Study On The Ni Active Species For Carbon Dioxide Catalytic Reforming Of Methane

Recently,considerable attention has been paid to the carbon dioxide reforming of methane?CRM?due to environmental protection as well as potential industrial application aspects.This reaction consumes two greenhouse gases simultaneously to produce valuable synthesis gas,which is the basic reactant for many valuable chemicals.Various catalysts have been employed and Ni catalysts show a great potential with regard to economic and availability aspects.A major obstacle for the catalyst application in this reforming process is deactivation mainly due to coke accumulation and sintering of both support and metal particles.It is important to prepare efficient and stable catalysts for the CRM.In the research,three catalysts of Ni-Mg/?-Al₂O₃,Ni/MgAl₂O₄ and Ni_0.5Mg_0.5Al₂O₄ with the same compositions are prepared by incipient wetness impregnation,sol-gel method,and were tested in CRM reaction.The structure and surface properties of catalysts are characterized by XRD,H₂-TPR,H₂-TPD,BET and TEM etc.The results indicate that catalysts of Ni-Mg/?-Al₂O₃ and Ni/MgAl₂O₄ show low metal dispersion and poor sintering resistance ability,and sizes of nickel particles increase obviously and carbon deposits during the reaction.While the Ni_0.5Mg_0.5Al₂O₄ catalyst exhibits high activity and stable catalytic performance,Ni²⁺ cations in Ni_0.5Mg_0.5Al₂O₄ are incorporated into the spinel lattice,which endow this catalyst with a high metal dispersion.Ni_0.5Mg_0.5Al₂O₄ catalyst is significantly coking-resistant owing to dispersion of nickel nanoparticles.The composition effect of Mg_1-xNi_xAl₂O₄?x=0.2,0.3,0.5,0.7?is investigated on the structure and properties of catalysts.The results show that catalytic performance exhibits a maximum at x=0.5,methane conversion is up to 87%,and good stability of the catalysts.H₂-TPD results show that nickel is highly dispersed on the catalysts with lower content of nickel,the dispersion is ca 20%.Nickel content increased?x = 0.7?,nickel dispersion is declined obviously,its value is only 12.4%.TG analyses indicate that catalysts with x?0.5 exhibit smaller amounts of carbon deposition than the Mg_0.3Ni_0.7Al₂O₄,and thus superior tolerance to deactivation.