Confined Ni-Based Catalyst:Preparation And Application In Methane Dry Reforming

With the increase in global greenhouse gas emissions（mainly methane and carbon dioxide）,the trend of global warming is gradually increasing.In order to solve this environmental problem,people will focus on the development of green and sustainable energy sources,such as hydrogen and biomass.Dry reforming of methane（DRM）can effectively convert methane and carbon dioxide,two resource-rich and inexpensive greenhouse gases,into more valuable compounds.Ni-based catalysts are widely used because of their low cost,high initial activity,and abundant raw materials.However,Ni-based catalysts used in DRM reactions are prone to sintering and carbon deposition during the reaction,resulting in rapid catalyst deactivation.Therefore,for practical applications,it is necessary to develop an efficient catalyst that can withstand high temperatures and resist deactivation due to carbon deposition and sintering problems.In this study,we designed and synthesized two kinds of La₂O₃-Ni@MgAl₂O₄ and Ni-Ce O₂@SiO₂ catalysts with high efficiency on the basis of a thorough understanding of DRM reaction mechanism,as well as catalyst structures and surface properties.These two catalysts were applied to the DRM reaction,and a series of characterization methods were used to explore the relationship between the physical and chemical properties of the catalyst and its reaction performance.Part 1:Ni@MgAl₂O₄,La₂O₃-Ni@MgAl₂O₄ and La₂O₃-Ni/MgAl₂O₄ catalysts were prepared by one-pot method and equal volume impregnation method.In the dry gas reforming of methane（DRM）reaction,the catalytic activity of the La₂O₃-Ni/MgAl₂O₄ catalyst remains stable regardless of whether it is reacted at 800^oC or at 700 ^oC.The catalyst was characterized by XRD,TEM,N₂-adsorption desorption,H₂-TPR,Raman and in-situ infrared.The results show that La₂O₃-Ni@MgAl₂O₄ catalyst has good metal dispersion,the most excellent pore structure,superior redox performance and carbon deposition resistance.In addition,the La₂O₂CO₃ formed by the auxiliary agent La₂O₃ adsorbing and activating CO₂ can inhibit the formation of coke deposits,thereby improving the anti-coking performance of the catalyst.Part 2:Ni-Ce O₂@SiO₂ catalyst and two supported（Ni-Ce O₂/SiO₂,Ni/SiO₂）catalysts were prepared by reverse microemulsion method and equal volume impregnation method,respectively.The Ni-Ce O₂@SiO₂ catalyst has the most excellent catalytic activity at different reaction temperatures,and shows good stability at 800 ^oC for 100 hours or 600 ^oC for 20 hours.XRD,N₂-adsorption and desorption,H₂-TPR,O₂-TPD,H₂-TPD and thermogravimetric characterization were used to analyze the structure,surface species and redox properties of the catalyst.Studies have shown that the core-shell structure of Ni-Ce O₂@SiO₂ catalyst and Ce O₂ increase the number of active oxygen species,improve the dispersion of Ni and the interaction between the support,and make it exhibit excellent anti-carbon deposition and anti-sintering properties.In addition,the in-situ infrared results show that the DRM reaction follows the L-H mechanism on the catalyst,and the oxygen species provided by Ce O₂ can react with the carbon to form CO,thereby inhibiting the formation of carbon deposits,thereby improving the anti-coking performance of the catalyst.