Porous organic polymers containing zinc porphyrin and phosphonium bromide as bifunctional catalysts for conversion of carbon dioxide

Abstract

Cycloaddition reaction using CO2 as a starting material to form a cyclic carbonate has been applied to chemical fixation of CO2. In order to further increase the reaction efficiency, herein, a bifunctional catalyst (CPBrs) containing metalloporphyrin and quaternary phosphonium salt groups was prepared, and the related catalytic performance for CO2 conversion was also studied. The catalytic system possesses multiple active sites of zinc porphyrin (Lewis acids) and quaternary phosphonium bromide salts (nucleophilic reagents), which can cooperatively work together to enhance the efficiency of cycloaddition reaction. At the same time, CPBrs (CPBr-1 and CPBr-2) are microporous polymers with permanent microporous pore structure and high specific surface areas (342–370 m2 g−1). Their moderate capacities (5.76 and 8.81% at 1 bar/273 K) to capture carbon dioxide were also beneficial for CO2 conversion. The activity of the bifunctional catalyst is higher than that of the catalyst with a single component. The corresponding highest yield to catalyze cycloaddition reaction between methyl substituented propylene oxide and CO2 is up to 95% (2.5 MPa, 90 °C). What is more, the porous nature of catalysts provides the recoverability of the catalyst, and the efficiency of the catalyst CPBr-2 remains high (above 90% yield) after five catalytic recycle.