Effect Of Preparation Method Of Precursor On Catalytic Performance Of CuZnAlSi Slurry Catalysts For Dme Synthesis

With the increasing energy demand and huge environmental protection pressure,dimethyl ether?DME?has received great attention as an alternative diesel fuel for its high cetane number,excellent combustion performance and low CO,NOx production.DME is widely used as chemical materials,aerosol,refrigerating fluid,foaming agent and important intermediate for other chemicals and hydrogen storage products.As one-step DME synthesis from syngas is a highly exothermic process,slurry reactor is applied for this process due to its high thermal conductivity and isothermal operating conditions.However,the catalysts prepared by traditional method have a high deactivation rate in the slurry reactor.The complete liquid phase technology developed by our group solved this hard problem.Nevertheless,the activity of the slurry catalysts still need to be improved.The preparation methods of the precursors has a significant effect on the structure and properties of the catalysts.Therefore,based on our previous studies,in order to strengthen the synergy effect between methanol synthesis and methanol dehydration component,three different solvents?ethanol,ethylene glycol and water?were used as gelling medium to prepare the bi-functional catalysts.In view of the high selectivity of CO₂,the Cu ZnAl Si catalyst was modified with Sn.The effects of Sn content and adding method on the catalytic performance was investigated.Considering crucial role of methanol synthesis reaction,three kinds of methanol synthesis functional precursors were prepared by one-stage precipitation,two-stage precipitation and fractional precipitation to investigate the catalytic properties.XRD,H₂-TPR,NH₃-TPD-MS,N₂-adsorption,XPS and TEM were used to explore the relationship between structure and catalytic performance.The main conclusions are as follows:1.Using different solvents as dispersion medium of Cu ZnAl precipitate and dehydration components to form sol-gel could significantly affect Cu0 particle size,surface acid amount and acidity,relative proportion of surface elements and control the concentrations of reducible Cu species,which were the main reason for the differences of catalytic performances.The catalysts using ethanol as dispersion medium performed the best catalytic activity.2.The addition of Sn could obviously enhance the selectivity of DME.Sn could promote the formation of small Cu particles,which was beneficial to improve the catalytic activity.The enrichment of Sn on the surface was unfavorable to the CO conversion and selectivity of DME.The optimal content of Sn was Sn:Al=11:900?molar ratio?.Adding Sn at the end of co-precipitation,and aged 2 h with the CuZnAl precipitate together in the mother solution was the optimal way.The average CO conversion and DME selectivity within 120 h of the catalyst with the above two conditions were 53.47% and 82.12% respectively.3.Different preparation methods of methanol precursors could significantly affect the structure of the catalysts.The catalyst prepared by fractional precipitation method possessed the strong interaction between Cu and Zn,small Cu particles,large BET surface area and more reducible species,leading to the best CO conversion and selectivity of DME.