Quantum-Chemical Calculations on the Mechanism of the Water-Gas Shift Reaction on Nanosized Gold Cluster

We have studied the mechanism of the water gas shift reaction (WGS, CO + H2O -> CO2 + H-2) catalyzed by nanosized gold particles by using density functional theory calculations. The molecular structures and adsorbate/substrate interaction energies of H2O/Au-38, CO/Au-38, HO/Au-38, and H/Au-38 configurations were predicted. Several adsorption sites on the Au-38 nanoparticle were considered in this study and characterized as top, bridge, hollow, and hcp sites. A potential energy surface for WGS reaction on the Au-38 nanoparticle has been constructed using the nudged elastic band method. It was found that water dissociation (H2O -> H + OH) is the rate-limiting step, with an energy barrier of 31.41 kcal/mol. The overall reaction CO + H2O + Au-38 -> CO2 + H-2 + Au-38 is exothermic by 16.18 kcal/mol. To gain insights into the high catalytic activity of the gold nanoparticles, the nature of the interaction between adsorbate and substrate is also analyzed by the detailed electronic local density of states.