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

The oxidation of CO by Au/Fe(2)O(3) and Au/ZnO catalysts is compared in the very early stages of the reaction using a temporal analysis of products (TAP) reactor. For Au/Fe(2)O(3) pre-dosing the catalyst with (18)O labelled water gives an unexpected evolution order for the labelled CO(2) product with the C(18)O(2) 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/Fe(2)O(3) 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.

A periodic DFT study of the activation of O2 by Au nanoparticles on α-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 O2 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 O2 does not.

Theory and simulation in heterogeneous gold catalysis.

This critical review covers the application of quantum chemistry to the burgeoning area of the heterogeneous oxidation by Au. We focus on the most established reaction, the oxidation of CO at low temperature. The review begins with an overview of the methods available comparing the treatment of the electron-electron interaction and relativistic effects. The structure of Au particles and their interaction with oxide reviews is then discussed in detail. Calculations of the adsorption and reaction of CO and O2 are then considered and results from isolated and supported Au clusters compared (155 references).