Abstract
Oxygen adsorption and desorption were studied on the Pt(111) and Pt(S)-12(111) × (111) surfaces over the 100 to 1300 K temperature range using thermal desorption. Auger electron spectroscopy, X-ray photoemission spectroscopy and low energy electron diffraction. Isotope exchange experiments indicate that the low temperature desorption peak (150 K) results from molecular adsorption while the high temperature peak (400–600 K) results from atomic adsorption. Chemical titration experiments indicate that little or no dissociation of adsorbed molecular oxygen occurs at 100 K, that is, oxygen dissociation on platinum is activated. Adsorption into the molecular state is not activated as indicated by large initial sticking coefficients observed at 100 K. Molecular oxygen also adsorbs on these surfaces with preadsorbed (2 × 2) atomic oxygen overlayers. Adsorption of oxygen above 170 K proceeds rapidly to a coverage of about 3.8 × 10 14 oxygen atoms cm 2 (the (2 × 2)O structure). Further oxygen can be adsorbed up to a coverage of about 8 × 10 14 atoms cm 2 using extended temperature cycling around 150 K or external atomization. The kinetics of desorption for both the low temperature and high temperature peaks are complex, making extraction of detailed information difficult. Adsorption of molecular oxygen on top of a previously formed (2 × 2)O structure results in simple desorption kinetics due to the drastically reduced probability of atomization during desorption.
Published Version
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