The origin of the exceptional properties of a Ni10Ce90 mixed oxide relative to a Ni/Al2O3 catalyst (i.e., immediate activity without catalyst prereduction, high resistance toward coking, high catalytic activity) and its catalytic deactivation for the CO2 reforming of methane was investigated by XRD, XPS, pulse experimentation, and regeneration tests. Based on those results, a reaction mechanism is proposed. First, the catalytic property with no prereduction step relies on the reactivity of oxygen contained in the Ni phase. The rapid activation of Ni10Ce90 is based on the active interfacial oxygen in the Ni-Ce boundary, which leads to the complete oxidation of methane and the creation of active sites for the subsequent reforming reaction, whereas a slow decomposition of NiAl2O4 spine] results in a long induction period of the Ni/Al2O3 catalyst. Second, the coking resistance as well as the catalytic activity rely on the reactivity of lattice oxygen in the ceria. The ceria lattice oxygen participates in the reforming reaction through migration, which leads to the formation of oxygen vacancies. Subsequently, the vacancies are completely supplemented by oxygen arising from the dissociative adsorption Of CO2. Finally, the stability of Ni10Ce90 relies on the balance between the rate of generation and supplement of oxygen vacancies. Unbalanced rates of these processes result in deactivation. (c) 2007 Elsevier Inc. All rights reserved.