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 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. (C) 2006 Elsevier B.V. All rights reserved.