Ionic Liquids Grafted Mesoporous Silica for Chemical Fixation of CO2 to Cyclic Carbonate: Morphology Effect

Three mesoporous silica materials (MCM-41, MSN and BMMs) possessing different morphologies but similar hexagonal arranged mesopores with almost the same pore size (2-3 nm) were functionalized by Zn and [1-(trimethoxysilyl)propyl-3-methylimidazolium] ionic liquid (ILs) via post-grafting treatment. The ILs grafted mesoporous silicas were then characterized by porosity, microscopy and SAXS techniques, and the successful loading of Zn and ILs, as well as the different distribution of functional groups in different supports were shown. Furthermore, the cycloaddition reaction of CO2 with epoxide was employed to evaluate the influences of the ILs distribution, which was proved to be caused mainly by varying morphologies of different supports. All the catalysts showed good catalytic activities. Interestingly, at low temperature, the inter particle supported ILs in BMMs had the highest catalytic efficiency, while the aggregation grafting ILs on MCM-41 present the lowest activity. However, the mesoporous silicas with ordered arranged nanopores present the superiority at higher temperature. The results highlight the crucial role played by the morphology of the supports.