Co-Mn Catalysts Via Hydrotalcite-like Precursors For CO Hydrogenation To Higher Alcohols

With the depletion of fossil fuels and the increasing pollution of the environment,the development of new energy and evolution of traditional energy technologies is an inevitable trend.Mixed alcohols can be used as clean fuels,fuel additives,and many important chemical products.Therefore,the wide source of syngas convert to higher alcohols（HAS）has far-reaching significance.Among syngas conversion of various technologies,methanol synthesis,FT synthesis has achieved industrial applications,while the synthesis of mixed alcohol technology has not yet achieved industrialization owing to the shortcoming of catalyst selectivity and stability constraints.Therefore,the development of new and efficient catalyst for the synthesis of mixed alcohol become an important issue.The requirement of catalyst for the formation of mixed alcohols is that it has both dissociation activity of CO to achieve chain growth,but also has non-dissociation activity to achieve the formation of alcohol.In the mixed alcohol catalytic system,cobalt-based catalyst developed more mature,but only if add the appropriate additives can improve the selectivity of alcohol products.The study found that the addition of Mn can improve the yield and selectivity of higher alcohols.In addition,the nature of the precursor also affects the structure and properties of the catalyst.The hydrotalcite-like compound is a new type of material with a layered structure.The catalyst derived from the hydrotalcite precursor obtain a high specific surface area,high thermal stability and improve the interaction of active components.It is a promissing way to improve the catalyst activity and alcohol selectivity,and stability,so as to gain a new and efficient mixed alcohol catalyst research foundation.In this paper,the structure and physicochemical properties of the catalysts were studied by XRD,ICP,N₂ adsorption,TPR,SEM,TG,TEM,XPS,and Mapping.The catalytic performance of the catalysts was also studied and compared with the non-layered structure catalyst,the main contents and results are as follows:（1）Compared with the structure and properties of CoMn catalyst prepared by hydrotalcite precursors and non-hydrotalcite precursors,it was found that the hydrotalcite precursors could keep the catalyst larger specific surface area after reduction,and gain smller particles.What’s more the CoMn is highly dispersed,and the interaction between CoMn is enhanced.In addition,according to the results of TEM,XPS,Mapping and so on,it can be seen that the layered structure of hydrotalcite precursors can effectively prevent the catalyst agglomeration,so that the CoMn catalyst derived from the hydrotalcite-like precursor has higher activity and selectivity under high reaction temperatures.（2）The effects of different Co/Mn ratios on the structure and properties of CoMn hydrotalcite-like catalysts were studied.The results showed that when the Co/Mn ratio was 2,the specific surface area was the largest and the reduction performance was the best,and provide more regular layer structure so that prevent the agglomeration.In addittion,when theCo/Mn ratio is 2,it can provide a suitable Co and Co₂C ratio,so that the activity and alcohol selectivity are the best.（3）The catalytic performance of the CoMn hydrotalcite-like catalyst at different reduction temperatures,H₂/CO ratio in feed gas and airspace velocity of feedgas were investigated.The results showed that the CO conversion was higher after reducing at 200℃,but the selectivity of higher alcohols is lower.The selectivity of C₆₊alcohols is higher and the alkene ratio is higher when the reduction temperature is 300℃.When the reduction temperature is 400℃,the content of Co increased and the CO conversion is obvious higher,while the selectivity of alcohol was significantly decreased,indicating that the interaction between Co and Mn could improve the CO conversion.With the increase of H₂/CO ratio in the feed gas,the conversion of H₂ decreased while the CO conversion increased,but the alcohol selectivity and the yield of alcohol decrease,while the selectivity of hydrocarbons increased,indicating that the high H₂/CO ratio in the feedgas was favorable for the hydrogenation reaction,and the chain growth reaction of the alcohols was inhibited but promote the chain growth reaction of the hydrocarbons.Under the conditions of different airspace velocity,When the space velocity is less than 6000 h^-1,the conversion of H₂ and CO decreases with the increase of airspeed,the selectivity of alcohol and the yield of alcohol increase,and the higher alcohol ratio increases,while hydrocarbon and CO₂ selectivity decreased.In addition,the product alkene ratio increase with increasing airspeed.The stability of the catalyst was also investigated.It was found that the CoMn catalyst derived from the hydrotalcite precursor keep stable on the activity and the selectivity of higher alcohol during the 252 h reaction time,indicating that the CoMn catalyst prepared by the hydrotalcite-like precursors had great stability.