Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol over CexZr1-xO2 and [EMIM]Br/Ce0.5Zr0.5O2

The solid solution series CexZr1-xO2 (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0) with a bimodal pore structure was prepared by the citric acid sol gel method. Results from X-ray diffraction, Raman spectroscopy, scanning electron microscopy, mercury porosimetry, and N-2 adsorption/desorption measurements indicated that the physical properties of the solid solutions were significantly affected by the Ce/Zr molar ratio and the calcination temperatures. These solid solutions can be used in the synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide. Results indicated that the structure of the solid solutions and the Ce/Zr molar I ratio in CexZr1-xO2 were the key factor in determining the catalytic activity for the synthesis of DMC. Higher catalytic performance was observed with a 1:1 Ce/Zr molar ratio at a calcination temperature of 1273 K. 1,1,1-Trimethoxymethane (TMM) was used to remove residual H2O in situ, and was found to increase the methanol conversion from 1.8 to 7.9% at 373 K under a pressure of 20 MPa after 24 h. The combination of the bimodal porous catalyst with an effective H2O removal agent gave a methanol conversion of 10.4% at 373 K, under 12 MPa after 34 h. The catalytic activity was almost doubled when the ionic liquid 1-ethyl-3-methylimidazolium bromide was loaded on Ce0.5Zr0.5O2., which may be a promising means for selective production of DMC from CO2 and CH3OH.