Facet Engineering in Constructing Lewis Acid-Base Pairs for CO₂ Cycloaddition to High Value-Added Carbonates

Cycloaddition of epoxides with CO2 to synthesis cyclic carbonates is an atom-economic pathway for CO2 utilization with promising industry application value, while its efficiency was greatly inhibited for the lack of highly active catalytic sites. Herein, by taking BiOX (X=Cl, Br) with layered structure for example, we proposed a facet engineering strategy to construct Lewis acid-base pairs for CO2 cycloaddition, where the typical BiOBr with (010) facets expose surface Lewis acid Bi sites and Lewis base Br sites simultaneously. By the combination of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations, the oxygen atom of the epoxide is interacted with the Lewis acid Bi site to activate the ternary ring, then facilitates the attack of the carbon atom by the Lewis base Br site for the ring-opening of the epoxide, which is the rate-determining step in the cycloaddition reaction. As a result, the BiOBr-(010) with rich surface Lewis acid-base pairs showed a high conversion of 85% with 100% atomic economy in the synthesis of cyclic-carbonates without any cocatalyst. This study provides a model structure for CO2 cycloaddition to high value-added long chain chemicals.