Adsorption and dissociation of O2 on gold surfaces:: Effect of steps and strain

The activation of dioxygen via dissociation on strained and stepped gold surfaces has been studied using periodic self-consistent (GGA-PW91) density functional theory (DFT) calculations. Although we find that molecular oxygen does not adsorb on Au(111), it does bind, albeit weakly, to an Au(111) surface stretched by 10% as well as to Au(211) surfaces both stretched and unstretched. The most stable molecular states on all three surfaces have the top-bridge-top configuration and carry about half of the magnetic moment of gas-phase O-2. On 10%-stretched Au(111), unstretched Au(211), and 10%-stretched Au(211), the binding energies of O-2 are -0.08, -0.15, and -0.26 eV, respectively, and the activation energies of O-2 dissociation are 1.37, 1.12, and 0.63 eV. Both steps and tensile strain enhance the adsorption of atomic and molecular oxygen. A comparison between unstretched and stretched Au(211) indicates that the enhancing effect of tensile strain is less pronounced on the step edge than on the flat terrace. The magnitude of the dissociation barriers, combined with the fact that the transition states lie above the gas-phase zero on all three surfaces, suggests that O-2 dissociation remains an activated process on gold. Although additional factors may be involved in O-2 activation at low temperatures on oxide-supported Au catalysts, the present work shows that steps and tensile strain substantially facilitate O-2 activation on Au surfaces.