FTIR study of the oxidation reaction of CO with O-2 over bimetallic Pd-Rh/SiO2 catalysts in an oxidized state

CO species adsorbed on the surface of oxidized bimetallic Rh-Pd catalysts, prepared by coimpregnation and sequential impregnation methods, were analyz ed in situ by IR spectroscopy, during the reaction of CO with O-2 in an oxi dizing atmosphere. The results show that the two methods of impregnation le ad to the existence of oxidized Rh on the surface of the bimetallic catalys t, however, in the case of the sequential impregnation method, the Pd surfa ce is more reduced than in the case of catalysts prepared by coimpregnation . The simultaneous presence of reduced Pd and oxidized Rh that occurs in th e catalysts prepared by sequential impregnation allows the existence of a s ynergistic effect similar to that proposed in the literature for the Pt-Rh system. The lower degree of oxidation of the Pd in the catalysts prepared b y sequential impregnation, is mainly due to the fact that the Pd in these c atalysts comes from the organic precursor palladium acetylacetonate, while in the catalysts prepared by coimpregnation, the Pd comes from the precurso r PdCl2.