CO bond cleavage on supported nano-gold during low temperature oxidation

The oxidation of CO by Au/Fe2O3 and Au/ZnO catalysts is compared in the very early stages of the reaction using a temporal analysis of products (TAP) reactor. For Au/Fe2O3 pre-dosing the catalyst with O-18 labelled water gives an unexpected evolution order for the labelled CO2 product with the (CO2)-O-18 emerging first, whereas no temporal differentiation is found for Au/ZnO. High pressure XPS experiments are then used to show that CO bond cleavage does occur for model catalysts consisting of Au particles deposited on iron oxide films but not when deposited on ZnO films. DFT calculations, show that this observation requires carbon monoxide to dissociate in such a way that cleavage of the CO bond occurs along with dynamically co-adsorbed oxygen so that the overall process of Au oxidation and CO dissociation is energetically favourable. Our results show that for Au/Fe2O3 there is a pathway for CO oxidation that involves atomic C and O surface species which operates along side the bicarbonate mechanism that is widely discussed in the literature. However, this minor pathway is absent for Au/ZnO.