Reaction pathway analysis for CO oxidation over anionic gold hexamers using DFT

Abstract

The reaction pathways for CO oxidation over anionic gold hexamer (Au6−) as a model catalyst were studied using unrestricted density functional theory (UDFT). The reaction mechanisms for two possible initial structures, in which either CO or O2 was adsorbed on the apex site while the other was on the nearest lateral site, were analyzed. The reaction proceeds through a typical Langmuir–Hinshelwood mechanism taking place in two steps for both initial structures. First, CO reacts with the molecular O2 leading to the first CO2 molecule and Au–O complex through the formation of a four-centered intermediate structure (CO–OO). This is followed by the elimination of the remaining O on the cluster by another CO. It was found that the energy barriers for the formation of the intermediate and its decomposition into CO2 and Au–O complex were much lower when O2 was bonded to the apex site. The second step, on the other hand, was found to be identical for both initial structures.