Low temperature water-gas shift: Examining the efficiency of Au as a promoter for ceria-based catalysts prepared by CVD of a Au precursor

Gold and platinum promoted catalysts were compared in a suitable reaction temperature range after first ensuring that metal-oxide interactions were overcome (ca. 5% metal loading). Approximately 20 times the amount of 5% Au/ceria catalyst was required to achieve a lightoff curve similar to that of a 5% Pt/ceria in the temperature range 200-300 °C, and 5% Pt/ceria also exhibited higher steady-state activity (about double that of Au) at 175 °C. This result suggests that, in addition to the role the metal plays in facilitating the formation of the active site bridging OH groups, it also influences the intrinsic rate of the WGS reaction. Transient formate decomposition experiments carried out at 140 °C indicated that the rate of formate decomposition was approximately 20 times higher for 2.5% Pt/ceria than that of 2.5% Au/ceria, suggesting that the metal (in addition to the promoting effect of H2O previously reported) plays a role in facilitating the decomposition of surface formate intermediates, the proposed rate limiting step of the reaction mechanism.