Melem based mesoporous metal-free catalyst for cycloaddition of CO2 to cyclic carbonate

Abstract

A highly efficient melem based mesoporous metal-free catalyst with amino and hydroxyl groups was successfully developed by template method with melamine as precursor and nano-SiO2 as template. In the absence of any co-catalyst and solvent, the catalyst mp-CN-450 exhibits high catalytic activity for catalytic cycloaddition reaction between CO2 and polyfunctional epoxides, and the epoxides conversion and corresponding cyclic carbonates selectivity are 99.7 % and 99.5 %, respectively. And the catalyst has hardly loss of catalytic activity after being reused for four cycles. The characterization results disclose that the high catalytic activity of the catalyst is closely related to its large specific surface area, abundant mesoporous structure and synergistic effect of N species and hydroxyl groups of melem hydrates. Additionally, through the study of different N-containing compounds, it was found that the primary amine may underwent a ring-opening reaction with epoxide. But with the addition of CO2, amine groups prior to reacted with CO2 to form carbamate salt, avoided the formation of by-products, thereby improved the selectivity of cyclic carbonate. Finally, based on the above research, a possible reaction mechanism for the coupling of CO2 to epoxides was proposed.