Catalytic Role Of Lewis Acid Of Supported Metal Catalysts In The Reaction Of Ethanol To Butanol

In order to alleviate human consumption of non-renewable energy,renewable clean energy has been gradually developed and utilized.For example,bioethanol and butanol can be used as gasoline additives.Because butanol has more suitable properties than ethanol,and comparing with the traditional industrial route for butanol production by fermentation or carboxyl synthesis,the catalytic route of ethanol to butanol is more consistent with the concept of green sustainable development,thus is receiving wide attention from both homogeneous and heterogeneous catalysis.At present,although heterogeneous catalytic systems have some obvious advantages over homogeneous catalytic systems,they also give rise to low selectivity to butanol,due to the complex of the ethanol-to-butanol reaction network.The effect of the type,amount and strength of some catalytically active sites on the reactivity and selectivity is still not clear.Therefore,when designing catalysts,it is often difficult to accurately construct active sites that can effectively catalyze the conversion of ethanol to butanol.Recently,our research team found that there are two main problems need to be solved:?1?Copper-based catalysts have good catalytic potential,but often accompanied by the production of a large amount of ethyl acetate,limiting their selectivity towards butanol.Moreover,there has been controversy over the active sites for ethyl acetate.?2?The unsaturated Zr cations in MOF catalysts were used as Lewis acid sites and showed excellent aldol condensation activity,however,the relationship between the activity of aldol condensation and the properties of Lewis acid sites has not been elucidated.In view of the above two problems,this paper mainly focuses on the structure-activity relationship between the catalyst properties and catalytic performance.A series of activated carbon-supported Cu-Ce O₂ catalysts?G_x-Cu Ce O₂/AC,G stands for glucose and x is the molar ratio of glucose to metal?,in which glucose was used to regulate the interaction between Cu and Ce O₂,were first prepared.Then,the catalytic activity of the G_x-Cu Ce O₂/AC catalysts was evaluated and characterized by XRD,H₂-TPR,TEM,NH₃-TPD,XPS and N₂O titration.When analyzing the structure-activity relationship between Cu species?Cu⁰ and Cu⁺with Lewis acidity?and catalytic performance,it was found that both Cu⁰ and Cu⁺are involved in the formation of ethyl acetate,and the ratio of S_Cu⁰/S_Cu⁺ can be used as an indicator of catalytic performance.The higher the ratio of S_Cu⁰/S_Cu⁺,the higher the selectivity of ethanol to butanol,and the lower the selectivity to ethyl acetate.In contrast,the lower the ratio,the more ethyl acetate is produced.In addition,MIL-101?Cr?was used as a support,and Pd/MIL-101?Cr?catalysts ware prepared to investigate the effect of the properties of Lewis acid sites of the support on the atalytic performance of ethanol to butanol.Because MIL-101?Cr?mainly has Lewis acid centers,and the amount of Lewis base and Br?nsted acid is almost negligible.By adjusting the synthesis conditions of of MIL-101?Cr?crystals,three MIL-101?Cr?supports with different coordination environments can be obtained,leading to changes in the acidity of the supports.We further clarified that the main difference in the properties of these three supports is Lewis acidity by using SEM,TG-MS,CO₂-TPD,and NH₃-TPD.Then they were used to prepare Pd/MIL-101?Cr?catalysts and catalytic activity was tested.The catalysts were subsequently characterized by XRD,TEM,FT-IR,and IR spectroscopy of pyridine adsorption.When analyzing the activity data and characterization results,it was found that the strength of the Lewis acid sites does not correlate with its activity.If there is only one strong Lewis acid in the reaction of ethanol to butanol,it will cause a sharp increase in the formation of ether and thus affect the aldol condensation.Whereas,when combining with some weak Lewis acids,it will benefit the conversion of ethanol to butanol.