High Stable Copper-based Catalysts For Ethylene Glycol Synthesis From Hydrogenation Of Dimethy Oxalate

Ethylene glycol（EG）is an important organic material and product with wide application and considerable market potential.The production of EG from“coal–DMO–EG”process has attracted increased attention and rapid development in China in the last two decades.However,one of the key challenges is to find a suitable catalyst for the hydrogenation of DMO to EG.It is general that the copper based catalysts are easy to aggregate and grow,and difficult to operate in DMO hydrogenation reaction for a long time.To solve this problem,there are several issues have been considered,such as improving the dispersion of copper in catalyst,adding promoter to enhance the stability and reasonable adjusting the proportion of Cu/Cu⁺of the catalyst,and the nanometer size effect of the carrier is also considered.In order to improve the stability of the catalyst,the following methods are adopted in this study,such as preparation of catalyst by plasma and magnetron sputtering,doping the promoter of titanium,tin and palladium in catalyst,and using different nano-sized silica sol as supports to prepare catalysts,The results are as follows:1.The copper dispersion and stability of Cu-Ni/ZrO₂ catalyst after plasma treatment were improved effectively.The argon plasma pretreated catalyst was used for hydrogenation of DMO,the conversion of DMO was about 100%,the selectivity of EG≥96%,and the life span increased to more than 150h.Furthermore,it was found that the catalytic performance of Cu-Ni/SiO₂ by hydrogen plasma pretreatment was better than that of conventional heating and reducing catalyst.The results showed that the particle size of copper on the surface of the catalyst was reduced after the plasma treatment,and more copper exposed on the surface of the catalysts.Which results in the improvement of catalytic performance.2.M-Cu/SiO₂ catalysts were prepared by magnetron sputtering with additives doping.The results show that Ti,Ni and La can promote the catalyst.It was found that the catalytic performance of Ti-Cu/SiO₂ was the best when the sputtering time was 60min.It may be because of the presence of Ti₂O₃,which enhances the binding force to copper.3.The addition of Sn²⁺to Cu/SiO₂ catalyst caused a significant change in the catalytic performance of DMO hydrogenation.The catalyst has the best performance when the tin doping amount was 0.6%in the catalyst,the conversion rate was 100%,the selectivity of EG was more than 96%,still did not drop after 200 hours of reaction.It is possible that Sn²⁺doping adjusted the Cu⁰/Cu⁺ratio and prevented copper migration of aggregation.4.Palladium doped Cu/SiO₂ catalyst not only enhanced the thermal stability,but also improved catalytic activity and life span.The optimal catalyst was Cu-0.5%Pd/SiO₂,the conversion of DMO was about 100%,the selectivity of EG was more than 95%,it did not decrease after 300 hours of reaction.Which attributed to the hydrogen overflow generated by palladium,the increasing of local H concentration and the formation of Cu-Pd alloy.5.The Cu/SiO₂ catalysts were prepared by using different nano sized silica sol as the supports.The results showed that the catalytic performance and stability of the catalysts were Cu/4–SiO₂﹤Cu/20–SiO₂﹤Cu/10–SiO₂.The DMO conversion rate of Cu/10-SiO₂ was 100%,the selectivity of EG was more than 94%,the life span was over 3080h when WLHSV was 0.5h^-1.This is due to the small particle size and large specific surface area of Cu/10–SiO₂ catalyst,which can effectively prevent the migration of copper.