Montmorillonite-Supported Ionic Liquid and Choline chloride as Heterogeneous Catalysts for Efficient CO2 Cycloaddition to Cyclic Carbonates

Abstract

The sustainable conversion of carbon dioxide (CO2) into value-added chemicals is a major concern in modern green chemistry. Here, we present the design and catalytic performance of two highly active heterogeneous systems for the sustainable CO2 cycloaddition with epoxides to afford cyclic carbonates. 1-Butyl-3-methylimidazolium bromide (BMIM-Br) and choline chloride (ChCl) as were immobilized on montmorillonite (MMT), creating robust catalytic systems that combine the high surface area of clay with the unique activity of BMIM-Br and ChCl. Detailed chemical, spectroscopic, and thermal analyses confirmed successful immobilization and excellent structural integrity of both catalysts. Using epichlorohydrin (ECH) as the epoxide under optimized conditions (160 °C, 1.2 MPa CO₂, 4 h), the MMT-supported BMIM-Br and ChCl catalysts achieved outstanding epoxide conversions of 98.2% and 100%, respectively. The superior performance of ChCl/MMT is attributed to the hydroxyl group, which facilitates epoxide activation and ring-opening through hydrogen-bond interactions. Notably, both catalysts exhibited appropriate recyclability over five consecutive runs without major loss of activity, indicating their practical applicability for sustainable processes.