Silica grafted imidazolium-based ionic liquids: efficient heterogeneous catalysts for chemical fixation of CO2 to a cyclic carbonate

Imidazolium-based ionic liquids with varied alkyl chain lengths bearing different anions (Cl-, Br- and I-) were synthesized and immobilized onto the commercial silica surface (IMIS). These heterogeneous catalysts exhibited high catalytic activities and selectivities in the cycloaddition of carbon dioxide to allyl glycidyl ether (AGE). The immobilized ionic liquids with longer alkyl chain length and more nucleophilic anion showed higher activity. In particular, compared with pristine IMIS, zinc halide-combined IMIS (IMIS-Zn) with Cl- exhibited an increased activity, while the IMIS-Zn with Br- and I- showed lower activity than IMIS itself. In addition, the textures of silica supports (surface area and average pore size) have a great impact on the catalytic activity owing to the substance-confined diffusion effects. The recycling experiments showed that the resulting heterogeneous catalysts exhibited good reusability.