From Trash to Treasure: Probing Cycloaddition and Photocatalytic Reduction of CO2 over Cerium-Based Metal–Organic Frameworks

Fixing the greenhouse gas CO2 via cycloaddition reactions to value-added cyclic carbonates or photocatalytic reduction of CO2 to produce desirable fuels is the most coveted, although challenging, energy-efficient valorization technique owing to the chemical and thermodynamic stability of CO2. Therefore, catalytic materials with an optimum amount of surface porosity and Lewis acidity and basicity play an instrumental and crucial role in CO2 activation in the CO2 fixation reaction. On the other hand, the efficacy of the photocatalytic reduction of CO2 depends on the appropriate band alignment of the catalytic materials and the competitive H2 evolution reaction. Here, we have synthesized Ce-MOFs with and without amine functionalization and compared both MOFs for CO2 fixation with epoxides and photocatalytic reduction of CO2. The amine-functionalized MOF, Ce-BDC-NH2, not only exhibited efficient CO2 fixation to produce cyclic carbonate at room temperature and pressure but also demonstrated effective photoreduction of CO2 with high selectivity toward CH3OH and HCO2H. The probing of the physical properties of the MOFs unveiled that due to the optimum amount of Lewis acidic site Ce3+ and Ce4+, Ce-BDC-NH2 could effectively adsorb the epoxide for the CO2 cycloaddition reaction, whereas the amino functionalization highly influenced the band maxima and minima to facilitate the photoreduction of CO2 with minimized H2 evolution reaction.