Research And Development Of Ag/ZrO₂ Composite Catalyst For Hydrogenation Of Dimethyl Oxalate To Methyl Glycolate

Methyl glycolate（MG）is an important intermediate for the synthesis of pharmaceuticals and dyestuffs,and it has a wide range of applications.At present,there are many methods for the synthesis of MG,among which the synthesis gas generates dimethyl oxalate（DMO）,and then further hydrogenation to MG has the characteristics of wide source of raw materials and no pollution,which meets the requirements of green development in China.At present,Cu-based catalysts are commonly used for DMO hydrogenation,but due to the excessive hydrogenation capacity of Cu-based catalysts,they are often used for the preparation of ethylene glycol.However,MG,as an intermediate product of DMO hydrogenation,is likely to cause the reduction of MG selectivity because of excessive hydrogenation,so it is very important to control the degree of hydrogenation of catalysts.Ag-based catalysts are widely used for DMO hydrogenation to MG due to their relatively weak capacity of hydrogenation.In this thesis,the silver is selected as the active component,and the catalytic activity of catalysts was enhanced by the addition of additive metal and modification of the carrier,by the way,it can improve the yield of MG.And the author designed catalysts about DMO hydrogenation to MG,including Ag-Cu/ZrO₂、Ag-Ce/ZrO₂、Ag/ZrO₂-SiO₂,and discussed the effects of the content of active component,the content of auxiliary metal,the content of SiO₂in the carrier and reaction conditions.The studies are as follows:（1）Application of Ag-Cu_X/ZrO₂ catalyst in DMO hydrogenation to MGAg-Cu_X/ZrO₂ catalysts with different copper contents were prepared by impregnating,and the effects of catalysts on the reaction of DMO hydrogenation to MG were investigated.It shows that addition of copper affects the catalysts of density of oxygen vacancies and the electron cloud density around the silver.The synergy of Cu⁺and Cu⁰by CuO reduction,which can improve the hydrogenation activity of the catalysts.And when the content of the auxiliary metal copper is 3 wt%,the conversion of DMO is 88.70%,the selectivity of MG is 83.10%,and the yield of MG is 73.71%.（2）Application of Ag-Ce_X/ZrO₂ catalyst in DMO hydrogenation to MGDifferent Ag-Ce_X/ZrO₂ catalysts were prepared by impregnation,and the author discussed the effect of the different contents of cerium on the reaction of DMO hydrogenation to MG.The results show that it’s beneficial for the catalyst with addition of metal cerium to form more oxygen vacancies and change the electron cloud density around the silver,which makes Ag₂O more easily reduced to silver.Compared with Ag/ZrO₂ catalyst,the MG yield of Ag-Ce/ZrO₂ catalyst is improved,and the DMO conversion of Ag-Ce₁/ZrO₂ catalyst is 94.29%and the MG selectivity is 85.8%,and the MG yield is 80.88%.（3）Application of Ag/ZrO₂-SiO₂ catalyst in DMO hydrogenation to MGAg/ZrO₂-SiO₂ catalysts were synthesized by the hydrolysis-impregnation and applied to the DMO hydrogenation to MG reaction.A series of characterizations were used to characterize the catalysts after roasting and reduction.The catalytic test and characterization results showed that the introduction of SiO₂can increase the number of acid sites and oxygen vacancies in the catalyst,enhance the interaction between silver and the carrier,and reduce the size of particles of silver.Compared with the Ag/ZrO₂ catalyst,the addition of SiO₂ achieved high activity of the catalyst under low pressure conditions.Among them,the Ag/4ZrO₂-3SiO₂ catalyst had the highest catalytic activity with 96.00%conversion of DMO,92.40%selectivity of MG and 88.90%yield of MG,at 0.5 MPa.