“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/[MgxAl]O (x = 0.5, 1.3 and 3.5) catalysts were prepared starting from commercial Mgx–Al hydrotalcites (HTs) by adopting a “memory effect” of HT. The Mgx–Al HTs were calcined to the mixed oxides, i.e., [MgxAl]O, and were sequentially impregnated with aqueous solutions of Ni(II) nitrates and Pt(IV) nitrates. When [Mg3.5Al] HT was calcined to [Mg3.5Al]O at 850 °C, well grown Mg(Al)O periclase structure was formed. After impregnating [Mg3.5Al]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 [Mg3.5Al]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.

Graphical abstractTrace amounts of Pt-doped Ni/Mg(Al)O catalysts prepared by sequential impregnation with Ni(II) and Pt(VI) starting from commercial Mg3.5–Al hydrotalcites (HTs) exhibited “intelligent” behavior, i.e., self-activation and self-regenerative activity in the DSS steam reforming of CH4. Mg(Al)O periclase that originated from Mg–Al HTs played an important role in the regenerative activity of the catalysts via reversible reduction–oxidation between Ni0 and Ni2+ on/in Mg(Al)O assisted by hydrogen spillover from Pt.Figure optionsDownload full-size imageDownload as PowerPoint slide