Preparation And Performance Of SiO₂ Supported Ni-based Catalysts For Carbon Dioxide Reforming Of Methane Reaction

In recent decades,with the spur of human social and global economic,the level of environmental damage to the natural was continuously increasing and the energy sources depletion was threatening the world.Human confront with the double test of energy and environment.As one of the high-temperature heterogeneous catalytic reactions,carbon dioxide reforming of methane reaction that converts methane?CH₄?and carbon dioxide?CO₂?into syngas is conducive to the mitigation of greenhouse effect and the efficient utilization of methane resources.At the same time,carbon dioxide can be converted into useful chemicals or liquid fuels,carbon resources can be recycled.Therefore,carbon dioxide reforming of methane reaction is an green and high-efficiency reforming technology with the industrial feasibility,which has produced a new wave of research upsurge.There are two problems in the study of catalysts for carbon dioxide reforming of methane reaction.Firstly,due to the limitation of thermodynamics,the reaction can only achieve high conversion rate at high temperature,whereas the catalytic performances of most catalysts at low temperature are not ideal.However,the active component of catalysts is prone to sintering at high temperature,resulting in poor catalytic stability.Secondly,the precursor of carbon in the intermediate products will form carbon deposition,because it is unable to rapidly gasify during the process of reaction,resulting in lower yield and shorter catalyst life.In the research of Ni catalysts,the size effect of catalyst Ni particles and the interaction between the mental and support are considered as significant factors affecting the catalytic performance,which can effectively inhibit the sintering and carbon deposition of Ni particles and improve the performance of catalysts.According to the above two factors,Ni catalysts with super small size and sintering resistance were designed and applied to carbon dioxide reforming of methane reaction.The main results presented in the dissertation have be summarized as followings:?1?The supported Ni/SiO₂-E catalyst was successfully synthesized by strong electrostatic adsorption.Compared with the Ni/SiO₂-I catalyst prepared by traditional impregnation method,the nickel nanoparticles were smaller in size and its interactions between metal carriers were stronger.The smaller Ni size,the less deep cleavage of the CHx intermediate,and the lower the carbon deposition.The strong interaction limits the migration and aggregation of Ni,and improves the activity and stability of carbon dioxide reforming of methane reaction over Ni/SiO₂ catalysts.?2?Core-shell catalyst Ni@SiO₂ containing ultrafine nanoparticles prepared by microemulsion method was calcined at 500?-700?.The effects of calcination temperature on size Ni particles,metal-support interaction and catalytic performance of on Ni@SiO₂ catalyst were studied.The results showed that the higher calcination temperature is,the larger the Ni particles and the stronger the interaction between Ni and SiO₂ will be.The tests revealed that the activity and stability of Ni@SiO₂ catalyst were determined by the combined effects of Ni particle size and metal-support interaction.When the calcination temperature was 600?,the two factors reached the best match and the catalytic performance of the catalyst was the most excellent.?3?Ni@SiO₂ catalyst was modified by CeO₂,and core-shell structure?Ni/CeO₂?@SiO₂catalyst containing Ni and CeO₂ nanoparticles was designed and prepared.Compared with the Ni@SiO₂ catalyst,the size of Ni particles of?Ni/CeO₂?@SiO₂ catalyst is smaller,the metal-support interaction was stronger,the sintering degree of Ni particles was limited,and the carbon deposition was decreased.Therefore,the catalytic activity and stability of carbon dioxide reforming of methane over catalyst?Ni/CeO₂?@SiO₂ were significantly improved and the catalytic performance of core-shell Ni catalyst were optimized.