The Study Of Preparation Of Cu-Zn-Al Catalyst By Solvothermal Method And Its Catalytic Performance For Ethanol Synthesis From Syngas

As a low consumption,high efficiency and well-stocked supply of raw materials of synthetic route,catalytic conversion of syngas to ethanol and higher alcohols has attracted a great deal of attention of scholars both at home and abroad.Cu-Zn-Al catalysts were prepared by the complete liquid-phase technology which our group research domestically developed and were used for CO hydrogenation reaction in a slurry bed reactor.In the research,we find that the catalyst prepared by complete-liquid-solvothermal technology has higher ethanol selectivity,but its activity,repeatability and stability are poor.Therefore,in this paper,we prepared the Cu-Zn-Al catalysts by solvothermal method and the catalysts for ethanol synthesis were evaluated in a slurry bed reactor and characterized by NH₃-TPD-MS,XRD,SEM,H2-TPR,XPS,N₂ adsorption.We inspected the effect of precursor preparing conditions,heat treatment conditions and reduction conditions on the structure and performance of the Cu-Zn-Al catalysts.According to the activity data and characterization results,we get the following conclusions:Cu-Zn-Al catalysts prepared by solvothermal method have the ability to chain growth and can catalyze CO hydrogenation to ethanol.The highest ethanol selectivity reached 38.71%,but the CO conversion and stability were poor.On the whole,there are one problem is that the balance of CO conversion and ethanol selectivity could not obtained at the same time.In the precursor preparation,the exposure time and Al content had significant influence on the CO conversion and the ethanol selectivity.Prolonging the exposure time made the Cu+ difficult to reduce,and made the the oxidation state of Cu species more complex,which improved the CO conversion and the initial ethanol selectivity.Increase of Al content in catalysts could improve the specific surface area of the catalysts and promote the formation of the CuAl2O4/ZnAl2O4 spinel phase,but the latter was not conducive to the catalyst activity.When the molar ratio of raw materials was 2:1:0.8,the Cu-Zn-Al catalyst had the highest ethanol selectivity.The characterization results showed that the catalyst contained more Cu+ difficult to reduce,the smaller grain size of Cu and the larger pore volume,the ethanol selectivity was higher.The stirring intensity,time and self-generated pressure of heat treatment had great influence on the structure and catalytic performance of the Cu-Zn-Al catalyst prepared by solvothermal method.The results showed:?1?The heat-treatment environment without stirring was more conducive to the dispersion of Cu and the stability of the catalyst structure;?2?With the heat treatment time extended,the phase of the catalysts and their crystallinity gradually changed,and the weak acid content on the catalyst surface decreased and the acid strength gradually increased;?3?The higher autogenous pressure was more favorable for the reduction of Cu species.In a nutshell,when the heat treatment temperature is 200?,the heat treatment time is 24 h and under the stewing condition,the CO conversion and ethanol selectivity of Cu-Zn-Al catalyst are higher.The effect of temperature and atmosphere of reduction were studied over Cu-Zn-Al catalyst prepared by solvothermal method.The results showed that when the reduction temperature was 250? and the reduction atmosphere was N₂+H2,the CO conversion and ethanol selectivity were better.Under these conditions,the interaction between the components in the catalyst changed smaller,the catalyst structure more stable,the ethanol selectivity is higher.This study used the autoclave to heat precursor,the weak acid slurry caused the corrosion of the high pressure reactor,and thus resulting the Fe phase in the Cu-Zn-Al catalyst.The presence of Fe reduced the dispersion of Cu,consequently reduce the activity of Cu-Zn-Al catalyst,but the presence of Fe markedly improved the ability of the catalyst to produce ethanol.