CO Self-Promoting Oxidation on Nanosized Gold Clusters: Triangular Au₃ Active Site and CO Induced O–O Scission

Abstract

We have systematically studied the CO oxidation on various nanosized gold clusters with sizes ranging from 0.3 to 0.8 nm on the basis of density functional theory (DFT) calculations. A hitherto unreported trimolecular Langmuir-Hinshelwood (LH) mechanism is proposed, which offers new insights into the fundamental mechanism for CO oxidation on nanosized gold clusters. Specifically, we find that the coadsorbed CO molecule at a unique triangular Au(3) active site can act as a promoter for the scission of an O-O bond, leading to the spontaneous formation (due to extremely low energy barrier) of two CO(2) molecules as product. The key step to the O-O bond scission in the OCOO* intermediate is significantly accelerated due to the electrophilic attack of the coadsorbed neighboring CO molecule on the triangular Au(3) site. This new mechanism is called CO self-promoting oxidation, which can be visualized in real time from the trajectory of a Born-Oppenheimer molecular dynamics (BOMD) simulation. We also find that such CO self-promoting oxidation is quite universal, as long as the triangular Au(3) reaction site is available. This is demonstrated in two prototype metal oxide supported gold nanostructure systems: namely, Au(n)/MgO and bilayer-Au/TiO(2). The coadsorbed CO can not only serve as a promoter for its own oxidation but also promote other oxidation reactions such as styrene oxidation through expediting O-O scission on gold nanostructures.