Synthesis of Ce and Pr-promoted Ni and Co catalysts from hydrotalcite type precursors by reconstruction method

Abstract

Catalysts were prepared from hydrotalcite type precursors using Ni, Co, and Ni–Co systems as active phases. Additionally Ce or Pr was incorporated as a promoter. The precursors were synthesized by the conventional co-precipitation method and the incorporation of Ce or Pr was carried out by reconstruction of the hydrotalcites in the presence of aqueous [Ce-EDTA]−1 or [Pr-EDTA]−1 chelates. The solids obtained were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), temperature programmed reduction (TPR), surface area, O2− and CO2− temperature programmed desorption (TPD) and their catalytic performance was evaluated in the ethanol oxidative steam reforming reaction. The analyses demonstrate that the hydrotalcite type precursors were synthesized effectively and their thermal decomposition generated mixed oxides with a periclase type structure and spinel phases for Co-containing catalysts. It was established that the mixed Ni–Co system exhibits better redox behavior and stronger basic centers in comparison with the Ni or Co isolated system. The promoting effect of Ce or Pr was confirmed by the increase of reducibility, the strength of the basic sites, and the stability of the metallic species within the solid solution. All of the catalysts were very active and selective in the oxidative steam reforming of ethanol. In particular, the presence of the promoters produces an increase in the hydrogen and CO2 selectivity. The catalysts' performance was found to be enhanced by the simultaneous presence of Ni and Co in the catalytic system, even without redox promoters.