Catalytic Performance of Microwave Functionalized NH<SUB>2</SUB>-MIL-53 for Cyclic Carbonate Synthesis from CO<SUB>2</SUB> and Epoxides

Abstract

The efficacy of microwave irradiation in the quaternization of amino-functionalized MIL-53 metal-organic framework (MOF) as well as the catalytic activity of the resultant MOF in the cycloaddition of carbon dioxide with epoxides under solvent-free conditions has been studied. A series of NH2-MIL-53 were synthesized and quaternized by reacting alkyl halide of various alkyl chains and anions under microwave irradiation. The post-functionalized F-MIL-53-AXs were characterized through solid-state XRD, FT-IR, XPS, and TGA. F-MIL-53-Mel prepared by microwave method showed higher AGC yield than that by the conventional heating method. F-MIL-53-AXs with iodide anion exhibited the best catalytic activity irrespective of the alkyl chain length, in agreement with the generally accepting order of nucleophilicity, Cl<Br<I. A plausible mechanism in which Lewis acidic metal center and quaternary ammonium functional group operate synergistically is proposed. The F-MIL-53-AX catalysts were found to exhibit high thermal stability and were reusable over than three times, without any significant lowering of activity.