Exploring the Effects of a Doping Silver Atom on Anionic Gold Clusters' Reactivity with O2.

Abstract

Reactivities of AgAun-1- (n = 3-10) with O2 at a low temperature were studied using an instrument combining a magnetron sputter cluster source, a microflow reactor, and a time-of-flight mass spectrometer. Their reaction products as well as size-dependent kinetic rates were nearly identical to those of corresponding Aun- (n = 3-10). Previous experiments showed that the Ag atom in AgAun-1- (n = 3-10) was fully or partially enclosed by the gold atoms. We studied the adsorption of O2 on these reported structures using the B3LYP theory with relatively large basis sets. The theoretical results indicate that the adsorption sites as well as the adsorption energies of O2 on AgAun-1- (n = 3-10) are nearly identical to those on the corresponding Aun- (n = 3-10). The O2 adsorption on a series of proposed isomers of AgAun-1- (denoted as Aun-1Ag-), in which the silver atom was on the protruding site, was explored using the same theoretical methods. The O2 tends to bond with the protruding Ag atoms, and the binding energies are apparently higher than those on the corresponding Aun- and AgAun-1-. The adsorption and activation of O2 on Aun-, AgAun-1-, and Aun-1Ag- were correlated with their global electron detachment energies (VDEs) as well as the element types of the adsorption sites. Generally, low VDE values and silver sites facilitate the O2 adsorption, and these two factors separately dominate in various cluster species. The revealed effects of a doping silver atom in small gold clusters are helpful to understand the role of the residual silver components in many nano gold catalysts.