In-situ synthesis of a heterogeneous NHC–CO2 catalyst for continuous DMC production

Abstract

N-heterocyclic carbene CO₂ adducts (NHC–CO₂) are typical zwitterionic ionic liquid compounds, known for their strong nucleophilicity and significant catalytic ability. However, NHC–CO₂ is sensitive to water, and its complex and polluting preparation process limits its widespread application. Furthermore, most reported NHC–CO₂ compounds function as homogeneous catalysts, posing considerable challenges for separation. In this study, an in-situ green synthesis method was employed to develop a heterogeneous NHC–CO₂ catalyst, PS–IMIL. This approach not only prevents direct contact between the catalyst and water but also simplifies the preparation process and mitigates environmental pollution. The synthesis conditions of PS–IMIL were optimized, and its structure and properties were analyzed. Furthermore, the synthesis mechanism of PS–IMIL was investigated, and its kinetics were also studied. The results indicate that the interaction between the material ethylene carbonate (EC) and the precursor is crucial for the in-situ synthesis of PS–IMIL. The prepared PS–IMIL not only preserves the catalytic ability of NHC–CO₂ but also exhibits characteristics of being metal- and halogen-free. Remarkably, the catalytic activity and structure of PS–IMIL remain unchanged after 300 h of continuous use in dimethyl carbonate (DMC) production. Compared to similar catalysts, PS–IMIL exhibits excellent catalytic activity and stability. This study provides a solid theoretical and practical reference for the development of heterogeneous NHC–CO₂ catalysts. The synthesized PS–IMIL demonstrates significant potential for the industrial production of DMC and other carbonate esters.