Highly Efficient CO₂ Fixation Into Cyclic Carbonates Catalyzed by Imidazolium-Functionalized Zn-Based MOFs

Abstract

The coupling between epoxide and carbon dioxide into cyclic carbonates in the absence of co-catalyst and solvents is a feasible strategy for removing CO₂ from the atmosphere and achieving a carbon-neutral cycle. In this context, two new bifunctional catalytic systems prepared by modification metal–organic frameworks (MOFs) with ionic liquids (ILs) and catalytic activities have been compared in converting CO₂ into cyclic carbonates. IL methylimidazolium bromide (MI-Br) is grafted into both Zn-MOF-NH₂ and Zn₃(L)₃(H₂L) MOF to produce the dual-functional one-component systems with a high density of Lewis acidic Zn(II) metal sites and IL functional sites to carry out co-catalyst/solvent-free cycloaddition of CO₂ to epoxides. The characteristics of the MI-Br IL@MOFs were revealed via different techniques, including FE-SEM, EDX, FT-IR, XRD, N₂ adsorption, NH₃-TPD, and ICP-OES. Further, two efficient catalysts act as excellent recyclable catalysts for 4 successive cycles without substantial loss in catalytic activity cycloaddition of CO₂ to epoxides to cyclic carbonates. Herein, a synergistic catalytic mechanism between Lewis acidic sites and Br⁻ ions is proposed to carry out the cycloaddition of CO₂ to epoxides under co-catalyst/solvent-free conditions.