Study On Cu/SiO₂ Catalyst Of Dimethyl Oxalate Hydrogenation To Ethylene Glycol Modification

The synthesis process of ethylene glycol(EG) from synthesis gas is the most promising synthetic route for industrial application, due to its simple process, low energy consumption and relatively high selectivity of EG, which includes oxidative coupling reaction of carbon monoxide to dialkyl oxalate, and the catalytic hydrogenation of dialkyl oxalate to ethylene glycol. However, the Cu/SiO2 catalyst of ethylene glycol from dimethyl oxalate hydrogenation is sensitive to reaction temperature which leads to side reactions in high reaction temperature, and the catalyst has poor stability. In this paper, the performance of Cu/SiO2 catalyst was modified by different precipitators and promoters, bulk structure,reducibility,acidity and basicity of catalysts's surface and their effects on the catalytic performance were studied by XRD,BET,H2-TPR,CO2/NH3-TPD. The main contents of this paper are as follows:Firstly, Cu/SiO2 catalysts with 30wt% of Cu were prepared with different precipitators and methods. Under certain conditions, the effects of precipitators,precipitation methods,potassium and sodium ions were investigated, the results showed that the Cu/SiO2 catalysts prepared by homogeneous deposition-precipitation methods with urea as precipitator had better catalytic performance with high catalytic activity and selectivity of EG, therefore, Cu/SiO2 catalyst with urea as precipitator had the value of research and development; For different precipitators, the precipitation methods had different effects on Cu/SiO2 catalysts'performance, precipitation method should be chosen, according to different precipitators; Compared with potassium ion, sodium ion was more easily to be washed, but a small amount of sodium ion would inhibit the further hydrogenation of MG and reduce the selectivity of EG.Secondly, the results of catalysts evaluation showed that adding Al,Zn,Mg and Ca promoters restained the activity of Cu/SiO2 in different degrees. Though adding 3wt% of Mg promoter decreased the activity of Cu/SiO2 catalyst slighly, it can keep the selectivity of MG in high value in larger temperature range, therefor a high activity catalyst of dimethyl oxalate hydrogenation to methyl glycollate can be developed.Lastly, it's found that the ratio of acid sites concentration and basic sites concentration of Cu/SiO2 catalyst was 3.09 by CO2-TPD and NH3-TPD, which showed the Cu/SiO2 catalyst was acidic, however, adding four promoters decreased the acidity, the order was Mg>Zn>Al>Ca. Besides, it's found that four promoters reduced the reducibility, made the catalysts difficult to be reduced.