Modulating the selective adsorption of biobased diol carbon-oxygen bonds for the synthesis of cyclic carbonates

Abstract

The synthesis of cyclic carbonates via carbon-oxygen bond activation of vicinal-diols and linear carbonates via transesterification is significant, but the reaction mechanism remains unclear. Herein, we synthesized 1,2-butene carbonate (1,2-BC) from 1,2-butanediol (1,2-BDO) and dimethyl carbonate (DMC) as a target reaction and investigated the relationship between different CeO₂ crystal effects and acid-base sites. CeO₂-rod exhibits more oxygen vacancies (Ce^3 +-O_v), generating additional Ce³⁺ and O^2- as Lewis acid and base sites, respectively, enhancing the activation of C-O and O-H bonds. CeO₂-R exhibited high activity, achieving a space-time yield of up to 500 g_1,2-BC·h⁻¹·g_cat⁻¹ during 200 h long-term operation. Difficulty in adsorption of the active conformation due to the presence of competing adsorption, in situ DRIFTS revealed that the bridging butoxy-O_v of 1,2-BDO and the cis-cis monodentate adsorption conformation of DMC play a decisive role in the reaction. The presence of key intermediates that are difficult to capture was confirmed for the first time. Molecular dynamics simulations justify the proposed theory of dehydrocyclization of the intermediate hydroxy butylmethyl carbonate to 1,2-BC. The good generalizability of vicinal-diol substrate provides a reference and inspiration for synthesizing cyclic carbonates.