Ni/Nlg(Al)O catalysts doped with trace Ru showed self-regenerative activity during a daily start-up and shut-down (DSS) operation of steam reforming of methane. Formation of Ru-Ni alloy on the surface of fine Ni metal particles on the catalysts was strongly suggested by EXAFS and TPR measurements. The Ni/Mg(Al)O catalyst was passivated by the oxidative incorporation of Ni-0 to Ni2+ in Mg(Ni,Al)O periclase, and trace Ru assisted the regeneration of Ni metal from the Ni2+ by hydrogen spillover. Even notably sintered Ni metal particles on the Ni/Mg(Al)O catalyst by steaming were rapidly redispersed, resulting in the revelation of the high and stable activity during the DSS operation. The self-regeneration of the Ru-Ni/TMg(Al)O catalysts can be achieved by the continuous rebirth of active Ni metal species assisted cooperatively by both Ni2+ -> Ni-0 reduction by hydrogen-spillover via trace Ru metal or Ru-Ni alloy and reversible reduction-oxidation between Ni-0 and Ni2+ in Mg(Ni,AI)O periclase. (c) 2007 Elsevier Inc. All rights reserved.