Gas-Phase Reactivity of Gold Oxide Cluster Cations with CO

Abstract

Gold oxide cluster cations, containing one to four gold atoms and between one and five oxygen atoms, were investigated employing guided-ion-beam mass spectrometry to gain insight into their reactivity with CO. Clusters with one atomically bound oxygen atom (AuO+, Au2O+, and Au3O+) were found to be reactive and selective toward oxidation of one CO molecule facilitated by adsorption of a second CO. Furthermore, the mono-oxide clusters with an odd number of gold atoms (AuO+ and Au3O+) were determined to be more reactive than Au2O+. Species with higher oxygen content favored adsorption of one CO molecule onto the cluster accompanied by the loss of either one or two O2 molecules, indicating that binding of O2 molecules to positively charged gold clusters does not prevent the subsequent chemisorption of CO. Clusters with two or more gold atoms exhibited products corresponding to loss of AuO2 when reacted with CO. Positively charged gas-phase gold clusters, therefore, may be broken apart by the exothermic adsorption of CO. Product cluster ions resulting from these O2 and AuO2 loss processes appear to show further reactivity for both the oxidation of CO and the adsorption of additional CO molecules. These findings provide insight into the role of positively charged centers in gold based nanocatalysis.