Single Ce atom-assisted oxygen vacancies as active and stable sites for CO2 conversion

Oxygen vacancies are often considered the active sites for CO2 conversion, but their engineering to enhance activity and stability has been scarcely investigated, especially at high reaction tempeture (≥600 °C) or under severe stressing conditions (i.e., in presence of H2S). We demonstrate that oxygen vacancies in defective MgO nanocrystals (less than 20 nanometres) can be significantly promoted by the addition of atomically dispersed Ce atoms anchored at these defective MgO sites. These catalysts combine high performance in CO2 conversion with exceptional stability even in the presence of 300 ppm H2S. For a loading <2 wt%, the Ce atoms are exclusively present as isolated species coordinated to oxygen-defective sites of MgO nanocrystals. These Ce single atoms promote the formation of these defects and facilitate the adsorption of CO2, enhancing the activation of H2 molecules, but do not play a role alone as single-atom catalysts. Extensive mechanistic studies, chemical kinetics and theoretical modelling prove that the single-atom-assisted oxygen vacancies (SA-Ov) enables the high catalytic performance and stability, thereby opening new avenues for catalyst design. Oxygen vacancies are key active sites for CO2 conversion, but enhancing their activity and stability under harsh conditions is rarely explored. Here, the authors show that adding atomically dispersed Ce to defective MgO greatly increases vacancy density, leading to superior performance in reverse-water-gas-shift reaction, even with 300 ppm H2S present.