Mesoporous silica-supported ionic liquids as catalysts for styrene carbonate synthesis from CO₂

Various types of mesoporous silica were used as carriers to synthesize a series of immobilized imidazolium-based ionic liquids. Their activity was tested in the synthesis of styrene carbonate from CO₂ and styrene. This is one-pot process, whereby two stages are carried out in one reactor and there is no need to isolate the intermediate product, epoxide. A systematic study on the influence of parameters such as temperature, the reaction time, CO₂ pressure, as well as the amount and type of catalyst used was carried out. A strong synergistic catalytic effect of ionic liquid and Lewis acid was observed in promoting this reaction. The addition sequence of regents and amount of immobilized catalyst were considered crucial for the synthesis of styrene carbonate from CO₂ and styrene. The tested silica-supported ionic liquids gave an easily-recyclable system which under the most favorable conditions ([mtespim]Cl/@SiO₂; ZnBr₂, 0.1 mol%; 110^◦C, 4 h, 1 MPa) can be reused without a significant loss of catalytic activity nor selectivity.