The Modification Of Ordered Mesoporous Nickel-based Catalyst And Its Catalytic Performance In Methane Autothermal Reforming Reaction

Methane reforming is an attractive option that converts two harmful greenhouse gases(methane and carbon dioxide)into syngas(a mixture of H2 and CO),which is an important feedstock for the production of high value-added chemical products,such as methanol and liquid fuels.This dissertation focused on the modification of nickel-based catalyst.Three kinds of nickel-based catalysts modified with Neodymium(Nd),Zirconium(Zr)and Samarium(Sm)were synthesized and investigated in the methane reforming reaction.The textural of the promoted catalysts were characteried by using XRD,N2 adsorption-desorption isotherms,H2-TPR,CO2-TPD,TEM,XPS,TG analysis methods.The prominent role of the modification in changing the structure as well as in improving the catalytic performance were systematically illuminated.The main conclusions drawn from this research work are of practical significance in designing efficient ordered mesoporous nickel catalysts suitable for the reforming process.Firstly,Neodymium-promoted mesoporous silca NdMS were prepared through a sol-gel strategy.Nickel-based catalysts with high dispersion by using NdMS as supports were investigated for methane reforming with carbon dioxide and/or oxygen to produce syngas.NdMS supports and nickel catalysts were examined by combining textural,structural,local and surface information.The characterization results showed that Nd was successfully incorporated into the mesoporous framework of MS and Nd was beneficial to improve the metal dispersion.All Nd-promoted Ni/MS catalysts were effective for the methane reforming reaction.Ni/0.04 NdMS catalyst exhibited the highest initial catalytic activity during 12 h time on stream,which was attributed to its high metal dispersion,more basic sites and the strengthened nickel-support interaction.The readily deactivation and poorest catalytic activity of Ni/MS catalyst were due to the serious oxidation of metallic nickel under reaction medium.Secondly,the catalytic performance of zirconium doped catalysts NiZr/SBA-15 were prepared by co-impregnation method and investigated over methane reforming reaction.The addition of ZrO2 significantly improved the catalytic activity and stability of catalyst,and the optimum promoter loading was molar ratio of Zr/Si=0.02.The characterization results revealed that the Ni/SBA-15 doped with Zr had smaller metallic Ni size than undoped one,and the dispersion of NiO was improved.Moreover,the appropriate doping of zirconium played an important role in maintaining the hexagonal mesoporous structure during the reaction.Finally,nickel-based catalyst with samarium-modified SBA-15 mesoporous material were synthesized by one-pot methodand studied in the methane reforming reaction.The positive effect of samarium on the physical properties of mesoporous materials was analyzed in detail.It was found that the Sm-SBA-15 mesoporous material had excellent mesoporous properties and was a good carrier material for the catalytical application.The doping of Sm could decrease the particle size of Ni particles by 50% compared with undoped one.Besides,the Sm-containing catalysts exhibited higher metal dispersion and the specific surface area.The appropriate addition of Sm was a desicive factor in maintaining the higher metal dispersion and the regular hexagonal mesoporous structure.Based on these unique structural properties,the catalytic activity over Ni/Sm-SBA-15 catalysts was obviously improved.When the molar ratio of Sm/Si = 0.02,the maximum catalytic activity was achieved.