Synergistic strategy for constructing highly efficient MOF aerogel catalysts for co-catalyst-free CO2 cycloaddition.

Supported metal-organic framework (MOF) aerogels combine the advantages of multiple carrier catalysts through synergistic effects, enabling efficient CO2 cycloaddition reactions and exhibit significant potential for practical applications. We prepared a set of MOF aerogel catalysts by means of a secondary synthesis method that combined freeze-drying with subsequent spraying. The catalysts included Cu- and Zn-based monometallic MOFs, Cu/Zn bimetallic MOFs, and composites doped with corncob pyrolyzed biochar. These materials were further functionalized via post-synthetic modification with tris(2-aminoethyl)amine (TREN). Their catalytic performance was evaluated in the CO2-epoxide cycloaddition reaction in the absence of co-catalysts or solvents. Under the conditions of 80 °C, 1 bar CO2, 24 h, and 150 mg of catalyst, bimetallic Cu/Zn MOFs showed higher conversion of epichlorohydrin (ECH) than their monometallic counterparts. Furthermore, both carbon-doped MOFs and polyamine-modified samples exhibited improved conversion rates. Among them, the Cu/Zn-MOF-74 aerogel modified with both C-doping and TREN exhibited superior catalytic performance, delivering a conversion rate of 70.94% and a selectivity of 93.94%. This superior performance in epoxide group activation can be ascribed to the synergy created by the bimetallic design combined with multiple modifications. Biochar acts as an electron donor/acceptor and supplies high porosity and surface functional groups. TREN introduces abundant amine binding sites; nucleophilic amines attack the β-carbon of ECH to facilitate ring-opening. These findings demonstrate the potential of MOF-based heterogeneous catalysts and enhance their efficiency and practicality for industrial applications in CO2 conversion.