CO Oxidation on the Au15Cu15 Cluster and the Role of Vacancies in the MgO(100) Support

A domprehensive theoretical study of a Au15Cu15 cluster on MgO(100) supports and its catalytic activity for CO oxidation has been performed based on the density functional theory and microkinetic modeling. Molecular adsorption and different reaction paths based on the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms have been explored by tuning the location of vacancies in MgO(100). The charge states of the Au15Cu15 cluster are negative on all supports, defect-free, O-vacancy (F-center), and Mg-vacancy (V-center), and the effect is significantly amplified on the F-center. In each case, the O-2 molecule can be effectively activated upon adsorption and dissociated to 2 x O atoms easily, and the reaction modeling takes into account also the reaction paths with adsorbed O atoms. Overall, CO oxidation has lower reaction barriers on the cluster on the F-center. The microkinetic modeling analysis reveals that CO oxidation is very sensitive to the CO partial pressure, as the relatively strong CO binding leads readily to CO poisoning of the cluster surface sites and hinders CO2 formation. For low CO partial pressures, the catalytic reaction takes place already at 150 K for the cluster on the F-center. The CO, production rates are much lower for the defect-free and V-center supports which display similar increased activity at elevated temperatures. In all cases, the right combination of CO and O-2 partial pressures is instrumental for CO2 production.