Theoretical Study of the CO Oxidation Mediated by Au3~+, Au3, and Au3~- : Mechanism and Charge State Effect of Gold on Its Catalytic Activity

摘要

By carrying out density functional theory calculations, we studied the CO oxidation promoted by cationic, neutral, and anionic Au trimers, which represent the prototypes of Au-cluster-based catalysts with different charge states. The reaction is explored along three possible pathways: one involves the reaction of the initial complexes between Au trimers and O2 with CO; another is related to O2 interacting with the complexes between Au trimers and CO; and the third refers to a self-promoting mechanism; that is, the second CO oxidation is promoted by a preadsorbed CO molecule. The theoretical results show that all three species may promote the reaction, as indicated by calculated low energy barriers and high exofhermicities, supporting the fact that cationic, neutral, and anionic Au species were all observed to present catalytic activity toward CO oxidation. Along the reaction coordinates for all of the reactions, Au-carbonate species are not found to be the necessary intermediates, although they are calculated to be energetically very stable. In contrast, by performing atom-centered density matrix propagation molecular dynamics simulations, the formation of such highly stable species is attributed to the effective collision between Au-oxides and CO2 with the carbon atom of CO2 directly attacking the 0 atom in the oxides. The present results enrich our understanding of the catalytic oxidation of CO by Au-cluster-based catalysts.