Study On Ni-based Catalysts In Dry Reforming Of Methane

Dry reforming of methane is a reaction that converting methane and carbon dioxide into syngas.As the most potential catalyst for industrial application,Ni-based catalysts are limited in industrial applications due to easy carbon deposition,sintering and fast deactivation.Therefore,it is of great theoretical and practical significance to improve the catalytic performance and carbon deposition resistance of nickel-based catalysts.In this thesis,three kinds of new catalysts were synthesized for the improvement of the carbon deposition resistance of the catalyst.The effects of different factors on the activity and carbon deposition resistance of the catalyst in dry reforming of methane were studied in order to obtain the relationship of structure and catalytic properties.Through the screening and optimization of supports and preparation methods,NiMgAl-LDH catalyst prepared by co-precipitation method was selected as the basic catalyst for further study,and the Ni loading amount and the preparation conditions of the catalyst were optimized.Ni_0.27Mg_2.73Al-LDH prepared by calcination at 550 ? in atmosphere has good catalytic performance after reduction by hydrogen at 850 ? for 1 h.By discussing the process conditions,it is concluded that the appropriate amount of inert filler can increase the effective utilization of the catalyst.When the amount of the catalyst is 0.15g,the amount of inert filler is 2g.The reaction performance was evaluated as the catalyst under the reaction conditions of a reaction temperature of 750?,a total feed gas flow rate of 220 mL/min,and the ratio of CO₂:CH₄:N₂ is 5:5:1.La-promoted NiMgAl mixed-oxide catalysts derived from hydrotalcite were synthesized by co-precipitation method for the carbon dioxide reforming of methane.The introduction of lanthanum into NiMgAl mixed-oxide catalysts reduced the reduction temperature of the catalysts.Lanthanum evidently improved the resistance of carbon deposition by increasing the basicity of the catalyst,forming the La₂O₂CO₃ phase and improving nickel metal dispersion.When the lanthanum content was 1.0wt%,the catalytic activity achieved the optimal value.Therefore,compared with NiMgAl catalyst,La-NiMgAl maintained higher reaction activity after 100 h reaction.Based on Ni_0.27Mg_2.73Al-LDH and 10wt%Ni/MgAl₂O₄ catalysts,SiO₂-coated of Ni-based catalysts were prepared.After analyze the experiment results it can conclude that the presence of coating layer of SiO₂ increased the interaction between the Ni metal particles and the supports,which inhibits agglomeration of the Ni particles on the surface of the catalyst,and the sintering growth of the Ni particles,thereby improving the stability of the catalyst and the carbon deposition resistance.Ni_0.27Mg_2.73Al-LDH@SiO₂ was partially coated catalyst,and 10wt%Ni/MgAl₂O₄@SiO₂ was completely coated catalyst.The Ni_0.27Mg_2.73Al-LDH@SiO₂ catalyst with hydrotalcite structure has not showed dual confinement.