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

The solid solution series Ce x Zr 1- x O 2 ( 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 ratio in Ce x Zr 1- x O 2 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 H 2 O 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 H 2 O 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 Ce 0.5 Zr 0.5 O 2, which may be a promising means for selective production of DMC from CO 2 and CH 3 OH.