Enhanced catalytic activity of H2 heat-treated porous ceria for direct conversion of carbon dioxide into dimethyl carbonate

Abstract

It has been demonstrated that the specific surface area, acid–base properties, morphologies, and oxygen-vacancies (Ov) play a role in the catalytic performance of CeO2-based catalysts. In this study, porous CeO2 and Zr-doped CeO2 catalysts with high surface area have been prepared via a low temperature synthesis strategy and evaluated for the conversion of CO2 and methanol into dimethyl carbonate (DMC). Results show that the Zr doping (Zr:Ce = 1:9) could slightly increase the DMC formation rate of CeO2, whereas the H2 heat-treatment of CeO2 could lead to a DMC formation rate of 18.22 ± 0.64 mmol g–1h−1, which is amongst the highest for CeO2 catalysts at 140 °C reported so far. Such enhancement in DMC formation rate is attributed to (1) the balanced crystallinity and defects of the CeO2, (2) a shift of acid and base activity to lower temperature, and (3) the (111) plane only surface termination of the catalyst resulted from the heat-treatment process. Excluding the best performed H2 heat-treated CeO2 catalyst, the DMC formation rate of the rest catalysts shows a positive link to the BET surface area, acid property (NH3-TPD), OV%, Ce3+%, and the Raman peak intensity ratio of ID/IF2g of the catalyst. The low temperature preparation strategy in this study could be applicable to the synthesis of CeO2 catalyst towards other reactions (e.g., non-reductive CO2 conversions to various carbonates, carbamates, urea derivatives, etc.).