Influence Of Support Structure On Stability Of Copper-based Catalyst For Catalytic Hydrogenation Of Dimethyl Oxalate To Ethylene Glycol

Ethylene glycol（EG）is an important basic chemical raw material,which is widely used in polyester,pharmaceutical and fragrance fields.At present,our country has a large demand for EG,and the production capacity of EG is far from the market demand.Combined with the energy structure in our country,dimethyl oxalate（DMO）is obtained by oxidative coupling of coal-based syngas,and then DMO is catalytically hydrogenated to EG.Thise C1 synthetic route has the advantages of abundant raw materials,environmentally friendly and mild reaction conditions.This not only has important strategic significance for adjusting our country’s energy structure,but also provides favorable conditions for the industrial production of EG.The preparation of efficient and stable catalyst for the catalytic hydrogenation of DMO to EG is the key to this route.At present,the DMO hydrogenation catalyst still has the problem of insufficient stability,which largely hinders the industrial production of EG.Therefore,it is particularly important to develop efficient and stable catalysts for the hydrogenation of DMO to EG.In this thesis,to improve the activity and stability of copper-based catalysts for hydrogenation of DMO to EG,mesoporous silica supports with different structures and morphologies were prepared by different means.On this basis,the support structure was further optimized by changing the hydrolysis temperature of the support raw materials and the conductivity of the medium water.XRD,BET,SEM,TEM,H₂-TPR,FT-IR,ICP and XPS were used to establish the relationship between the support structure and the physicochemical properties and catalytic performance of the catalyst.The main conclusions of this study are as follows:（1）The MS-3 support prepared by room temperature agitation with large specific surface area,particle size and ordered pore structure was not only beneficial to disperse and confine copper nanoparticles,but also conducive to the formation of copper phyllosilicate phase.The copper phyllosilicate could provide a large amount of stable Cu⁺species and make the copper species closely contact with the MS-3 support.The enhanced metal-support interaction and more stable Cu⁺species endowed the Cu/MS-3 catalyst with excellent DMO catalytic hydrogenation activity and stability.Among them,DMO was completely converted,the EG selectivity was 97.9%,and the stability could reach more than 400 h.（2）By changing the hydrolysis temperature of the support raw material,the structure of support was adjusted to explore the influence of the hydrolysis temperature on the structure of support and the catalytic hydrogenation performance of the supported copper catalyst.It was found that the specific surface area and particle size of the support decreased with increasing the hydrolysis temperature of support raw material,which had significant effects on the structure and catalytic performance of the catalyst.The reaction evaluation results showed that the specific surface area and particle size of the support decreased,the stability of Cu/MS-x catalyst decreased significantly.Among them,the stability of Cu/MS-30 and Cu/MS-35catalysts were 279 h and 276 h,respectively,which was much lower than that of Cu/MS-25catalyst（>400 h）.With the decrease of specific surface area and particle size of the support,the dispersion of copper particles in the catalyst became deteriorate and reduces the proportion of Cu⁺decreased,which was not conducive to improving the stability of the catalyst.（3）The lower the conductivity of medium water,the better the long-range order of pore structure of the prepared support.The highly ordered pore structure was conducive to the dispersion of active metals,increase the proportion of Cu⁺species,and then improve the catalytic stability of the catalyst.The Cu/MS-P catalyst exhibited excellent catalytic activity and stability.At a lower temperature of 168°C,DMO conversion was 99.4%,EG selectivitywas up to 98.9%,1,2-BDO selectivity was less than 0.3%and the stability was over 487 h.（4）The structure and stability of catalysts were not completely affected by single structural parameters of the support,but by the interaction of various structural parameters（specific surface area,particle size and order）.The particle size and order of the support had the greatest influence on the structure and stability of the catalyst.