Unraveling the effect of sorbitol on Cu-based catalysts for the continuous hydrogenation of CO₂-derived ethylene carbonate to methanol and ethylene glycol

The hydrogenation of ethylene carbonate (EC) is a crucial step in the indirect transformation of CO₂ into methanol (MeOH) and ethylene glycol (EG) over Cu-based catalysts. In this work, a series of sorbitol-modified Cu/SiO₂ catalyst were prepared and tested for continuous hydrogenation of EC. As a result, the MeOH selectivity displayed a volcano-like trend with the sorbitol/Cu molar ratios. The optimized Cu@0.04C_s/SiO₂ catalyst exhibited excellent MeOH selectivity (91.4 %) and EG selectivity (99.6 %) at an EC conversion of 99.9 %. The results showed that copper-sorbitol complexes were preferentially formed, which could restrict the formation of copper phyllosilicate. However, a strong electronic interaction between copper and carbon, as confirmed by multiple characterizations, which may lead to possible formation of Cu-O-C bond located on the periphery of copper and carbon interface. This interfacial effect not only reduces the activation energy but also effectively enhances the Cu⁺/(Cu⁰ + Cu⁺) ratios, and thus improves the selectivity to MeOH. Furthermore, according to DFT calculation and kinetic study results, the interface between copper and carbon serves as active sites to facilitate the adsorption of H₂ and EC, resulting in reduced activation energy.