Effect Of Heat Treatment Conditions On Catalytic Performance Of CuZnAl Catalyst For Higher Alcohol Synthesis

Higher alcohol has a very wide range of applications.It can be used as a clean liquid fuel,good gasoline additive and raw materials for the production of many chemical products.With the declining of fossil fuel resources,the research on direct synthesis of higher alcohol from syngas has attracted much attention.At present,the research on the synthesis of higher alcohol from syngas was focused on the modification of the catalyst,but the result was not satisfactory,which limited its industrial applications.In our group,CuZnAl catalyst without alkalis or F-T elements was prepared by complete liquid phased method which was proposed by ourself.It was found that the catalyst showed high selectivity of higher alcohols,especially ethanol in the CO hydrogenation reaction.But the reproducibility of the catalyst was not very good,and there was also a lack of deep understanding for the catalyst structure,so it was necessary to carry out a more in-depth study.In this paper,the effect of heat treatment temperature on the structure andIV properties of the catalyst was investigated under high pressure,and then theeffects of different CuZnAl ratios on the catalyst performance were also studied.Moreover,,the preheated liquid paraffin was used as heat treatment and reaction medium and the effect of preheated liquid paraffin on the synthesis of higher alcohol was also investigated.The catalyst was characterized by XRD,H₂-TPR,BET,NH₃-TPD-MS,XPS and SEM.Through these studies,the relationship between the structure and surface properties of the catalyst with the high selectivity of C₂₊OH was further understood.The main conclusions were as follows:1.Heat treatment under high temperature and high pressure improved the selectivity and stability for the synthesis of ethanol.When the heat treatment conditions were 4.0MPa and 280 ?,the selectivity of ethanol continued to increase with time on stream,reaching 26.13% after 120 h and remained stable.2.The catalyst with larger specific surface area,higher and stable Cu/Zn molar ratio,appropriate content of two kinds of Cu2 O and suitable proportion of weak and strong acid sites favored the improvement of ethanol selectivityand its stability.3.High-pressure heat treatment could inhibit the growth of Cu0 during reaction and strengthen the interaction between the catalyst components,thus it was easily to form a more complex spinel structure.Too much spinel would weaken the role of active components,and then decrease the catalyst activity.4.Different raw material ratio of catalysts heat treated under high pressure would affect its structure and properties.The higher content of Al element was beneficial to the formation of spinel,changing the existence of Cu2 O,reducing the pore size,making it conducive to the formation of dimethyl ether.The effect of ZnO grain size on the catalyst activity was not significant,and the increase of Zn content did not significantly promote the formation of C₂₊OH.5.Under the condition of atmospheric pressure heat treatment,the preheated liquid paraffin weakened the reduction of Cu species,improved Cu/Zn ratio on the surface of catalyst,enhanced the synergism of Cu0-Cu+,thereby the selectivity of C₂₊OH was improved efficiently.While under the condition of high pressure heat treatment,the pretreatment of liquid paraffin did not promote the formation of ethanol and C₂₊OH.