Heterogenization of a Green Homogeneous Catalyst: Synthesis and Characterization of Imidazolium Ionene/Br–Cl–@SiO2 as an Efficient Catalyst for the Cycloaddition of CO2 with Epoxides

A promising new strategy for immobilizing a water-soluble oligomeric ionic liquid by coating the ionic liquid with mesoporous silica was established. The immobilized ionic liquid (IL@SiO2) exhibited a good catalytic activity for the production of cyclic carbonates through the cycloaddition of different epoxides with CO2 under solvent-free conditions. The IL@SiO2 catalyst was characterized by different techniques such as FTIR spectroscopy, XRD, TG analysis, FESEM-EDX spectroscopy, map analysis, BET analysis, and TEM. Use of 30 mg of the IL@SiO2 catalyst, which contained 0.023 mmol of the oligomeric ionic liquid IL-3, resulted in a yield of cyclic carbonate with styrene oxide of greater than 95% and a selectivity to the cyclocarbonate of almost 100%. We realized that the hydroxyl groups on the surface of silica could play an important role in the reaction through the hydrogen-bonding interactions between the epoxides and the hydroxyl groups. Moreover, the prepared catalyst was very stable under the reaction conditions and reusable for at least five runs without a considerable change in the yield of the reaction. The effects on the formation of cyclic carbonates of different factors, such as pressure, time, amount of catalyst, and temperature, were investigated.