Studies On The NiO-based Catalysts For Decomposition Of Methane

Methane contains the highest hydrogen content in hydrocarbons, so it is one of the most efficient raw materials to produce hydrogen. However, extremely high energy is needed to break the C-H bond because of its high band energy. Therefore, methane decomposition involved with catalyst is attracting more and more attention due to its low reaction temperature.To study the methane decomposition of NiO-based catalyst, the following aspects were focused on. Firstly, NiO-based catalysts supported on γ-Al₂O₃ and MgAl₂O₄ were prepared by impregnation, respectively. Then, the physicochemical properties of these catalysts were characterized by XRD, N2 absorption-desorption, TG-DTG, etc. Finally, the activity source of NiO-based catalyst, the catalytic mechanism and the influencing factors of catalytic performance were discussed by analyzing characterization and experiment results of reactions in a micro-fixed bed reactor.The study results showed that NiO which had little interaction with support reacted with CH4 firstly. During the process, H₂ O, CO, CO2 and metal Ni were generated. Meanwhile, Ni aggregated as the reaction progress. When metal Ni aggregated to a certain degree, it further catalyzed CH4 decomposition to produce H₂. Besides, both the CH4 initial conversion and the oxide products were influenced by the concentration of NiO which had little interaction with support. The higher concentration of this kind of NiO was, the more CH4 would be converted initially. And the order of the easness to form oxide products was H₂O<CO<CO2. Among these oxide products, CO2 was produced by the secondary oxidation of CO, and it would be produced only when the NiO mentioned above was enough.The research also revealed that the catalytic performance of NiO/MgAl₂O₄ was better. The appropriate interaction between NiO and MgAl₂O₄ made it more initially active. And the larger specific surface of MgAl₂O₄ contributed to better dispersion of the reduced Ni and improved H₂ selectivity. In addition, both the catalyst preparation conditions and the operation conditions affected the catalytic performance of NiO/MgAl₂O₄. The results were discussed as follows. Firstly, increasing the calcination temperature appropriately intensified the interaction between NiO and MgAl₂O₄, enhanced the dispersion and stability of NiO, and then improved H₂ selectivity. Secondly, extending H₂ pre-reduction time decreased the concentration of the lattice oxygen, so CH4 initial conversion was reduced but H₂ selectivity was improved. Thirdly, high reaction temperature was helpful to enhance the activity of the lattice oxygen and the metal Ni, it thus improved the catalyst activity and selectivity. At last, smaller space velocity improved the initial CH4 conversion but had little influence on H₂ selectivity.