A STUDY OF PT FILMS ON ZRO2(100)

The structure and CO adsorption properties of Pt films vapor deposited onto a ZrO2(100) crystal have been studied. Auger electron spectroscopy (AES) indicated that the growth of the film was almost two dimensional at 300 K; however, transmission electron microscopy (TEM) showed that the films formed particles upon exposure to air or mild heating above 350 K. Transmission electron diffraction (TED) indicated that these islands were oriented with respect to the underlying ZrO2 lattice, even for particles formed by heating to 850 K which were larger than 50 angstrom for deposition of 2 x 10(15) Pt/cm2. Temperature-programmed desorption (TPD) of CO from relatively high Pt coverages (> 1 x 10(15) Pt/cm2) and from Pt following particle formation showed desorption features at 400 and 510 K, similar to features found on Pt single crystals. For submonolayer quantities of Pt prior to annealing, a single CO desorption feature was observed at approximately 460 K, which is approximately 50 K lower than the peak temperature found for low Pt coverages on noninteracting supports. This shift appears to be due to interactions between Pt and the metal cations which are present on the ZrO2(100) surfaces. The implications of these results to catalyst support effects are discussed.