New insight into mechanisms in water-gas-shift reaction on Au/CeO2(111): A density functional theory and kinetic study

Abstract

Using density functional theory (DFT) and kinetic analyses, a new carboxyl mechanism for the water-gas-shift reaction (WGSR) on Au/CeO₂(111) is proposed. Many elementary steps in the WGSR are studied using an Au cluster supported on CeO₂(111). It is found that (i) water can readily dissociate at the interface between Au and CeO₂; (ii) CO₂ can be produced via two steps: adsorbed CO on the Au cluster reacts with active OH on ceria to form the carboxyl (COOH) species and then COOH reacts with OH to release CO₂; and (iii) two adsorbed H atoms recombine to form molecular H₂ on the Au cluster. Our kinetic analyses show that the turnover frequency of the carboxyl mechanism is consistent with the experimental one while the rates of redox and formate mechanisms are much slower than that of carboxyl mechanism. It is suggested that the carboxyl pathway is likely to be responsible for WGSR on Au/CeO₂.