STUDY OF CO CHEMISORPTION ON POLYCRYSTALLINE PT

The chemisorption of CO on a sputtered and annealed polycrystalline Pt surface has been examined using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). Data obtained from an isotop ic TPD experiment indicate that adsorption is molecular with no detect able CO dissociation. ISS data demonstrate that the CO bonds to the Pt through the C with the O pointing away from the surface and that abou t 80% of the Pt surface is covered at saturation based on the relative sizes of the ISS Pt peak heights obtained from the clean and CO-satur ated surfaces. Coverage versus exposure plots have been determined fro m both the ISS and TPD data, and the agreement is generally good. The sticking coefficient is close to 1 up to 0=0.5 and than falls rapidly with increasing exposure to the saturation exposure of 90 L. The Kisli uk adsorption model, which assumes adsorption at a single type of site , is able to provide a good fit of the ISS uptake data but is not as s uccessful in fitting the TPD uptake data.