Synthesis of dimethyl carbonate from CO2 and methanol over CeO2 catalysts prepared by soft-template precipitation and hydrothermal method

Direct synthesis of dimethyl carbonate (DMC) from methanol (MeOH) and carbon dioxide (CO2) is a promising environmentally-friendly process for utilizing CO2 as a source of useful chemicals. For this reaction, CeO2 is known as an effective catalyst, and a variety of CeO2 catalysts prepared via various synthetic methods for controlling textural and surface properties of CeO2 such as facets, particle shapes, acidity, basicity, and oxygen vacancies have been employed. In this study, CeO2 catalysts were prepared via the combination of soft-template precipitation and hydrothermal treatment followed by calcination at different temperatures, and their catalytic performance for the DMC synthesis was investigated in the presence of 2-cyanopyridine (2-CP) as a dehydrating agent. CeO2 calcined at 650 °C (CeO2(650)) exhibited the highest DMC yield among the catalysts prepared in this study under the identical conditions. Its catalytic performance represented by the DMC formation rate at 110 °C was 31 mmol gcat−1 h−1 at 5 MPa of CO2 and MeOH/2-CP molar ratio of 1.0, and this rate was comparable to the previously reported highest value of 42 mmol gcat−1 h−1 under the similar reaction conditions consisting of reaction temperature of 110 ± 20 °C, CO2 pressure of 5 ± 1 MPa, and molar ratio of MeOH/2-CP of 0.5–2.0. Among the surface acidity and basicity examined by the temperature-programmed desorption measurements, the amount of base sites with medium strength of the prepared CeO2 catalysts was in the same order as the DMC amount. The infrared spectroscopy for the CO2 species chemisorbed on the CeO2 surfaces suggested the formation of bicarbonate species on the base sites with medium strength.