Participation of interfacial hydroxyl groups in the water-gas shift reaction over Au/MgO catalysts

Abstract

Au/MgO and Au/Mg(OH)₂ catalysts were prepared and used as model systems to study the participation of the Au–support interface in the water-gas shift reaction (WGS). Au/MgO and Au/Mg(OH)₂ showed similar WGS kinetics, consistent with a similar WGS reaction mechanism. However, Au/MgO had a lower apparent reaction order with respect to H₂O and was identified as having a higher specific WGS rate compared with Au/Mg(OH)₂ at the same average Au particle size. The focus of the work is on Au/MgO, where we observed a correlation between the hydroxyl group coverage and WGS rate. The measured kinetic isotope effect, DFT calculations, and operando FTIR for that catalyst are all consistent with surface carboxyl formation as the rate-determining step. Comparisons of hydroxyl group coverage with and without Au suggest that the formation of OH groups is strongly influenced by the presence of Au and likely to be highest at the Au–MgO interface, as supported by theoretical calculations. Temperature programmed reaction shows that Au is necessary to catalyze reaction of the surface OH groups with CO. This work confirms the importance of the metal support interface in WGS catalysis and suggests that the unique chemistry at the interface offers both an explanation of catalyst behaviour and a new opportunity to design materials with improved function for additional catalytic applications.