Design of Nitrogen-Containing Mixed Ligand-Modified Mesoporous Metal–Organic Frameworks for Efficient CO₂ Conversion under Simulated Ambient Conditions

The conversion of CO2 from flue gas with epoxide [cycloaddition epoxide (CCE)] to produce cyclic carbonate is one of the important technologies to mitigate CO2 emissions. In this context, a bifunctional mesoporous MOFs-based catalyst, Al-MDC-NC, was synthesized, which is composed of Al3+ Lewis acid sites and two nitrogen-containing mixed ligands that can capture CO2. By grafting an N atom on the imidazole group to form a specific N-heterocyclic carbene-carboxylic adduct (NHC-CO2) as the Lewis base site and introducing an electron-withdrawing group of NO2 to enhance the Lewis acidity of the Al3+ sites, the carbon dioxide capture ability and the polarization of the epoxy substrate are improved in the absence of cocatalysts. The CCE reaction of CO2 and epichlorohydrin shows a good catalytic effect, and a high conversion rate of 95.80% is obtained under mild and energy saving reaction conditions (100 °C, 10 h, and 1 bar). Interestingly, even for simulated dry and humid CO2 flue gases, the conversion rates are as high as 90.35% and 83.99%, respectively. In addition, Al-MDC-NC, as a heterogeneous catalyst, shows a very robust structure and recyclability after five cyclic catalytic experiments. This study may provide an effective avenue for the production of value-added fine chemicals from industrial flue gas under actual ambient conditions using a ligand modification strategy.