Study On The Modification And Deactivation Mechanism Of Cu-based Catalyst For Hydrogenation Of Methyl Glycolate

In recent years,the successful development of the process of dimethyl oxalate（DMO）hydrogenation to ethylene glycol has laid a solid foundation for preparing ethylene glycol through non-petroleum route in China.Cu-based catalysts show superior activity and selectivity in the hydrogenation of DMO,thus drawing wide attention.At present,the stability of copper-based catalyst in DMO hydrogenation has been a bottleneck problem.The lack of researches on deactivation mechanism makes it difficult to design and prepare high stability catalysts.In this paper,we concentrate on the deactivation mechanism of copper-based catalyst in DMO hydrogenation and adopt the appropriate strategy to preparet high stability catalyst according to the deactivatio n mechanism.In this work,we found that when the residence time of reactants was regulated so that the main DMO hydrogenation product DMO was methyl glycolate（MG）instead of ethylene glycol,the Cu/SiO₂ catalyst was more inclined to deactivate.Therefore,in this paper,we chose MG hydrogenation as the model reaction to investigate the deactivation mechanism of Cu/SiO₂ catalyst prepared by ammonia evaporation method The results showed that carrier loss in the form of tetramethoxy silane（TMOS）damaged the physical structure of the catalyst.In addition,the agglomeration of copper nanoparticles was also not the main factor for the catalyst deactivation.Through characterization of GC-MS and LC-MS for catalysts with different deactivation degrees in the MG hydrogenation we found that the surface of the catalysts was covered with plenty of organic macromolecular substances,such as long-chain alkanes and oligo mers containing benzene rings.Combined with the characterization results,such as XRD,NH₃-TPD and CO₂-TPD,we speculated that the acidic and basic sites on the catalyst surface lead to hydroxyl dehydration,condensation,aromatization and other side reactions of MG.Macromolecules formed by condensation polymerization reaction cover the surface of the catalyst and block the pore channel,resulting in rapid deactivation of the catalyst.The discovery of the deactivation mechanism will provide significant guideline for the development of highly stable copper-based catalysts for DMO hydrogenation.Based on the established deactivation mechanism,we could introduce dopants Ni and La into Cu/SiO₂ catalyst to improve its stability in MG hydrogenation.Above.We found that the addition of La endowed the catalyst with more basic sites on the surface suppressing the side reaction of carbon deposition.And doping of Ni prompted the reduction of surface copper species in the catalyst and tuned the acidic and basic properties on the catalyst surface,improving the activity and stability of catalyst in MG hydrogenation.These findings provide important theoretical basis for the design and preparation of high stability catalyst for dimethyl oxalate hydrogenation to ethylene glycol.