(502b) Importance of Au/Oxide Interface on the Water-Gas Shift Reaction: A Computational Study

Water gas shift (WGS) reaction is a very important industrial reaction, especially in the manufacture of hydrogen, ammonia, methanol and hydrocarbons. Oxide supported Au catalyst has gained great attraction on WGS reactions, especially for its catalytic activity at low temperatures, since the discovery of its unique chemical properties. In this study, we did density functional theory (DFT) calculations at generalized gradient approximation level with exchange-correlation functional in form of PW91 as well as at hybrid level in form of HSE06. A supported gold nano-wire on an extend MgO(100) slab model was used to explore the reaction mechanism of WGS at Au/oxide interface, which was believed to be the active site by several previous experimental studies. Compared to the previous theoretical study on Au(111) itself, the biggest difference of the reaction at Au/MgO interface is that the water dissociation barrier is dramatically decreased from > 2 eV over Au(111) to no barrier at Au/MgO interface. Among the previous proposed redox, carboxyl and formate mechanisms, the carboxyl mechanism is the most plausible one, with the formation of COOH having the highest barrier at ~0.8 eV. Based on these DFT calculated barriers, a two sites micro-kinetic model was built at Au/MgO interface. Kinetic control analysis shows that COOH formation to be rate-determing step. The competitive adsorption between CO and H at the interface also strongly influence the reaction kinetics. In order to improve the performance of Au/MgO, two suggestion can be made based on currently calculations: 1) lower the barrier of rate-determing step, formation of COOH; 2) enhance the binding of water or hydroxyl group to reduce the poison by CO and H.