b
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : CO and H2 compete for the same active surface (lattice) oxygen species, but with a much lower reduction efficiency of H2 compared to CO and CO–H2 mixtures, during removal of active oxygen from a Au/CeO2 catalyst by H2, CO or CO/H2 at temperatures between 30 and 300 °C. Abstract : 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 H2 by quantitative temporal analysis of products (TAP) measurements over a wide range of temperatures (30–300 °C) and compared it with the removal of active oxygen by reaction with CO and a CO–H2 mixture. It is demonstrated that a surface-oxidized Au/CeO2 catalyst can be reduced by H2 pulses only at temperatures higher than 80 °C, whereas significant reduction of the catalyst surface by CO or CO/H2 pulses is possible already at 30 °C. Even at 300 °C, removal of surface oxygen by H2 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 H2 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 H2 to surface reduce a Au/CeO2 catalyst is much lower than that of CO or of a CO–H2 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 H2, 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 H2 -rich gases are discussed.