Reaction Mechanisms for the CO Oxidation on Au/CeO2 Catalysts: Activity of Substitutional Au3+/Au+ Cations and Deactivation of Supported Au+ Adatoms

作者：Matteo Farnesi Camellone, Stefano Fabris · 发表于：Journal of the American Chemical Society · 年份：2009 · DOI：10.1021/ja902109k · 被引用次数：330 · 研究领域：Catalytic Processes in Materials Science、Catalysis and Oxidation Reactions、Catalysis and Hydrodesulfurization Studies

Density functional theory calculations that account for the on-site Coulomb interaction via a Hubbard term (DFT+U) reveal the mechanisms for the oxidation of CO catalyzed by isolated Au atoms as well as small clusters in Au/CeO(2) catalysts. Ceria (111) surfaces containing positively charged Au ions, either as supported Au(+) adatoms or as substitutional Au(3+) ions, are shown to activate molecular CO and to catalyze its oxidation to CO(2). In the case of supported single Au(+) adatoms, the limiting rate for the CO oxidation is determined by the adsorbate spillover from the adatom to the oxide support. The reaction then proceeds with the CO oxidation via lattice oxygen and O vacancy formation. These vacancies are shown to readily attract the supported Au(+) adatoms and to turn them into negatively charged Au(delta-) adspecies that deactivate the catalyst, preventing further CO adsorption. Au(3+) ions dispersed into the ceria lattice as substitutional point defects can instead sustain a full catalytic cycle consisting of three individual steps maintaining their activity along the reaction process: Au cations in Au(x)Ce(1-x)O(2) systems promote multiple oxidations of CO without any activation energy via formation of surface O vacancies. Molecular oxygen adsorbs at these vacancies and forms O adspecies that then catalyze the oxidation of molecular CO, closing the catalytic cycle and recovering the stoichiometric Au(x)Ce(1-x)O(2) system. The interplay between the reversible Ce(4+...