Direct synthesis of organic carbonates from the reaction of CO₂ with methanol and ethanol over CeO₂ catalysts

The catalytic properties of CeO₂ catalysts in direct synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ were investigated. The formation rate of DMC over the catalysts calcined at 873 K and above was almost proportional to the surface area of catalysts. However, CeO₂ calcined at 673 K showed lower activity than expected from the surface area. From the results of catalyst characterization, CeO₂ calcined at 673 K contained considerable amount of amorphous phase. In contrast, the ratio of amorphous phase decreased on the catalysts calcined at 873 K and above. This suggests that stable crystallite surface is active for the reaction. In the CH₃OH + C₂H₅OH + CO₂ reaction at low temperature, ethyl methyl carbonate (EMC) was formed, and selectivity of EMC formation was comparable to that of DMC. The formation route is discussed by the comparison with transesterification reaction.