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 (Q_st) 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.