Supported Ionic Liquids For Catalyzing CO₂ Into Cyclic Carbonates

CO₂ is an abundant and inexpensive C1 resource,the preparation of cyclic carbonates by cycloaddition of CO₂ with epoxides has attracted a lot of attention due to its environmental friendliness and atomic economy.Researchers have developed a variety of catalysts for catalyzing CO₂ cycloaddition,among which ionic liquids as homogeneous catalysts can catalyze cycloaddition reactions efficiently.But this catalytic system suffers from difficult catalyst recovery,so there is a need to develop new supported ionic liquids catalysts.In this work,several methods of supported imidazolium-based ionic liquids were explored to prepare heterogeneous catalysts for catalyzing CO₂ into cyclic carbonates using MCM-41 as the carrier.The main studies are as follows.（1）A kind of heterogeneous catalyst MCM-41-S-Im Br has been prepared by grafting imidazolium-based ionic liquids on the surface of MCM-41.The characterization results showed that the ionic liquids were successfully grafted on MCM-41 with intact mesoporous structure and average particle size of 1.4μm.Moreover,the catalyst exhibited high catalytic activity for catalyzing CO₂ into cyclic carbonates without co-catalyst,due to the synergistic effect of the imidazole ring and Br^-.The conversion of epichlorohydrin（ECH）and the selectivity of cyclic carbonate was 98.5%and 98.3%,respectively,at 130℃under 1.6 MPa for 6 h.It is proved that MCM-41-S-Im Br could be used at least 4 times without obviously decreasing in reaction activity.Reaction kinetic study indicated that the approximate rate constant was 0.36 h^-1.（2）Two kind of heterogeneous catalysts were prepared:IL@MCM-41-SI was prepared by encapsulating ionic liquids with silicone ester modified MCM-41 and IL@MCM-41-AM was prepared by encapsulating ionic liquids with amide-modified MCM-41.XRD results showed that both catalysts have mesoporous structures and FT-IR results showed that the ionic liquids were successfully loaded into MCM-41.Both catalysts were used to catalyze the cycloaddition of ECH and CO₂ at 120℃under 1.6 MPa for 6 h with 0.10 g catalyst,respectively.The results showed that the highest catalytic activity of IL@MCM-41-SI and IL@MCM-41-AM was 97.8%and 90.6%,respectively.However,hot filtration experiments showed that the ionic liquids encapsulated by both methods were lost during the cycloaddition reaction.