Preparation Of Highly Stable Ni/Al₂O₃ Catalyst And Study On Its Dry Reforming Performance Of Methane

The technology of“negative emission”of CO₂ is the key to achieve the carbon peak and neutrality targets.The development of carbon capture,storage and utilization technology is the core to realize the"negative emission"of carbon dioxide.CH₄ is the main component of natural gas,which is extremely abundant in the world.Meanwhile,shale gas and biological natural gas also provide a wider range of sources.The urgent treatment of CO₂ and the large amount of CH₄ resources provide the feasibility of reforming reaction in which methane and carbon dioxide as raw materials.Dry reforming of methane(DRM)is considered as an efficient way to convert both greenhouse gases,CO₂ and CH₄,into syngas(CO and H₂)and ultimately into other high-value chemicals.Ni-based catalysts are considered as the most promising catalysts for industrial application due to their low price and high catalytic activity.However,carbon deposition and sintering of active metal components at high temperatures can easily lead to deactivation of catalysts,which will result in the rapid activity decline of DRM.And this is the main obstacle for the application of DRM technology.Therefore,it is urgent to develop the high activity of Ni-based catalysts with high stability to inhibit the sintering and carbon deposition to meet the practical application requirements of DRM.A surface spatial confinement strategy provided by the dendritic layered structure is an efficient way to restrain the migration and sintering of metals or metal oxides.In this work,we intend to prepare highly stable Ni-based catalysts by rational design and regulation of the structure of Ni-based catalysts,so as to achieve long-term stable operation of DRM reaction.Firstly,Al₂O₃ with branch lamellar structure was prepared,and then Ni/HH-Al₂O₃catalyst was prepared by impregnation method.The lamellar structure of Ni/HH-Al₂O₃ can realize the separation of Ni particles,which increases the difficulty of Ni particle migration and weakens the sintering of Ni particles.In addition,the structure of the branch opening is conducive to the diffusion of reaction molecules,thus providing high reactivity.The stability test of DRM reaction at 700?for 100 h shows that the CH₄ and CO₂ conversion of10Ni/HH-Al₂O₃ remain 80%and 85%,respectively,indicating the long-term stability for DRM.After DRM reaction at 800?for 20 h,the conversion of CH₄ and CO₂ remain about93%and 97%,respectively,showing high temperature stability.The further experiments show that Ni/Al₂O₃ and Ni Al₂O₄ can achieve reversible transformation in the atmosphere of alternating oxidation-reduction to complete the regeneration of the catalyst.In next chapter,the surface spatial confinement strategy was extended to Ni/Al₂O₃catalysts with high Ni content by combining with the structural advantages of hydrotalcite.In the previous chapter,the surface spatial confinement effect of 10Ni/HH-Al₂O₃ is only effective when the Ni content is less than 15 wt%.We prepare Ni-Al hydrotalcite with branched structure to achieve the surface spatial confinement effect over Ni/Al₂O₃ catalyst with high Ni content.At the same time,this strategy has been extended to other hydrotalcite,such as Co-Al hydrotalcite and Cu-Al hydrotalcite.The performance test of DRM reaction at700?for 10 h shows that the CH₄ and CO₂ conversion of 80Ni/H-Al₂O₃ remain about 73%and 77%,respectively,and the H₂/CO ratio also remains about 0.83.Compared with80Ni/HH-Al₂O₃ and 80Ni/C-Al₂O₃ catalysts,80Ni/H-Al₂O₃ catalysts have higher stability.This work provides an effective method to prepare hollow layered catalysts with hydrotalcite structure as precursor,and the prepared catalysts have high stability in DRM reaction.