A periodic DFT study of the activation of O-2 by Au nanoparticles on alpha-Fe2O3

Oxidation chemistry with supported Au nanoparticles as catalysts is an area of intense research. Even so there is still much discussion as to the nature of Au species generated on the complex surfaces of these catalysts and the types of oxygen species that are present. Recent experimental work has highlighted Au bi-layers with dimensions of 0.5 nm supported on iron oxide as a very efficient catalyst system for CO oxidation. This size scale implies clusters containing only 10 Au atoms, making the simulation of the nanoparticles, oxide surface and their interface amenable to perioidic density functional theory calculations. We present simulation results which demonstrate that the dissociation of O-2 is energetically favourable at the interface between nanoparticle and oxide, with both surface Fe cations and Au atoms taking part in the adsorption site. Here the barrier to dissociation of O2 is found to be lower than the energy required for molecular desorption which is not the case for isolated Au clusters. This reaction also produces oxidised Au atoms, as confirmed by Bader charge analysis. For isolated clusters we show that such oxidised Au species give rise to empty d-band states, whereas molecular adsorption of O-2 does not.