Preparation Of Modified Ni-based Catalysts And Their Catalytic Performance In Carbon Dioxide Reforming Of Methane

The catalytic reforming of CH₄ with CO₂ is industrially attractive not only because it yields syngas with H₂/CO ratio suitable for F-T synthesis, but also it can be used in some plant favorable circumstances to transform effluent containing CO₂ into valuable feedstock.In this thesis a series of nickel-based catalysts loaded on different substrates were prepared, and their catalytic reactivity in the reforming of methane with carbon dioxide were systematically investigated. In the first part, the reactivity and stability of the Ni/BaTiO₃ catalysts were studied with diffferent CH₄/CO₂ ratios. It is found that the stability of the Ni/BaTiO₃ decreases considerably when the CH₄/CO₂ ratio was 1.1 : 1. Moreover, the amount of carbon deposited on the catalyst reaches 60% after 1 hour reaction. This Ni/BaTiO₃ was further modified by using different precursors during the synthesis, and characterized with XRD, TPR and etc. The Ni/BaTiO₃ catalyst prepared with citrate precursor has a higher initial reactivity in the reaction. However, no improvement in catalyst stability is observed, because of the aggregation of the nano particles that leads to a poor dispersion of the reactive species.In the second part, composite support BaTiO₃/γ-Al₂O₃ was adopted for the nickel catalysts via sol-deposition method. The bulk structures and surface features of such catalysts were systematically characterized by XRD,FT-IR,BET and etc. Reforming of methane with carbon dioxide was used as a probe reaction to test the reactivity and resistance towards carbon deposition. We found that BaTiO₃ phase could be observed only when the loading is higher than 16.9wt%. XRD results demonstrate that BaTiO₃ can effectively prevent its aggregation when it is loaded on theγ-Al₂O₃ substrate. The reactivity of the catalyst does not change obviously with the amount of BaTiO₃ in the composite support. Nevertheless, the stability of the catalyst could be improved by increasing the annealing time and temperature (e.g., the obtained catalyst is still active after 20 hours' reaction and has only 20% carbon deposition). TPR results show that NiO has a strong interaction with the composite support, which leads to a smaller Ni species and higher resistance to aggregation.