| Abstract
| - The activated adsorption of methane was investigated on two stepped Pt(355) and Pt(322) surfaces by time-dependent in situ high-resolution X-ray photoelectron spectroscopy (XPS) combined with a supersonicmolecular beam and was compared to corresponding results on Pt(111). Both stepped surfaces have fiveatom row wide (111) terraces but a different step orientation, namely, (111) and (100), respectively. Independentof the kinetic energy (0.45−0.83 eV) of impinging methane (CH4 or CD4), methyl is formed on all surfacesupon adsorption at 120 K. For the stepped surfaces, two different methyl species are identified from the XPspectra, which are attributed to adsorption at terrace sites and at step sites. The total initial sticking coefficients(for terrace + step sites) and the total coverages are very similar for all three surfaces. At low coverages,diffusion of methyl from the terraces to the steps is significantly stronger on Pt(355) than on Pt(322), and thestep saturation coverage is higher on Pt(355). The thermal evolution of methyl was also investigated by insitu temperature-programmed XPS. Overall, an enhanced reactivity toward dehydrogenation to methylidyneis found for both terrace and step sites on the stepped surfaces, with the (111) steps of Pt(355) exhibiting thehighest activity.
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