METAL-SUPPORT INTERACTION IN PT/C CATALYSTS, INFLUENCE OF THE SUPPORT SURFACE-CHEMISTRY AND THE METAL PRECURSOR

The influence of support surface chemistry and metal precursor species on the properties of Pt/C catalysts has been analyzed. The char of a phenolformaldehyde polymer is the carbon source for obtaining four different supports: three with different degree of surface oxidation and another one modified by ion-exchanged calcium. These supports have been impregnated with aqueous solutions of two platinum precursors with different ionic character: chloroplatinic acid and tetraaminplatinum chloride. The study of the system consists of a preliminary characterization of the supports (surface chemistry and textural properties), an EXAFS analysis of the fresh impregnated catalysts and the determination of platinum dispersion. The platinum precursor-support interaction, established after the impregnation step, and the platinum precursor distribution have been related to the surface chemistry of the supports and the platinum precursor used. The effect of these parameters in the final metal dispersion has also been investigated. The results obtained show that the degree of support surface oxidation has a strong influence on the distribution of the metal precursor on the support and, consequently, on the final platinum dispersion. The surface oxidation of the supports seems to have a negative effect on the platinum dispersion, independently of the platinum precursor used. Thus, the lower the number of surface oxygen complexes, the higher the metal dispersion. The reduction of precursor H2PtCl6 by interaction with the carbon has also been found to depend on the surface chemistry of the supports.