Polymer nanoparticles grafted zinc-containing ionic liquids: A highly efficient and recyclable catalyst for cooperative cycloaddition of CO2 with epoxides

A series of cross-linked polymer nanoparticles grafted zinc-containing imidazolium ionic liquids (PNPs-Im(2)ZnBr(2)X(2), X = Cl, Br, and I) were designed and facilely synthesized. Evaluated in chemical fixation of CO2 with epoxides into cyclic carbonates in the absence of any solvent and co-catalyst, the PNPs-Im(2)ZnBr(2)X(2) showed high and stable activity, superior to other mostly reported ionic liquid catalysts. The effects of reaction temperature, CO2 pressure, reaction time and the loading of catalyst on the synthesis of propylene carbonate (PC) from CO2 and propylene oxide were investigated. Under the optimized reaction conditions, PNPs-Im(2)ZnBr(2)I(2)-1 showed the highest catalytic activity, and PC was yielded to 95.5% with 99.5% of selectivity and 1910 h(-1) of TOF. In the cycloaddition reaction of CO2 and epoxides, the catalysts shows good chemical stability, and can be separated conveniently from the products after reaction and reused for five runs without significant loss of activity. It is suggested that the superior catalytic performance of the as-fabricated catalysts may be attributed to the synergistic effects of zinc atom, imidazolium cation, and halide anion on the activation of epoxide and CO2, respectively. Due to the excellent stability, activity, and recyclability, the PNPs-Im(2)ZnBr(2)X(2) catalysts have broad prospects for the practical conversion of CO2 in chemical industry.