Multi-variate metal organic framework as efficient catalyst for the cycloaddition of CO2 and epoxides in a gas-liquid-solid reactor

Abstract

The synthesis of heterogeneous catalysts with multiple active sites for the synthesis of cyclic carbonate from epoxide and CO2 has long been of great interest. Herein, we synthesized zinc metal-based multi-variate metal organic frameworks (MOFs) by incorporating different functionalized ligands into a single framework. Chemically functionalized 1,4-benzenedicarboxylic acid (BDC) in the forms of 2-aminoterephthalic acid (NH2-BDC) and 2-hydroxyterephthalic acid (OH-BDC) were combined to form different sets of multi-variate MOFs. The heterogeneous multi-variate MOF, denoted as MOF-5-MIX, was found to be catalytically efficient toward the coupling reaction between epoxide and CO2 under moderate reaction conditions, with >99% selectivity toward cyclic carbonates under solvent-free conditions in a gas-liquid-solid reactor. Herein we demonstrated the advantages of functional groups in the multi-variate framework, which could provide efficient synergistic sites in accelerating the epoxide-CO2 cycloaddition reaction. The MOF-5-MIX exhibited higher catalytic activity (ECH conversion: 98%, temperature: 50 °C, time: 6 h) than other prepared catalysts (MOF-5, MOF-5-NH2, MOF-5-OH). MOF-5-MIX is a promising catalyst system which is capable to catalyze the synthesize of cyclic carbonates under high reaction temperatures (120 °C) without the presence of TBAB as well as at the lower reaction temperature (50 °C) in the presence of TBAB. Comparison with recently reported MOF catalysts revealed that MOF-5-MIX had better catalytic potential. In addition, a plausible reaction mechanism for the MOF-5-MIX catalyzed reaction is proposed that is supported by previously reported experimental results.