Abstract: The reaction of CO₂ with epoxides to form cyclic carbonates requires a catalyst with high-performance, low-cost and easy recovery. A metal-organic frameworks (MOFs)-based heterogeneous catalyst (MIL-101@PIL) was prepared for catalytic conversion of CO₂ to cyclic carbonates. Firstly, the MOF precursor MIL-101-Cr was prepared by hydrothermal synthesis, and then biquaternary phosphonium ionic liquid (1,4-bis-triphenylphosphonium butane bromide) with large molecular volume was loaded into its pore channel to form the catalyst MIL-101@PIL. A series of comparative experiments showed that the catalyst MIL-101@PIL had high activity in the synthesis of cyclocarbonate by cycloaddition reaction without solvent and co-catalyst. Under the optimum conditions (MIL-101@PIL mass of80 mg, CO₂ pressure of 1.4 MPa,propylene oxide amount of 17 mmol, reaction temperature of 90 ℃, reaction time of 3 h), higher yield (95%) and selectivity (99%) were obtained. The results showed that the catalyst (MIL-101@PIL) had high catalytic activity, which was mainly due to the synergistic catalysis between the coordination unsaturated Cr sites and the Br anions. Based on this, a possible mechanism of cycloaddition reaction catalyzed by catalyst MIL-101@PIL was proposed.

Key words: metal-organic frameworks, ionic liquids, cyclic carbonates, carbon dioxide, cycloaddition