Low Temperature Water–Gas Shift Reaction: Interactions of Steam and CO with Ceria Treated with Different Oxidizing and Reducing Environments

Abstract

In a recent review article, it was suggested that a redox mechanism best describes observations regarding the WGS reaction for metal promoted ceria systems, as well as how molecules such as CO, CO₂, H₂O, and H₂ interact with the ceria surface. In this contribution, the pretreated surface of Pt/ceria was subjected to steaming or H₂ treatment at 250 °C followed by CO adsorption after six different pre-treatment sequences were performed. Subjecting a H₂-treated surface directly to CO, or followed by steaming, led to the highest concentration of surface formates by reaction of CO with Ce³⁺ defect-associated Type II bridging OH groups. The Type II OH groups were also generated by CO treatment followed by steaming. Using CO as a probe led to a significant coverage of formate species, though less than the previous cases (CO added to a H₂ treated surface or a surface treated with H₂, then H₂O). Surprisingly, even subjecting an oxidized surface (pre-reduced and subjected to O₂ at 400 °C) to steam still produced a significant density of Type II OH groups, as evidenced by the formates produced upon exposure to CO. The formates were easily decomposed in steam at 130 °C and converted to carbonate species. Thus, focusing on the turnover of formate via C–H bond breaking offers important possibilities for future catalyst development.

Graphical Abstract