Sustainable Production of Cyclic Carbonates from CO 2 and Epoxides Using Transition Metal Substituted Polyoxometalate-TBA Hybrid Catalysts

Abstract

Transition metal substituted polyoxometalates (TMS-POMs) are well recognized for their catalytic characteristics due to their fascinating chemical and physical properties resulting from unparalleled adaptability and structural variety. The interaction of these TMS-POMs with the bulky organic cations enhances the catalytic efficiency with the change in morphology. In this work, we used three hybrid materials of transition metal (Co2+, Ni2+, Cu2+) substituted lacunary Keggin polyoxometalate with tetrabutylammonium cations. The formation and structural features of hybrid materials have been studied by powder XRD, TGA, SEM, TEM, FTIR, and 31P NMR. These hybrid catalysts have been used for the atom-economic coupling of carbon dioxide (CO2) with epoxides to produce cyclic carbonates at incredibly mild circumstances, such as room temperature and atmospheric pressure. The method described here allows for the rapid and effective quantitative conversion of several aliphatic, cyclic, and aromatic epoxides to their respective cyclic carbonates in solvent-free conditions. The cobalt substituted hybrid catalyst shows the highest activity and selectivity with a minimum quantity of 0.12 mol% adequate to provide 85% conversion in 3 h at room temperature. The catalyst is recovered and reused up to four cycles without a drastic loss in activity, hence providing long-term solutions for climate change and environmental concerns.