Task-Specific Ionic Liquid Functionalized-MIL-101(Cr) as a Heterogeneous and Efficient Catalyst for the Cycloaddition of CO2 with Epoxides Under Solvent Free Conditions

A novel heterogeneous catalyst was synthesized by immobilization of a carboxylic acid- and imidazolium-based ionic liquid on the mesoporous MIL-101(Cr) (MIL-101(Cr)-TSIL) and used to convert abundant, nontoxic, economical and renewable CO2 gas to cyclic carbonates without the need for a cocatalyst or a solvent. The catalyst was characterized in detail by multiple techniques such as XRD, TEM, SEM, EDX, DR-FTIR, solid-state NMR, as well as N-2 and CO2 adsorption measurements. The catalytic properties were studied by varying different parameters including amount of catalyst and epoxide, temperature, pressure, and reaction time. Under optimal conditions (100 mg catalyst, 15 mmol epoxide, 2.0 MPa CO2 pressure, 110 degrees C and 2 h reaction time) various cyclic carbonates were obtained with high yield and selectivity. MIL-101(Cr)-TSIL catalyst displayed good thermal stability and could be reused after simple separation without a significant decrease in its catalytic activity. Due to synergetic effect of the hydrogen bond from the carboxylic acid group for activation of the C-O bond of the epoxide, adsorption of CO2 by the imidazolium moiety, and high concentration of CO2 around the task specific ionic liquid (TSIL), arisen from the mesoporous framework, MIL-101(Cr)-TSIL is a highly effective catalytic system for the solvent-free cycloaddition of CO2 with epoxide.