Modification Of Cu/SiO₂ Catalysts Using Silane Coupling Agents For Hydrogenation Of Dimethyl Oxalate To Ethylene Glycol

Ethylene glycol（EG）,as an important raw material for synthesizing polyester fibers,becomes a promising product in the global market.Based on the fossil energy reserves distribution in China,conversion of coal to EG meets the major development strategy.The technology of producing EG from syngas via dimethyl oxalate（DMO）hydrogenation has been widely applied with increasing trend in China.However,there are some aspects of the catalyst for DMO hydrogenation still needed to be improved,such as the selectivity of EG and long-term stability.Herein,we used a series of silane coupling agents to modify the surface of Cu/SiO₂ catalysts by the post-grafting method,and investigate its effects on selectivity and stability.We also changed the amounts and kinds of the functional groups to explore their catalytic behavior in DMO hydrogenation,which may provide experimental and practical guidance for further design of Cu/SiO₂ catalysts for industrial application.By using post-grafting method to modify Cu/SiO₂ catalysts with silane coupling agents,amino and alkyl groups were successfully introduced along with stable coverage of hydroxyl groups on the support surface.The catalysts after modification showed excellent selectivity of EG and stability in DMO hydrogenation.Given the experimental results,the density and intensity of surface basic sites on the modified catalysts were remarkably decreased,leading to the reduced by-products selectivity of C3-C4OH,among which the alkyl modified catalyst exhibited the optimal selectivity of EG due to the weakest surface basicity.Additionally,the modified catalysts could effectively facilitate MG desorption and prevent excessive MG absorption and polymerization on the surface,resulting in a remarkably promoted stability,especially for the amino modified catalyst.By adjusting the amounts and kinds of amino group in the silane coupling agents,the coverage of hydroxyl groups and nitrogen contents of the modified catalysts could be easily controlled.In spite of the introduction of amino groups accompanied with medium strong basic sites,the density and intensity of the surface basic sites decreased notably after modification,which reduced the formation of C3-C4OH by-products.Furthermore,the catalysts modified with amino groups exhibited significantly enhanced activity in DMO hydrogenation.It could be deduced that the amino could act as electron-donating groups and consequently increase the ratio of Cu⁰ species,accelerating the dissociation of H2.Meanwhile,its medium strong basic sites may be in favor of the adsorption and activation of the DMO molecular,thus greatly increasing the activity of DMO hydrogenation.The understandings may provide guidance in further design of industrial catalysts.