Light-Driven CO2 Fixation into Epoxides Using an Al2O3/CoAl2O4 Composite Photocatalyst

Utilization of carbon dioxide (CO2) as a C1 feedstock to synthesize value-added chemicals using a catalyst made from earth-abundant elements and under mild conditions is a sustainable approach toward carbon neutrality but difficult to achieve. Herein, the CoAl2O4/Al2O3 composite catalyst is developed and used for the light-driven epoxide to value-added cyclic carbonate conversion using CO2. CoAl2O4/Al2O3 composite catalysts (x% Co–Al2O3) are prepared by calcining cobalt-incorporated Al-oxy-hydroxide at 500 °C under an air atmosphere. The composite 15% Co–Al2O3 (57% Al2O3 and 43% CoAl2O4) shows the highest photothermal conversion efficiency (η = 66%) as well as catalytic activity toward CO2 fixation into epoxides to generate cyclic carbonates under 1 atm CO2 pressure and solvent-free conditions (300 W xenon lamp). The catalyst displays good selectivity for the synthesis of a series of cyclic carbonates (>95%) with good yield in the presence of tetra butyl ammonium iodide (TBAI) as a cocatalyst (2 mol % with respect to epoxide). Under the optimized reaction parameters, 15% Co–Al2O3 retains its catalytic activity up to 8 cycles of catalysis without losing its chemical integrity. The reaction mechanism is proposed based on a structure–photothermal conversion-catalytic activity relationship study and a few control experiments. The design and development of a photocatalyst from the earth-abundant Al element under user-friendly conditions make this approach sustainable for the CO2 economy.