Effect Of Precursor Preparation Methods On Cu/Zn/Al Slurry Catalysts For Ethanol Synthesis

At present,with the increasing attention of the chinese government to environmental protection and people's growing desire for green mountains and clear waters,ethanol as an environmentally-friendly,pollution-free and reproducible energy has attracted more and more attention and unfolded promising application.China has a highly developed agriculture,but there is a large population which consumes a lot of food while it's petroleum industry is quiet dependent on imports.Thus,the synthesis of industrial ethanol which relies heavily on agriculture and petroleum industry are't conform with the china's condition.If syngas based on china's abundant coal resources as raw material to synthesize ethanol,we can not only give full play to china's energy advantages,but also reduce the ecological problems brought about by the extensive utilization of coal.Synthesis of ethanol from syngas and the accompanying side reactions are exothermic reactions.Benefit from the advantage of high thermal conductivity,the slurry bed reactor can effectively avoid the problem of deactivation of the catalyst casued by sintering during the reaction compared with the fixed bed reactor.In the early stage of research,based on the characteristics of the slurry bed reactor,our research group proposed a new catalyst preparation method??the complete liquid phase method.Based on this method,the performance of Cu/Zn/Al catalyst prepared by sol-gel method for ethanol synthesis from syngas was studied thoroughly.The research results show that the catalyst has low ethanol selectivity and poor stability,and the experimental result hard to repeat.Besides,the catalyst precursor structure is extremely sensitive,weak changes in preparation conditions will result in large performance differences.Therefore,this paper started with the preparation method of the catalyst precursor,changes the CuZn solution commonly used in the laboratory and replaces it with CuZn sol as the raw material for the preparation of the catalyst,and optimizes the preparation process.In addition,the effect of stepwise addition of AlOOH sol on the catalyst during the preparation of the catalyst was also studied.The catalysts were characterized by XRD,H₂-TPR,NH₃-TPD-MS,N₂-sorption and desorption test,FTIR,XPS and TG-DTG.The main conclusions of the study are as follows:1)The proportion of ethanol in alcohol distribution can be increased by the catalyst prepared by Al sol+CuZn sol.When the mixing temperature of Al sol and CuZn sol is 90?and the amount of citric acid is 0.05 mol,the ratio of ethanol to total alcohol is the highest.2)The Cu species which are difficult reduced and abundant weak acid sites in catalyst surface can promote the formation of ethanol;3)The addition of complexing agent can promote the dispersion of Cu species and reduce the selectivity of hydrocarbons,among which Cat-EG has the best effect;4)The grain size of Cu⁰ is a key factor affecting the performance of Cu/Zn/Al catalysts.Excessive Cu⁰ size will reduce the activity of the catalyst,resulting in higher hydrocarbon selectivity,but it is also conducive to the increase of ethanol in the alcohol distribution;5)The catalyst prepared by the stepwise addition of Al sol can increase the stability of the catalyst and significantly increase the total alcohol selectivity,but it is not conducive to catalyst activity and the increase of the ratio of ethanol to total alcohols;6)Characterization analysis found that with the increase of the amount of Al sol added in second step,the dispersion degree of Cu?Al species and the amount of Cu species which are easily reduced in the catalyst increased,the grain size of Cu decreased.