Influence of Metal Ions on Metal-Organic Frameworks for Cocatalyst-Free Carbon Dioxide Conversion.

Metal-organic frameworks (MOFs) stand out as a preferred category of materials owing to their remarkable tunability and design flexibility for targeted applications. The fixation of carbon dioxide (CO2) into value-added chemicals, such as cyclic carbonates, often requires the use of cocatalysts. Herein, a series of MOFs were synthesized under solvothermal conditions by reacting 2,5-dibromoterephthalic acid (DBTA) with metal ions (M = Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+), termed M-DBTA. The choice of metal ions in M-DBTA plays a pivotal role in tuning structural attributes and catalytic efficiency. The synergistic interplay between CO2 affinity and acidic sites enhances catalytic performance in the CO2 conversion into cyclic carbonates at atmospheric pressure, without cocatalysts or solvents. Mn-DBTA and Co-DBTA achieve higher catalytic activity for the formation of 4-(chloromethyl)-1,3-dioxolan-2-one (achieving yields of 85% and 87%, respectively) from the reaction of CO2 with epichlorohydrin. This superior activity is attributed to the strong CO2 affinity (Qst) of Co-DBTA (47.8-28.9 kJ mol-1) and Mn-DBTA (16-28 kJ mol-1), along with Lewis acidic sites. The low kinetic barrier further facilitates CO2 conversion, as supported by thermodynamic parameters. Notably, Co-DBTA shows recyclability, maintaining structural integrity over four cycles. These findings highlight the potential of MOFs for sustainable CO2 conversion under mild conditions, paving the way for future advancements in catalytic design.