Synthesis of Bifunctional Porphyrin Polymers for Catalytic Conversion of Dilute CO₂ to Cyclic Carbonates

Abstract

Development of efficient solid catalysts for catalytic conversion of dilute CO₂ is of extreme importance for carbon capture and utilization. We report the synthesis of bifunctional polymers co-incorporated with porphyrin-Zn as Lewis acid sites and Br^- as nucleophiles for the cycloaddition of dilute CO₂ with epoxides in this work. It was found that the Br^-/Zn ratio has a volcano relation with the activity of bifunctional polymers in a cycloaddition reaction, indicating the synergy effect between Lewis acid sites and nucleophiles. The turnover frequency (TOF) of the bifunctional polymer is more than four-fold that of the physical mixture of tetrabutylammonium bromide and porphyrin-Zn-incorporated polymer, implying the enhanced cooperation between Br^- and porphyrin-Zn in the polymer network. The bifunctional polymer with optimized Br^-/Zn afforded 99% conversion, 99% selectivity, and a TOF as high as 12,000 h^-1 for the cycloaddition of CO₂ and propylene oxide, which is among the most active solid catalysts ever reported. Furthermore, the bifunctional polymer could efficiently catalyze the cycloaddition of epichlorohydrin with dilute CO₂ (7.5% CO₂ balanced by N₂) even under ambient conditions, demonstrating its potential application in industrial-scale production.