Methane-reforming reactions over Ni/Ce-ZrO₂/θ-Al ₂O₃ catalysts

NiO/Ce-ZrO₂/θ-Al₂O₃ catalysts were prepared and investigated after the reduction treatment in methane-reforming reactions such as steam reforming and oxy-steam reforming. Among the catalysts with various Ni loading values, 12% Ni loading exhibited 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. It is speculated that the populations of NiO_x compared with NiO and/or NiAl₂O₄ play very important roles in the catalytic activity and stability. Metallic Ni sites reduced from NiO_x species strongly interacting with the support are active sites for methane-reforming reactions and have high coke resistance. The high activity and stability of Ni/Ce-ZrO₂/θ-Al ₂O₃ is due to a Ce-ZrO₂ layer precoated on θ-Al₂O₃, which plays a role in forming stable NiO_x species rather than free NiO or inactive NiAl₂O ₄ and in giving mobile oxygen species.