Studies Of Carbon Dioxide Reforming Of Methane Catalyzed By Nickel Based Catalysts Supported On CeO₂

With the continuous growth of the global economy,energy and environment have become two important factors affecting human development.The current world energy system is more focused on finding more energy and lower carbon emissions.If the carbon dioxide produced by human life could be effectively converted,it would be a major step forward in human development.According to the annual report on China’s CO₂ utilization technology and project,carbon dioxide can be made high value chemicals,including dry reforming of methane reaction（DRM）,namely,carbon dioxide reforming of methane reaction（CRM）,can make full use of methane and carbon dioxide,and then into the important industrial raw material ratio of 1:1 syngas（CO+H₂）,further into highly effective clean fuel and other high value-added chemicals.This reaction is of strategic importance in the field of energy and the environment,and the preparation of a catalyst to enable the industrialization of this reaction is a top priority.After years of research,scientists have found that low-cost Ni-based catalysts have high catalytic activity for methane carbon dioxide reforming reaction.It is a pity that Ni-based catalysts have not been used in industrial applications because of their easy deactivation under high temperature reaction conditions.In the dry reforming of methane,the overall structure of the support,active metal,auxiliary agent and catalyst affects the catalytic reaction together,so the selection and control of the structure of each component in the catalyst is the key to solve the problem.The theme of this thesis is to develop catalysts with low energy consumption,high activity and good stability.Based on this theme,the structure of Ni based catalyst was designed and modified accordingly.In the first part of this paper,the light yellow granular CeO₂ carrier was obtained by direct calcination of cerium nitrate with air at 350℃,and then the CeO₂ carrier was calcined under different atmospheres（Air、NH₃、N₂ and H₂）,and the carriers were recorded as CeO₂-Air、CeO₂-NH₃,CeO₂-N₂ and CeO₂-H₂,respectively.Finally,Ni/CeO₂ series catalysts were prepared by impregnation method,and the phase structure of the support and catalyst was characterized.The catalytic performance of DRM reaction was tested.Comparing the catalytic performance of the catalysts,it can be seen that doping basic n promoter into CeO₂ support after high temperature nitriding treatment can increase the initial activity of the catalysts at 450℃,i.e.0.8%→8.1%（based on CH₄ conversion）.The results show that CeO₂ support doped with basic N is of great significance to improve the catalytic performance of the catalyst and save energy.In the second part,the rod-like CeO₂ support（CeO₂-R）synthesized by hydrothermal method was nitrided by high temperature NH₃,and some oxygen atoms in the rod-like CeO₂ carrier were replaced by nitrogen atoms to obtain the nitrided rod-like CeO₂ support（N-CeO₂-R）.At the same time,ordinary granular CeO₂（CeO₂-P）、nitrided granular CeO₂ support（N-CeO₂-P）、Cubic CeO₂ support（CeO₂-C）and Nitride Cubic CeO₂ support（N-CeO₂-C）were synthesized as comparison,and Ni/CeO₂ series catalysts were prepared by impregnation method,and the phase structure of the support and catalyst was characterized.The catalytic performance of DRM reaction was tested.The 6%Ni/N-CeO₂-R catalyst with high temperature NH₃ nitriding treatment has the highest catalytic activity and relatively stable stability.6%Ni/N-CeO₂-R catalyst has more exposed surface,smaller Ni particles with higher dispersion,stronger metal support interaction,higher Ni^δ+and O_II content on the surface,more CO₂ molecules can be adsorbed and the carbon deposition on the surface of the catalyst can be effectively converted,thus improving the catalytic activity,stability and anti carbon deposition performance.Finally,in the third part,The Ni/CeO₂ catalysts with different morphologies synthesized in the second part were used as supports sources to prepare Ni/CeO₂catalysts.The preparation method was precipitation deposition method,and then calcined in NH₃ atmosphere at 700 ^oC for 4h to obtain the nitrided Ni/CeO₂ catalyst.At the same time,the prepared catalyst was characterized and its catalytic performance was tested.There are more oxygen vacancies and defective CeO_1.66 in the 6%Ni/CeO₂-R catalyst.The metal support interaction is strong.The basic N promoter can promote the adsorption and dissociation of CO₂ and effectively eliminate the carbon on the surface of the catalyst.The catalytic performance and anti carbon deposition performance of the catalyst are improved significantly.