The Study On Preparation Basis Of CuZnAl Catalysts For Higher Alcohols Synthesis From Syngas

Higher alcohols,whose carbon numbers are between one and six,can be used as clean liquid fuel,fuel additives,and other feed stock or intermediates such as medicine,cosmetic.Our country has been facing with the energy status that coal reserves are rich while oil and natural gas resources are scarce.And the route of methanol production from coal-based syngas had been applied in industrial circle.The study on synthesis of C₂₊OH from syngas is becoming a fascinating subject in recent years.The catalysts used for the synthesis of higher alcohols from syngas exists some issues such as high costs,harsh reaction conditions,excessive methanol in resultants.So it is the objectives for researchers to develop catalysts with excellent performance and low costs.CuZnAl catalysts had been used for the production of methanol in industry and generally prepared by precipitation methods.In the preparation of slurry CuZnAl catalysts,our group independently developed complete liquid phase method.The research results show that the slight differences on the structure of catalysts will bring about big differences on the selectivity of C₂₊OH.In the preparation of catalysts,the structure of catalysts are closely connected to the characteristic of catalyst precusors.We prepared catalyst precursors by sol-gel methods and started with“raw material→sol→gel”.Firstly,we studied the effects of solvents in the preparation of aluminum sol and pressure in the heat treatment on the performance of catalysts;Secondly,on the basis of it,we explored the influences of the type and amount of organic acid complexing agents on the structure and performance of catalysts;Finally,we studied the effects of hydrolysis environment of aluminum isopropoxide（AIP）on the structure of precursors and the performance of catalysts.The performance of CO hydrogenation for catalysts was examized in the slurry bed,and the properties of catalysts were characterized by XRD、NH₃-TPD-MS、H₂-TPR、FT-IR、TG-DTG、XPS、N₂-sorption and desorption.By these ways,we explored the relationships between structure and performance of catalysts.And the main conclusions were drawn by item:1.Aluminium sol was prepared with different solvents would affect the ability for Cu species to be reduced and the dispersity of active species.When chose water as solvent,the crystallite sizes of Cu⁰ were smaller and reducible Cu species were more on catalysts;when chose ethanol or isopropanol as solvent,the crystallite sizes of Cu⁰ were bigger and more stable.While the conversion of CO and the ratio of C₂₊OH in total alcohols were both lower.2.The heat treatment pressure of precusors had directly influences on the specific surface area and the dispersity of active species.The catalysts prepared by high pressure had smaller specific surface area,bigger Cu⁰crystallite sizes,and the production ability in C₂₊OH were slightly better,while the stability were worse.3.Oxalic acid,tartaric acid or citric acid was chosen as complexing agent,and the acidic property of organic acids had positive relations with the crystallite sizes of Cu⁰ under same amount.The catalyst was prepared with citric acid would have less surface amount of acids and smaller crystallite sizes of Cu⁰.While the surface amount of acids and crystallite sizes of Cu⁰ had an increasing tendency with the increasing amount of citric acid.4.The feeding sequences could directly affect the hydrolytic environments of aluminum isopropoxide,and then affect the polyesterification of precusors which was closely related to the contents of Cu⁺and the surface n（Cu）/n（Zn）.5.The catalyst prepared by hydrolyzing of aluminum isopropoxide in citric acid aqueous solution had bigger crystallite sizes of Cu⁰,suitable amount of weak acids and higher n（Cu+Zn）/n（Al）on the catalyst surface,and presented certainly ability to produce C₂₊OH.The catalyst prepared by the glycolysis of aluminum isopropoxide in ethylene glycol had abundant weak acid sites,higher surface Cu content and presented better catalytic activity.6.In the research system of this paper,it was beneficial for the formation of C₂₊OH when the reaction temperature was 250℃,while 280℃could improve the selectivity of dimethyl ether and hydrocarbon,and it had positive relations between dimethyl ether and higher alcohols in selectivity.