"Green" preparation of "intelligent" Pt-doped Ni/Mg(Al)O catalysts for daily start-up and shut-down CH₄ steam reforming

"Green" preparation of "intelligent" catalysts for daily start-up and shut-down steam reforming of CH₄ for the reformer of the PEFCs has been investigated; trace Pt-doped Ni/[Mg_xAl]O (x = 0.5, 1.3 and 3.5) catalysts were prepared starting from commercial Mg_x-Al hydrotalcites (HTs) by adopting a "memory effect" of HT. The Mg_x-Al HTs were calcined to the mixed oxides, i.e., [Mg_xAl]O, and were sequentially impregnated with aqueous solutions of Ni(II) nitrates and Pt(IV) nitrates. When [Mg_3.5Al] HT was calcined to [Mg_3.5Al]O at 850 °C, well grown Mg(Al)O periclase structure was formed. After impregnating [Mg_3.5Al]O powders in Ni(II) nitrate solution at 80 °C for 2 h, 10 wt% Ni was completely incorporated by reconstituting Mg(Ni)-Al HT due to the "memory effect", resulting in a high and sustainable activity due to the formation of self-regenerative Ni(-Pt) particles after 0.05 wt% Pt doping. The catalyst exhibited "intelligent" properties, i.e., self-activation and self-regenerative activity; the finely dispersed Ni(-Pt) particles were effectively self-regenerated via a reversible reduction-oxidation between Ni⁰ and Ni²⁺ on/in Mg(Ni,Al)O periclase. An increased Ni loading to 16 wt% on [Mg_3.5Al]O produced Ni(OH)₂ separately from the Mg(Ni,Al)O lattice, leading to the formation of non self-regenerative Ni(-Pt) particles even after 0.1 wt% Pt doping. We conclude that the well grown Mg(Ni,Al)O periclase structure acts as an effective Ni reservoir, through which Ni(-Pt) particles were self-redispersed via oxidative Ni incorporation and reductive Ni release assisted by steam and hydrogen spillover, respectively.