Promoting effect of Rh, Pd and Pt noble metals to the Ni/Mg(Al)O catalysts for the DSS-like operation in CH 4 steam reforming

Abstract

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 CH 4. 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 Ni 2+ in Mg 2.5(Al,Ni 0.5)O periclase and an increase in the amount of H 2 uptake on the Ni 0 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.