Promoting effect of Rh, Pd and Pt noble metals to the Ni/Mg(Al)O catalysts for the DSS-like operation in CH₄ steam reforming

Effects of the additions of noble metal, i.e. Rh, Pd and Pt, on Ni/Mg(Al)O catalyst have been investigated for the daily start-up and shut-down (DSS) operation under steam purging in the steam reforming of CH₄. Mg_2.5(Ni_0.5)-Al hydrotalcite was prepared by coprecipitation and calcined to form Mg_2.5(Al,Ni_0.5)O periclase. When the powders of the periclase were dipped in an aqueous solution of the nitrate of Rh(III), Pd(II) or Pt(II), the hydrotaclite was reconstituted on the surface of Mg_2.5(Al,Ni_0.5)O particles due to a "memory effect," resulting in the formation of highly dispersed noble metal-Ni supported catalysts after the calcination followed by the reduction. The addition of noble metal on Ni resulted in a decrease in the reduction temperature of Ni²⁺ in Mg_2.5(Al,Ni_0.5)O periclase and an increase in the amount of H₂ uptake on the Ni⁰ over the Ni/Mg_2.5(Al)O catalyst. When Rh-, Pd- and Pt-Ni_0.5/Mg_2.5(Al)O catalysts were tested for the DSS-like operation under steam purging, the deactivation due to the Ni metal oxidation by steam was effectively suppressed by hydrogen spillover from noble metal to Ni. Especially, only 0.05 wt% of noble metal loading was enough to suppress effectively the deactivation during the DSS-like operation in the case of using both Rh and Pt.