Catalytic conversion of CO2 to cyclic carbonates: A metal-free approach using urea-functionalized ionic salts grafted in ordered mesoporous SiO2

The development of metal-free and high-efficiency heterogeneous catalysts for the chemical conversion of CO 2 into value-added chemicals is crucial for carbon cycling. Here, we report the synthesis of a four-armed urea-functionalized ionic salt that incorporates active bromide ions (Br − ) and urea groups. This salt was subsequently grafted onto ordered mesoporous SiO 2 (SBA-15) to catalyze the cycloaddition reaction between CO 2 and epoxides. The impacts of structure features, grafting density of the urea-functionalized ionic salts, and pore size of SBA-15 on catalytic performance were systematically investigated. The results obtained emphasize that SBA-15–5@TEU(1:1) demonstrates remarkable synergistic catalytic efficacy, facilitating the efficient transformation of various epoxides into cyclic carbonates through cycloaddition reactions in the absence of both solvents and cocatalysts. Notably, this catalyst achieves a maximum yield of up to 99%. Additionally, SBA-15–5@TEU(1:1) demonstrates excellent reusability, with no significant decrease in catalytic activity observed over multiple cycles. Mechanistic studies further elucidate the crucial roles of Br − and urea groups in facilitating the synergistic catalysis of CO 2 cycloaddition reaction. This work presents novel insights the design of metal-free and co-catalyst-free heterogeneous catalysts for efficient CO 2 conversion.