Preparation Of Cu/SiO₂ Catalyst And Study On DMO Hydrogenation Performance

Methyl glycolate（MG）,with both hydroxy and ester functional groups,is considered as an important chemical intermediate that possesses wide applications in medical and chemical fields.At present,there are some problems during the preparation of MG,such as serious pollution,strong corrosion to equipment and low yield.As a new environment-friendly process,the selective hydrogenation of dimethyl oxalate（DMO）,which has high atom utilization rate and no secondary pollution,can not only effectively promote the harmonious development between environment and economy but also meet the requirements of development of green energy in China.For the hydrogenation of DMO to MG,it is critical to design and synthesize catalysts with excellent catalytic activity.Due to low cost,high activity for the hydrogenation of the C-O/C=O bond and low activity for hydronolysis of the C-C bond,copper-based catalysts have been widely used in the hydrogenation of esters.Generally,Cu⁺/Cu⁰ is considered to be the active center for ester hydrogenation.Cu⁰ promotes the dissociation of H₂,while Cu⁺promotes the dissociation of DMO molecules and stabilization of acyl species,and an increase content of Cu+sites facilitates to improve MG selectivity.It is found that the catalytic performance of copper catalysts is mainly affected by supports,preparation methods and additives.Si O₂ has been considered as an excellent support because of its controllable morphology,high thermal stability and chemical stability.In addition,the interaction between Si O₂ and copper can effectively regulate both dispersion and the valence distribution of copper species.In this work,the Cu/Si O2 is prepared form layered copper silicate catalyst by the improved sol-gel one-step method.The preparation conditions were optimized.The effects of calcination temperature and silver promoter on the texture properties of catalyst,the dispersion of copper and the chemical state of copper species were systematically investigated.Furthermore,the structure activity relationship of Cu/Si O₂catalyst in the hydrogenation of DMO to MG was further explored.The mechanism of silver（Ag）promoter on the performance of Cu catalyst was also discussed.The main research contents are as follows:1.Cu/Si O₂ catalyst was prepared by gel-sol one-step method,and its calcination temperature was optimized.When the calcination temperature was 500°C,the content of layered copper silicate was the highest.With the further increase of calcination temperature,the content of layered copper silicate decreased.2.The content of Cu⁺on the reduced catalyst surface was correlated with the content of layered copper silicate,and achieved the maximum in Cu/Si O₂-500 catalyst,which exhibited the optimal catalytic activity with DMO conversion of 98.5%and the MG selectivity of 51.1%.3.The Ag promoter was introduced to improve the catalytic performance of Cu/Si O₂catalyst.The results showed that when the loading amount of Ag was 5 wt%,the DMO conversion and MG selectivity achieved the optimal values of 83.7%and 72.2%,respectively.4.The introduction of appropriate amount of Ag not only improved the dispersion of copper species,but also increased the content of Cu⁺on the surface of the catalyst.In addition,the silver promoter also enlarged the mesoporous pore size in the catalyst,which promoted the diffusion of DMO and MG molecules,thus improving the catalytic activity.5.Compared with the Cu/Si O₂ catalyst,the 5Ag-Cu/Si O₂ catalyst showed better stability,which may be attributed to the electron transport between Ag and Cu and the physical barrier effect of silver,which contributed to the stabilization of Cu⁺and immobilization of Cu nanoparticles.