Superior catalytic behavior of trace Pt-doped Ni/Mg(Al)O in methane reforming under daily start-up and shut-down operation

Doping effects of Pt and Ru on Ni/Mg(Al)O catalysts were compared in daily start-up and shut-down operations of steam reforming of CH₄. Trace Pt-doped catalyst showed better behavior than trace Ru-doped catalyst; the former was self-activated but the latter was not, although both exhibited self-regenerative activity. Moreover, the former exhibited sustainable activity, although the latter was quickly passivated, in the autothermal reforming of CH₄. Formation of Pt-Ni alloy on the surface of fine Ni metal particles on the catalysts was suggested by EXAFS analyses. CH₄ was dissociatively activated to form hydrogen on Pt, assisted by adsorbed O or OH species, leading to the self-activation via Ni reduction by hydrogen spillover from Pt. The self-regeneration of the Pt-Ni/Mg(Al)O catalysts can be achieved by the continuous rebirth of active Ni metal species via reversible reduction-oxidation between Ni⁰ and Ni²⁺ in/on Mg(Ni,Al)O periclase assisted by the hydrogen spillover.