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

Reactivities of AgAu^- (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 Au^- (n = 3-10). Previous experiments showed that the Ag atom in AgAu^- (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 AgAu^- (n = 3-10) are nearly identical to those on the corresponding Au^- (n = 3-10). The O₂ adsorption on a series of proposed isomers of AgAu^- (denoted as AuAg^-), 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 Au^- and AgAu^-. The adsorption and activation of O₂ on Au^-, AgAu^-, and AuAg^- 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.