Oxygen vacancy-hydroxyl frustrated Lewis pairs enabling CO2 cycloaddition for halogen-free synthesis of cyclic carbonates

Abstract

Electronic-grade cyclic carbonates, synthesized via the cycloaddition of CO₂ with epoxides, are important reagents widely used as lithium-ion battery electrolytes, polar aprotic solvents, and polymer monomers. However, current manufacturing processes rely on halide-containing catalysts, which lead to equipment corrosion and high energy consumption during product purification. The development of halogen-free catalysts is significant for enabling a greener upgrade of cyclic carbonate production. Here, a series of O_v-induced surface hydroxylated cobalt oxide catalysts (Co₃O_4−x(OH)_y-T) were developed. Unique frustrated Lewis pair (FLP) structures consisting of O_vs and terminal hydroxyl groups attached to adjacent coordinately-unsaturated cobalt (O_v–cus.Co–OH_t) were successfully fabricated on the O_v- and hydroxyl-enriched cobalt oxide surfaces. The most FLP-abundant catalyst, Co₃O_4−x(OH)_y-170, shows excellent catalytic activity, achieving 95% yield of butylene carbonate and 99% yield of propylene carbonate under halogen-free conditions. Experimental and DFT calculation results reveal that the FLP structures not only improve CO₂ adsorption but also favor intermediate desorption via forming a metastable d-HCO₃ species, which breaks the tradeoff between CO₂ adsorption and intermediate dissociation and enhances the catalytic activity of the developed cobalt oxide catalysts. The findings in this work provide a novel strategy for the green synthesis of cyclic carbonates.