Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 62: Metal Substrates: Adsorption of Inorganic Molecules
O 62.5: Talk
Thursday, February 28, 2008, 10:30–10:45, MA 042
Kinetic passivation of steps with sulfur and CO/S site exchange processes on stepped Pt surfaces — •Regine Streber1, Christian Papp1, Michael Peter Alexander Lorenz1, Andreas Bayer1, Reinhard Denecke2, and Hans-Peter Steinrück1 — 1Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen — 2Willhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Linnéstrasse 2, 04103 Leipzig
We studied the influence of sulfur on the adsorption and thermal evolution of CO on the stepped Pt(355) and Pt(322) surfaces by in-situ XPS. At low temperatures, we observe a passivation of the step sites for both surfaces, along with a decrease of the total CO coverage. Upon heating the CO covered surfaces a repopulation of the step sites with CO occurs at 185 K for Pt(355) and 240 K for Pt(322). For Pt(355), finally the same step coverage as for the clean surface is obtained, whereas for Pt(322) only half the value of the clean surface is found. This behavior is attributed to the S induced formation of double steps on Pt(322), which are stable in the investigated temperature range. From the lifting of the step passivation by sulfur upon heating for both surfaces we conclude that, under the experimental conditions applied, an occupation of steps sites by CO is energetically favored over occupation with S, with the CO-S site exchange process being kinetically hindered at low temperatures. The differences found for the two different step orientations are attributed to differences in the electronic structure and local adsorption sites. Supported by BMBF (05 ES3XBA/5).