Activation of carbon dioxide with surface oxygen vacancy of ceria catalyst: An insight from in-situ X-ray absorption near edge structure analysis

The concentrations of oxygen vacancy (Ov) and trivalent Ce ions (Ce3+) have been widely recognized as key reactivity descriptors to the CeO2-based catalysts. Nonetheless, the Ov and Ce3+ concentrations of CeO2-based catalysts are often determined by ex-situ characterizations without considering their interactions with reactants, a situation that is difficult to reflect their effective amounts participated in the catalytic process. In this study, a series of CeO2 catalysts with varied Ov and Ce3+ concentrations were prepared by a hydrothermal method followed by calcination at different temperatures. These CeO2 catalysts were characterized and assessed by the synthesis of dimethyl carbonate (DMC) from the reaction of CO2 and methanol. Using in-situ X-ray absorption spectroscopy without and with CO2 adsorption, the quantitative analysis of effective Ce3+ (associated with surface Ov) present in CeO2 catalysts for DMC synthesis is achieved. These results shed light on the critical role of surface Ov in CeO2 catalysts for non-reductive conversion of CO2 as well as the importance of in-situ characterizations for effective Ov and Ce3+ concentrations in CeO2 catalysts.