Integration of polypyridyl-based ionic liquids into MIL-101 for promoting CO2 conversion into cyclic carbonates under cocatalyst-free and solventless conditions

Abstract

It is highly desired yet an enormous challenge to exploit efficient catalysts for epoxide cycloaddition with carbon dioxide to achieve the goal of carbon neutrality. Herein, the novel heterogeneous catalysts of MIL-101-IL(RBr) (R = Et, Pr, Bu, and Pe) were synthesized by grafting polypyridyl-based ionic liquids (IL) into the nodes of MIL-101(Cr) through the post-synthetic modification of metal–organic frameworks (MOFs). The octahedral MIL-101-IL(BuBr) with an average size of ca. 800 nm exhibited superior activity for catalyzing epichlorohydrin–CO₂ cycloaddition into chloropropene carbonate, with an yield of 92% at 110 °C under 1.0 MPa CO₂ without any cocatalyst and solvent. The excellent performance could be attributed to the nucleophilic nature of grafted ionic liquids in the MOF along with the effectiveness of mass transfer afforded by the MOF porosity. Moreover, MIL-101-IL(BuBr) presented a favorable versatility toward other epoxides and a satisfactory recyclability. In addition, a possible mechanism has been proposed for the catalytic reaction of epichlorohydrin–CO₂ cycloaddition over MIL-101-IL(BuBr).