The Effects of Platinum or Rhodium on the Structures and Properties of Co/CeO₂ Catalyst

Co-Pt/CeO₂ and Co-Rh/CeO₂ （Co₃O₄/CeO₂=8%,M/CeO₂=0.1%,M=Pt or Rh） catalysts were prepared by successive wetness impregnation method. The results of activity measurements show that there exists catalytic synergy effect between noble metals and cobalt. For CO oxidation, the synergy effect between Pt and Co is more obvious than that between Rh and Co. But for the selective catalytic reduction of NO by CH₄ in the presence of exces soxygen, the synergy effect between Rh and Co is more obvious. Both the results of XPS and EXAFS indicate that all cobalt in Co/CeO₂, Co-Pt/CeO₂ and Co-Rh/CeO₂ exists in metallic state which is so highly dispersed that it is difficult to detect by XRD. The increase of cobalt percentage on the catalyst surface and the decrease of Co-Co shell coordination number show that the addition of the small amount of platinum or rhodium to Co/CeO₂ has improved the dispersion of cobalt phase on the surface of Co/CeO₂. The effects of the small amount of Pt or Rh on Co/CeO₂ are discussed.