Methane reforming reactions over stable Ni/ θ -Al₂O₃ catalysts

NiO/θ-Al₂O₃ catalysts were prepared and investigated after reduction treatment in the methane conversion reactions, such as oxy-reforming, steam reforming and oxy-steam reforming. Among the catalysts with various Ni loading, 12% Ni loading exhibits not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between Ni and support results in forming stable NiO_x species. Reducibility of NiO and the population of NiO_x compared with NiO and/or NiAl₂O₄ play very important roles in the catalytic activity and stability of Ni/θ-Al₂O₃. Metallic Ni sites formed from the reduction of both NiO weakly interacting with the support and NiO_x strongly interacting with the support are active sites for methane reforming reactions. Even though free NiO sites are prerequisite for high activity, the increase of NiO population in high Ni loading favorably promotes Ni sintering resulting in undesirable catalytic properties.