STUDY OF SILICA-SUPPORTED PTXNI1-X CATALYSTS BY ION-SCATTERING SPECTROSCOPY

As supported PtxNi1-x catalysts are used for hydrogenation reactions, it seemed necessary to assess the surface composition of the reduced s amples. To approach the usual reduction conditions we applied in situ reduction in a reaction chamber (1 mbar H-2 up to 500 degrees C) place d in ultra high vacuum recipient (UHV: 10(-9) to 2.10(-10) mbar). All ion scattering spectroscopy measurements were performed in UH V. Charg ing of the samples was avoided by electron bombardment (5 eV). The var iation of the surface composition was determined after subsequent sput tering, thermal treatment at 500 degrees C and during oxygen adsorptio n. A comparison with previous results of surface compositions of binar y alloys (polycrystalline foils [1, 2]and single crystals PtxNi1-x [3] ) is given.