"Intelligent" reforming catalysts: Trace noble metal-doped Ni/Mg(Al)O derived from hydrotalcites

Trace amounts of noble metal-doped Ni/Mg(Al)O catalysts were prepared starting from Mg-Al hydrotalcites (HTs) and tested in daily start-up and shut-down (DSS) operation of steam reforming (SR) of methane or partial oxidation (PO) of propane. Although Ni/Mg(Al)O catalysts prepared from Mg(Ni)-Al HT exhibited high and stable activity in stationary SR, PO and dry reforming of methane and propane, the Ni/Mg(Al)O catalysts were drastically deactivated due to Ni oxidation by steam as purge gas when they were applied in DSS SR of methane. Such deactivation was effectively suppressed by doping trace amounts of noble metal on the catalysts by using a "memory effect" of HTs. Moreover, the noble metal-doped Ni/Mg(Al)O catalysts exhibited "intelligent" catalytic behaviors, i.e., self-activation and self-regenerative activity, leading to high and sustainable activity during DSS operation. Pt was the most effective among noble metals tested. The self-activation Occurred by the reduction of Ni(2+) in Mg(Ni,Al)O periclase to Ni(0) assisted by hydrogen spillover from Pt (or Pt-Ni alloy). The self-regenerative activity was accomplished by self-redispersion of active Ni(0) particles due to a reversible reduction-oxidation movement of Ni between the outside and the inside of the Mg(Al)O periclase crystal, surface Ni(0) was oxidized to Ni(2+) by steam and incorporated into Mg(Ni(2+),Al)O periclase, whereas the Ni(2+) in the periclase was reduced to Ni(0) by the hydrogen spillover and appeared as the fine Ni(0) particles on the catalyst surface. Further a "green" preparation of the Pt/Ni/[Mg(3.5)Al]O catalysts was accomplished starting from commercial Mg(3.5)-Al HT by calcination, followed by sequential impregnation of Ni and Pt.