Integration of metalloporphyrin into cationic covalent triazine frameworks for the synergistically enhanced chemical fixation of CO2

Abstract

The design and preparation of porous catalysts with multiple catalytically active sites for synergistically catalytic conversion of CO₂ still remains a challenge. Herein, cobalt porphyrin as a Lewis acidic active site was introduced in imidazolium-functionalized cationic covalent triazine frameworks (denoted as Co-PCCTFs) via copolymerization of cobalt 5,10,15,20-tetrakis(4-cyanophenyl)porphyrin (Co-TPPCN) and 1,3-bis(4-cyanophenyl) imidazolium chloride ([BCIM]Cl). The obtained bifunctional Co-PCCTFs with positively charged imidazolium groups have high BET surface areas and show sufficient CO₂ adsorption uptakes. The nucleophilic halide anions of the imidazolium parts and the cobalt porphyrin Lewis acid sites were positioned in close proximity so that the Co-PCCTFs could synergistically activate substrates and intermediates. Compared with ICTF-400 free of Co²⁺ that was obtained from [BCIM]Cl, Co-PCCTF₅ exhibited enhanced activity for the cycloaddition of CO₂ to epoxides to produce cyclic carbonates without a cocatalyst under mild conditions. Moreover, Co-PCCTF₅ is sufficiently stable so that it could be reused more than 5 times without loss of catalytic activity. This work provides a new approach for the design and preparation of efficient multifunctional catalysts with multiple sites for synergistic catalysis.