Study On The Application Of Cobalt-Based Catalysts For Selective Reductive Amination Of Ethylene Glycol

Ethylene glycol is an important platform molecule which can be used in a variety of industrial processes and has a wide range of commercial uses,such as being used as automotive antifreeze and an important monomer for synthesizng polyester polymers.In China,ethylene glycol is mainly made from coal,and the production capacity of ethylene glycol in China may be surplus in the future because of the rapid development of the coalto-ethylene glycol production process.Therefore,it is of particular importanance to convert ethylene glycol into products with high added value.Amine compounds such as ethanolamine and ethylenediamine are representative chemical substances,which are widely used in different practical fields such as chemistry,biology,medicine,energy,materials and environment.Therefore,the selective preparation of ethanolamine and ethylenediamine from the reductive amination of ethylene glycol is an effective way to enhance its utilization value and promote the sustainable development of Chinese coal-to-ethylene glycol industry.This paper focuses on the selective reductive amination reaction between ethylene glycol and NH₃ on Co-based catalysts to prepare ethanolamine and ethylenediamine,and systematically investigates the effects of support,metal loading and the doping of a second metal component on the activity and selectivity of the reductive amination reaction of ethylene glycol.The reaction mechanism of the reductive amination reaction of ethylene glycol was further explored with the aid of kinetic assessments,and the structureperformance relationship for the Co-based catalysts was unveiled.In the first part of the study,through screening different metal oxide supports（including SiO₂,γ-Al₂O₃,ZrO₂,TiO₂,MgO）,it was found that the type of support has a significant influence on the reductive amination reaction of ethylene glycol.When γ-Al₂O₃ is used as the support,the catalyst activity and ethanolamine selectivity are the highest.On this basis,the regulation of the size of metallitc Co nanoparticles was achieved by changing the metal loading,and the catalytic performance of catalysts with different Co nanoparticle sizes for the reductive amination reaction of ethylene glycol was investigated.When the Co particle size was 4.2 nm,the catalyst exhibited the highest catalytic activity and ethanolamine selectivity.Furthermore,the modification of the Co-based catalysts by metal doping such as Ag,Ru,and Cu was investigated,the results showed that the doping with Ag can significantly improve the catalytic activity without sacrificing the product selectivity.The results of H₂-temperature programmed reduction processes and scanning transmission electron microscope confirmed the exsitance of a strong interaction between Co and Ag.In the second part of the study,within the kinetic control range,the effects of ethylene glycol concentration,NH₃ pressure and H₂ pressure on the reaction rate and selectivity of the reduction amination reaction of ethylene glycol over Co/γ-Al₂O₃ and Co-Ag/γ-Al₂O₃ were investigated.With the aid of the kinetic analysis,we showed that the dehydrogenation of ethylene glycol to glycolaldehyde is the rate-determining step in the reductive amination of ethylene glycol on Co-based catalysts,and NH₃ with strong adsorption capacity is the main adsorption species on the catalyst surface.The Ag-doping did not alter the reaction mechanism of the reductive amination of ethylene glycol over the Co-based catalysts,but diluted the Co active sites,resulting in the decrease of the adsorption strength of NH₃ on the catalyst surface and thus the improvement of the catalytic activity.This effect was futher supported by the infrared characterization which showed that the Ag doping weakened the adsorption of NH₃ on the active sites of the catalyst surface.The above results on the Co-based catalysts will bring guidance for the rational design of novel catalysts for the selectivity control of reductive amination reactions of ethylene glycol and other alcohols.