Ionic Liquid/Quaternary Ammonium Salt Integrated Heterogeneous Catalytic System for the Efficient Coupling of Carbon Dioxide with Epoxides

A heterogeneous catalytic system featuring multifunctional sites has been constructed through the grafting of an amino-functionalized imidazolium ionic liquid (Si-IM-NH2) and a quaternary ammonium salt (Si-TBAI) on mesoporous cagelike silica SBA-16 for the coupling of carbon dioxide (CO2) with epoxides. The resultant composites SBA-16@IM-NH2 and SBA-16@TBAI, even with much lower Brunauer–Emmett–Teller surface areas than SBA-16, exhibit highly increased CO2 adsorption capacities (i.e., up to 3.13 mmol·g–1 at 80 °C, 3.5 times that of SBA-16). Under the synergistic effect of the good CO2 enrichment ability, multiple active sites (I–, Cl–, −NH2 group, and imidazolium ring), and open mesoporous channels, the catalytic system with a Si-TBAI/Si-IM-NH2 molar ratio of 3:1 can catalyze CO2 into several kinds of cyclic carbonates with excellent yield and selectivity at low temperature and pressure (50 °C and 0.5 MPa) in the absence of any cocatalyst. This catalytic system can be easily recovered and recycled several times without loss of activity, making it a competitive catalyst for CO2 conversion.