Catalytic performance of zinc containing ionic liquids immobilized on silica for the synthesis of cyclic carbonates

Cycloaddition of carbon dioxide and epoxides was investigated using zinc halide based Lewis acidic ionic liquids (ILs) as catalysts. ILs such as 1-butyl-3-methylimidazolium bromide (BMImBr), 1-butylpyridinium bromide (BPyBr), tetra-n-butylammonium bromide (TBABr) were mixed with zinc halide and supported on silica gel to produce heterogeneous catalysts. Catalytic reaction tests demonstrated that the incorporation of zinc ions can significantly enhance the catalytic activity of the silica-supported ILs for the cycloaddition of CO2 to epoxides in solvent-free conditions. BPyBr-ZnCl2/SiO2 showed the highest propylene carbonate yield of 98% when the reaction was carried out with 0.5 g of catalyst at 120 °C at 1.89 MPa of CO2 pressure for 4 h. The immobilized zinc containing IL catalyst could be reused for at least four cycles without any considerable loss of its activity.