Ordered mesoporous carbon encapsulated linear poly(ionic liquid)s enabling synergy effect of surface groups and ionic moieties for CO2 fixation under mild conditions

Abstract

Carbon dioxide (CO₂) fixation into value-added chemicals has attracted growing attention and one promising atom-efficient pathway is via the cycloaddition with three member-ring compounds like epoxides. Herein, we demonstrated that encapsulation of linear poly(ionic liquid)s (PILs) on ordered mesoporous carbon materials provides a facile and feasible approach towards environmental-friendly heterogeneous catalysts with high performance in CO₂ cycloaddition with epoxides under mild conditions. A series of novel linear phenolic hydroxyl group functional imidazolium-based PILs synthesized from hydroxymethylation reaction between 4-(imidazol-1-yl)phenol-1-butyl-imidazolium iodide and formaldehyde was loaded on ordered mesoporous carbon FDU-15–600 derived from mesoporous phenolic resin. By virtue of controlling the initial polymerization temperature, the molecular weight of PILs was facilely modulated, reaching strong host–guest interaction during the PIL immobilization. Highly stable immobilized PIL species with spatial satisfaction of ionic moieties and surface groups were thus realized to enable a synergic CO₂ conversion via cycloaddition with epoxides. The optimal catalyst exhibited high yield and stable recyclability by using atmospheric CO₂ under metal-additive-solvent-free conditions and the activity surprisingly exceeded the corresponding homogeneous parent IL and PIL. Excellent substrate compatibility was found by extending the transformation of more than ten epoxides including the inert ones such as disubstituted cyclohexene oxide. The significantly enhanced activity is attributed to the synergistic effect of the surface hydrogen groups and ionic moieties to accelerate the rate-determining ring-opening process.