Coprecipitation versus chemical vapour deposition to prepare Rh/Nibimetallic catalysts

The Rh/Ni interaction in bimetallic Rh/Ni/Mg/Al hydrotalcite-type (HT) derived catalysts for the catalyticpartial oxidation (CPO) of CH4was studied modifying the preparation method. The conventional incor-poration of both Rh and Ni by coprecipitation (CP) of HT precursors was compared with the additionof Rh by chemical vapour deposition (CVD) to reduced Ni/Mg/Al HT-derived catalysts. Two Ni load-ings were selected (about 8 and 2 wt.%), whereas the Rh content was kept constant (0.18 wt.%). Ni- andRh-monometallic catalysts were prepared as reference materials.The addition of Rh resulted in an increase in Ni reducibility and dispersion for both CP and CVD cata-lysts. The Rh/Ni interaction was stronger in CP catalysts, while in CVD ones Rh overspread either on thesupport or Ni particles, with a preferential deposition on the latter. The Ni loading, regardless of the Rhincorporation method, was the main factor to determine the formation and growth of metallic particles.CO-DRIFTS spectra revealed that the dispersing and reducibility effect of Rh was more evident in thesamples with a lower Ni-loading.The small amount of Rh in the catalysts yielded to higher CH4conversions, especially in low Ni-containing catalysts wherein the Ni0oxidation was avoided. All the catalysts were activated duringcatalytic tests at high temperature by reduction of hardly reducible species. The strongest Rh/Ni inter-action in CP catalysts yielded to better performances with a lower carbon formation and high resistancetowards metallic particle sintering.