Modified Ni-based Core-Shell Catalysts:Preparation And Application For Dry Reforming Of Methane

Nowadays,the phenomenon of Greenhouse Effect is becoming more and more serious because of the excessive emission of greenhouse gases?such as CH₄ and CO₂?.The development and utilization of the clean and pollution-free energy is urgent,which is one of the tense strategies to solve the energy problem in our country.Hydrogen energy as clean fuel has potential application value.Methane dry reforming reaction is a effective way to reduce greenhouse gas emissions?CH₄ and CO₂?and synthesize recyclable and zero pollution syngas?H₂ and CO?.Ni based catalyst is considered to be the most likely high efficient catalyst for dry reforming of methane in industrial production due to its high activity and low cost.However,Ni based catalysts used to deactivate during the reaction due to the sintering or carbon deposition of Ni active components.In this work,two kinds of catalysts,ZrO₂-Ni@SiO₂ and In_xNi@SiO₂,were synthesized by doping metal oxide ZrO₂ and metal In modified Ni@SiO₂ catalysts for dry reforming of methane respectively.?1?Preparation of polycore core-shell ZrO₂-Ni@SiO₂ catalyst and its application in methane dry gas reforming.ZrO₂-Ni@SiO₂ and Ni@SiO₂ catalysts with multicore core-shell structure were synthesized by inverse microemulsion method.ZrO₂-Ni/SiO₂ supported catalysts were prepared by equal volume impregnation method and used in methane dry gas reforming.The results showed that ZrO₂-Ni@SiO₂ catalyst showed the best catalytic performance in this reaction.The conversion of CH₄ and CO₂ remained high during 240 h continuous reaction and there was no sign of deactivation,but the activity of the two kinds of catalysts decreased rapidly.Then the ZrO₂-Ni@SiO₂ catalyst was characterized by various characterization methods.TEM result shows that the catalyst still maintained a good core-shell structure before and after the reaction,with the polynuclear Ni or Ni-ZrO₂active components was coated by the SiO₂.The Ni particles with a size of 3.4 nm display insignificant change after 240 hours of catalyst reaction.XPS testified that most of the active components of Ni or Ni-ZrO₂ were distributed in the middle of SiO₂ core-shell.CO₂-TPD results show that the addition of ZrO₂ could provide more alkaline sites for the catalyst.The catalyst with the modification of ZrO₂ possess better Ni dispersion according to the H₂-TPD results.Besides,the catalyst modified by ZrO₂ can effectively improve the ability of anti-carbon deposition,which could be identified by the of TGA-DSC and Raman results.Thus,the activity and stability of modified catalyst have been improved.?2?Preparation of silica limited domain In-Ni alloy catalyst and its application in methane dry reforming.A series of In-Ni@SiO₂ catalysts with different in content were synthesized by inverse microemulsion method for methane dry reforming.The physicochemical properties of the catalysts were characterized by various characterization methods.TEM and XRD results table there is the formation of Ni₂In alloy in the catalyst.The results of XPS show that the doping of In increases the electron cloud density on Ni,and the side reaction of methane deep cracking can be controlled to varying degrees due to the increase of electron cloud density on active phase metal Ni,thus decrease the amount of carbon deposition in the reaction process.The results of activity test show that the doping of a small amount of In the catalyst has little effect on the activity of the catalyst,but it can effectively improve the anti-carbon deposition performance of the catalyst,which result in a good stability of catalyst.However,the excessive doping of In leads to the decrease of methane activation performance and the decrease of its reaction activity.The In_7.0Ni@SiO₂catalyst with the highest content of In has no activity.The In_0.5Ni@SiO₂ catalyst maintain a excellent reaction activity at 800^oC and the carbon deposition was only 4.3%even after 430h,which could be identified by the TGA-DSC and Raman resluts.