Study On Structural Construction And Reaction Mechanism Of Catalyst For CO₂ Hydrogenation To Ethanol

Carbon dioxide is widely found in the atmosphere and water,which carbon content is more than 10 times that of traditional energy such as oil,natural gas and coal.It is about 10¹⁶ tons in nature.Excessive CO₂ content will cause greenhouse effect,ocean acidification and other environmental problems,posing a serious threat to the human survival environment,and the conversion of carbon dioxide into methanol,ethanol,hydrocarbons and other outstanding fuels and chemicals by hydrogenation has become a universally recognized better method.Because of its high energy density,transportation safety and important chemical raw materials,ethanol has become the preferred target product.First,this dissertation describes the design and preparation of VO_x-Rh/MCM-41which is practical and effective catalytic performance improvement for CO₂hydrogenation.The results showed that the mesoporous molecular sieve MCM-41could effectively promote the dispersion of Rh particles,and the catalyst of Rh/MCM-41 under the modification of VO_x showed excellent conversion and ethanol selectivity.The strong interaction between VO_x and Rh was determined by means of transmission electron microscope（TEM）,Raman spectrum and XPS.In addition,the active site,reaction intermediate species and reaction path were investigated by the in situ diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）and density functional theory（DFT）.In situ infrared results show that CO₂ adsorbed on the surface of the catalyst to form carbonate,formate and various forms of CO.The tilted CO adsorbed at the VO_x/Rh interfacial sites can be easily dissociated and hydrogenated to form*CH₃ species,CO is inserted to*CH₃ to form CH₃CO,and then CH₃CO is further hydrogenated to form ethanol.In addition,the design and preparation of ordered mesoporous structure CoAlO_xcatalyst were studied.Compared with the catalysts prepared by co-precipitation and impregnation method,the catalytic performance of m-CoAlO_x catalyst was found to be better.The structure of the catalyst was characterized by TEM and XRD,and we found m-CoAlO_x had ordered mesoporous structure.The physical and chemical properties of the catalyst were characterized by H₂-TPR and CO₂-TPD,and the doping ofAlinhibited Co₃O₄ reduction and enhanced CO₂ adsorption.In addition,we used in situ DRIFTS to study the intermediate species and reaction path of CO₂ hydrogenation reaction on the surface of m-CoAlO_x catalyst.The in situ infrared results showed that CO₂ was adsorbed and activated on the catalyst surface to generate CO₃^2-species,HCO₃^-and HCOO^-in turn generated after hydrogenation,and then inserted with*CH₃to generate CH₃COO^-as the C₂ intermediate species,and further hydrogenated to ethanol.