Study On Perovskite-oxide Catalysts For Ethanol Steam Reforming Reaction To Produce Hydrogen

In the chemical industry,the synthesis gas(H2 + CO)is used as the intermediate product,which can produce many chemicals and fuels with high added value.Currently,ethanol steam reforming(ESR)is one of the most environmentally friendly and economical ways to prepare H2 + CO.However,the high steam partial pressure and high temperature in the ESR process are a major challenge for the design of stable and efficient catalysts.In recent years,the research foucs of ESR reaction is how to improve the stability of the catalyst.This paper focuses on improving the performance of resistance of carbon deposition and sintering.Based on these two points,the first two parts of this paper,we choose the metal Ni as the active component of the catalysts,and the low cost and high activity are the natural advantages of Ni based catalysts.According to the disadvantages of Ni based catalysts which are easy to sintering and carbon deposition,we propose the following design ideas: Firstly,add a second component into the perovskite sample to form an alloy catalyst;Secondly,modify the perovskite structure to prepare a three-dimensionally ordered pore structure perovskite sample with high specific surface area.In the last part,we discuss the feasibility of perovskite oxide as the catalyst directly using in ESR reaction.Firstly,Zn substituted LaNiO3 perovskite oxide with a general formulae LaNi1-xZnxO3-δ(x = 0,0.05,0.10,0.15,0.20)are synthesized with a one-step citrate method and evaluated as the catalyst precursor in ESR reaction.The Zn doped catalysts present good catalytic performance and stability in the ESR reaction,especially the LaNi0.85Zn0.15O3-δ catalyst.Zn substituted samples are more difficult to reduce.This is due to the strong bond of La-O-Zn which favors the formation of small Ni particles,meanwhile,the stronger band of Zn-O-La than that of Ni-O-La suppresses the sintering of Ni(or Ni-Zn alloy)particles.Besides,the doping of Zn effectively improves the resistance to coking.The electron donation effect of Zn to the surface nickel and the mobile oxygen spilled over from ZnO contribute to the carbon resistance.The spillover oxygen from ZnO facilitates the redox cycle of active metal and effectively inhibits sintering of metal particles.Secondly,high surface area of three-dimensionally ordered macroporous/mesoporous(3DOM/m)La1-xCexNiO3-δ(x=0,0.1,0.2,0.3)catalysts are successfully synthesized and are first used in ESR reaction.The experimental results show that the catalyst of La0.7Ce0.3NiO3-δ with 3-DOM/m structure exhibits the best catalytic activity and stability in the ESR reaction.The 3-DOM/m structure provides a large specific surface area,which is beneficial to mass transfer,improves the utilization of the active component Ni,and finally improves the catalytic performance of the catalyst.Next,the 3-DOM/m structure is conducive to the formation of small particles of metal Ni,and effectively prevent the agglomeration of Ni particles,inhibit the sintering of active components,thereby improve the stability of the catalyst.In addition,3-DOM/m structure can effectively inhibit ethylene,thereby inhibiting coking production.Eventually,a series of La0.75Sr0.25CrxMn1-xO3-δ(X=0.1,0.3,0.5)perovskite oxide are synthesized with a one-step citrate method and directly used as the catalyst precursor in ESR reaction.The results show that the La0.75Sr0.25Cr0.5Mn0.5O3-δ has the best catalytic activity for the ESR reaction.Although the yield of H2 is low,the Scanning Electron Microscope(SEM)and Raman results indicat that no carbon species are formed on the catalyst surface after 10 h reaction.This provides a new way for ESR reaction to inhibit carbon deposition and improve the stability of the catalyst.