XPS STUDY OF PUMICE-SUPPORTED PALLADIUM AND PLATINUM CATALYSTS

An XPS study has been performed on samples of monometallic catalysts of palladium and platinum and on bimetallic Pd-Pt catalysts supported on pumice. A negative shift of about 0.5 eV in the Pd 3d and Pt 4f binding energies of the catalysts relative to the energies of the same levels in the pure metals suggested an increase in the electron density in both metals. A quantitative XPS analysis indicated that the supported metals did not modify the surface atomic composition of pumice. In the bimetallic catalysts the variation in the Pd 3d/Pd MNN intensity ratio over the different Pd/Pt atomic fractions has been attributed to surface segregation of the metal present in smaller amount.