Efficient Reduction of CO₂ via Modified Bimetallic Metal–Organic Frameworks-Based Cycloaddition under Mild Conditions

The incorporation of functionalized secondary metal nodes into bimetallic metal–organic frameworks (MOFs) enhances their performance and application potential. This study investigates Cu/Zn-MOF-74 catalysts with varying metal ratios for carbon dioxide (CO₂)-epoxide cycloaddition. Compared to monometallic Cu-MOF-74 and Zn-MOF-74, the bimetallic system shows superior catalytic activity for epoxides conversion. Vim─COOH@Cu/Zn-MOF-74 is developed by introducing hydrogen bond donors (HBD) and nitrogen-containing linkers. The optimal Vim─COOH@Cu₀.₆₇Zn₀.₃₃-MOF-74 demonstrates outstanding performance in CO₂-epichlorohydrin cycloaddition, achieving 96.4% conversion and 98.5% selectivity under mild conditions (80 °C, 1.0 MPa, 24 h) without co-catalysts, while maintaining excellent recyclability. Using a one-pot synthesis, bimetallic MOFs with controlled Cu/Zn ratios are prepared. The framework is further modified by incorporating 1,4-butanediyl-3,3′-bis-1-vinylimidazolium bromide and HBD-functionalized imidazole bromide monomers. The resulting composites achieve over 80% conversion under solvent-free, co-catalyst-free conditions due to synergistic effects between Lewis acid sites, carboxyl groups, and nucleophilic Br⁻ ions. This work presents an effective strategy for developing efficient MOF catalysts for CO₂ conversion. The Vim─COOH@Cu/Zn-MOF-74 system demonstrates significant potential for sustainable CO₂ utilization in cyclic carbonate synthesis, combining high activity, selectivity, and stability under environmentally friendly reaction conditions.