CO oxidation on phosphate-supported Au catalysts: Effect of support reducibility on surface reactions
2011
Li, Meijun | Wu, Zili | Overbury, S.H.
Previous work has shown that Au supported on FePO₄ can be stable and active for CO oxidation and that oxygen from the FePO₄ can participate in the CO oxidation. In this paper, we have used gas transient DRIFTS-QMS, Raman, temperature-programmed reduction and CO oxidation activity measurements to compare adsorption and oxidation of CO on two comparably loaded Au catalysts supported on both a reducible phosphate support, FePO₄, and a non-reducible support, LaPO₄. H₂-TPR confirms that the Au/FePO₄ catalyst is highly reducible and that the reduction is strongly promoted by the Au, while neither LaPO₄ nor Au/LaPO₄ are reducible up to 500°C. The nature of Au species was determined by CO adsorption. For Au/FePO₄, cationic Au is present after oxidative treatment, and metallic Au dominates after reductive treatment. The majority of the cationic Au observed on the FePO₄ support undergoes in situ reduction to metallic Au during rt CO adsorption. For Au/LaPO₄, no cationic Au is observed, but metallic Au is present after both oxidative and reductive treatment. In addition, metallic Au is accompanied by anionic Au, not seen on Au/FePO₄, which accumulates during CO exposure, even after an oxidative pretreatment. Unexpectedly, CO interacts rapidly with Au/LaPO₄ to evolve CO₂ and form both adsorbed CO₂ and “carbonate-like” species, even though the LaPO₄ is non-reducible and Raman fails to find evidence for loss of structural oxygen. H₂ coevolves with CO₂ during CO-TPR of Au/LaPO₄ (but not for Au/FePO₄) leading to the conclusion that surface hydroxyl is the source of oxygen during CO exposure to Au/LaPO₄. Anionic Au is associated with the vacancies remaining after reaction of hydroxyl with CO.
显示更多 [+] 显示较少 [-]