Combination of binary active sites into heterogeneous porous polymer catalysts for efficient transformation of CO2 under mild conditions

Abstract

The transformation of CO2 into cyclic carbonates via atom-economical cycloadditions with epoxides has recently attracted tremendous attention. On one hand, though many heterogeneous catalysts have been developed for this reaction, they typically suffer from disadvantages such as the need for severe reaction conditions, catalyst loss, and large amounts of soluble co-catalysts. On the other hand, the development of heterogeneous catalysts featuring multiple and cooperative active sites, remains challenging and desirable. In this study, we prepared a series of porous organic catalysts (POP-PBnCl-TPPMg-x) via the copolymerization metal-porphyrin compounds and phosphonium salt monomers in various ratios. The resulting materials contain both Lewis-acidic and Lewis-basic active sites. The molecular-level combination of these sites in the same polymer allows these active sites to work synergistically, giving rise to excellent performance in the cycloaddition reaction of CO2 with epoxides, under mild conditions (40 °C and 1 atm CO2) in the absence of soluble co-catalysts. POP-PBnCl-TPPMg-12 can also efficiently fixate CO2 under low-CO2-concentration (15% v/v N2) conditions representative of typical CO2 compositions in industrial exhaust gases. More importantly, this catalyst shows excellent recyclability and can easily be separated and reused at least five times while maintaining its activity. In view of their heterogeneous nature and excellent catalytic performance, the obtained catalysts are promising candidates for the transformation of industrially generated CO2 into high value-added chemicals.