Study On CuZn-based Catalyst For The Catalytic Hydrogenation Of Co To Ethanol And Higher Alcohols

Ethanol and higher alcohols are important feedstocks for chemical industries which have wide applications in fuel and fuel additives and plasticizer.To alleviate the strong dependence on crude oil and relieve the global environmental change,the catalytic conversion of coal,biomass and natural gas into high value-added products such as ethanol and higher alcohols via the syngas route is of great value.Currently,CuZn Al catalysts prepared by the complete liquid phase method have a strong capacity for ethanol and higher alcohol generation in slurry bed reaction systems.However,we are not deep understanding the role of each component in the generation of higher alcohols due to the complexity of the catalytic system and many affecting factors.Therefore,in this paper,catalysts prepared by the complete liquid phase method were placed in a fixed bed to investigate the role of each component in the syngas conversion process.The key factors and active sites for the promotion of ethanol and higher alcohols by complete liquid phase catalysts were investigated by changing the ratios of Cu and Zn composition,the method of catalyst precursor preparation,the heat treatment and the calcination treatment of the catalyst.The reaction pathway for the synthesis of alcohols over different CuZn-based catalysts was initially explored by comparing the differences in catalyst structures and CO hydrogenation performance between commercial methanol synthesis catalyst（CMC）and the catalyst prepared by the complete liquid phase method（CZA）.The main conclusions were obtained as following:1.A series of Cu_xZn_y catalysts were prepared and applied to the CO hydrogenation reaction by changing the Cu and Zn component ratios of the catalysts.It was found that the CuZn ratio had a great influence on the reduction of Cu species,specific surface area,Cu dispersion and the amount of weak acid in the catalysts,and finally affected the performance of the CO hydrogenation reaction.With a larger proportion of Zn component,the catalyst had more reducible Cu species,a larger specific surface area,Cu dispersion and amount of weak acid,thus exhibiting the best catalytic activity.The Cu₁Zn₄ catalyst displays the highest CO conversion of 33.9%and ethanol and C₂₊OH selectivity of 35.4%and 57.6%.2.Four different CuZn bimetallic catalysts were obtained by changing the precursor preparation method and its heat treatment,and applied to the CO hydrogenation reaction.It was found that the sol-gel precursor preparation method allows for larger Cu crystallite sizes and more difficult-to-reduce Cu species,with better catalyst stability.Moreover,the catalyst structure could be further stabilized by heat treatment in an inert medium.The precursors prepared by the sol-gel method and heat treated under N₂ atmosphere were easily formed the similar structural characteristics with liquid phase thermal treatment.CAT-S-N catalyst showed better catalytic activity with a CO conversion of 10.0%and ethanol and C₂₊OH selectivity of27.3%and 43.9%,respectively.In contrast,catalyst precursors prepared by co-precipitation are methanol-dominated in the product,regardless of the heat treatment process.3.Calcinating at 300°C elicited a reduced in the carbon content of the CuZn-based catalyst surface.The results showed that the interaction between the carbon and the active component results in different levels of carbon removal,which further significantly affects the activity of CO hydrogenation reaction.The carbon species was easily removed from the bimetallic catalysts during calcination.Conversion of decarbonized CuZn bimetallic catalysts to methanol synthesis catalysts because of the interaction of Cu and Zn O.Similarly,Carbon species in monometallic Zn O catalyst was also easily removed,and Zn O can provide CO dissociation adsorption sites,increasing the potential for ethanol and higher alcohol synthesis.However,because of the strongly interacts between copper and carbon,the carbon was difficult to remove for monometallic Cu catalysts.Cu-C promotes the formation of ethanol and C₂₊OH.4.Based on the activity evaluation and characterization results,possible reaction pathways for the synthesis of alcohols over CuZn-based catalysts were proposed using in-situ DRIFTS technology.Methoxy（CH_xO*）species could be provided by both industrial methanol and complete liquid phase CuZn-based catalysts,which can be directly hydrogenated to methanol on commercial methanol synthesis CuZn-based catalysts,whereas the hydrogenation process was inhibited in the complete liquid phase CuZn-based catalysts.Surprisingly,Zn O catalyst facilitates the dissociative adsorption of CO,prompting C-O bond breaking to form alkyl（CH_x*）species,while the strong interaction between Cu and C also promote the formation of CH_x*.Finally,the CH_xO*species is coupled with the CH_x*species to form ethanol and C₂₊OH.