Study On Composite Oxide Catalysts For Catalytic Upgrading Of Ethanol To 1,3-Butadiene

The use of biomass ethanol as a raw material to produce 1,3-butadiene?hereinafter referred to as butadiene?can overcome the problem of using non-renewable raw materials in the current production process,therefore it has a good development prospects and has received researchers'attention.The production of butadiene from ethanol consists of five consecutive steps:ethanol dehydrogenation to acetaldehyde,aldol condensation of acetaldehyde to 3-hydroxybutyraldehyde,3-hydroxybutyraldehyde dehydration to crotonaldehyde,selective hydrogenation of crotonaldehyde to crotyl alcohol,and crotyl alcohol dehydration to butadiene.Due to the complexity of the reaction system that requires the cooperation of multiple active sites,the design of catalysts with multiple active sites is demanded for good catalytic results.In recent years,the research on catalysts has made great progress,from mixed metal oxides to Si O₂supported multi-component metal oxides,and to current zeolite catalysts.Although through different experimental methods,researchers have a deeper understanding of the reaction,but it is still insufficient in terms of industrial application.It is necessary to ensure the stability of the catalyst while improving the reaction activity.Herein,the relationship between the acidity and basicity of catalysts with the activity of key reaction steps,the butadiene selectivity and yield in the process of ethanol to butadiene was explored.Zn-M?M=Cu,Mg,Ce,La,Ga?/SBA-15 was synthesized as catalysts.Through the evaluation of catalyst activity,the calculation of key step activities,and the measurement of acidity and basicity of catalysts,relationships between the strength and quantity of acid and basic sites of catalysts with the activity of ethanol dehydrogenation,that of acetaldehyde condensation,that of MPVO reaction,butadiene selectivity,and butadiene yield were obtained.We found that weak acid and moderate basic sites are benefical for the ethanol dehydrogenation,while moderate acid sites cause the ethanol dehydration.Moreover,the selectivity and yield of butadiene are related to acetaldehyde condensation and MPVO activities.Secondly,we used SBA-15 as support and adopted a wetness impregnation method to prepare a series of catalysts.After screening evaluation of catalyst activity,including the composition and content of metal oxides,5Zn-3Zr/SBA-15 catalyst showed good catalyst activity.Subsequently,a series of characterization techniques was applied to analyze the physical structure and chemical properties of catalysts.Coupling with experimental data,we found that SBA-15 can provide a large specific surface area,which is conducive to the dispersion of metal oxides on the support.Zn O mainly plays the role of catalyzing the dehydrogenation of ethanol,while Zr O₂ mainly catalyzes acetaldehyde condensation and the selective hydrogenation of crotonaldehyde.When Zn O and Zr O₂ are co-loaded on SBA-15,the ethanol dehydration activity of Zr O₂ is greatly reduced.It was found by XPS that the state of metal oxides is changed compared with the single component of Zn O and Zr O₂supported on SBA-15.Finally,we used different catalyst preparation methods to synthesize5Zn-3Zr/SBA-15 catalysts,and found that the catalysts prepared by the wet-kneading,co-precipitation in the channel and the two-step impregnation method were not as active as the one prepared by the wetness impregnation method.We then used an additives in catalyst preparation and removed them during the catalyst calcination process,and found that the use of polyethylene glycol can further increase the yield of butadiene.