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Influence of Steps on the Adsorption and Thermal Evolution of SO2 on Clean and Oxygen Precovered Pt Surfaces

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journal contribution
posted on 25.11.2010, 00:00 by R. Streber, C. Papp, M. P. A. Lorenz, O. Höfert, W. Zhao, S. Wickert, E. Darlatt, A. Bayer, R. Denecke, H.-P. Steinrück
We investigated the adsorption and reaction of SO2 on clean and oxygen precovered, flat, and regularly stepped Pt surfaces, Pt(111), Pt(322), and Pt(355) by in situ high resolution X-ray photoelectron spectroscopy. Induced by the steps and/or the coadsorbed oxygen, several new SO2 species are observed, in addition to the two known SO2 species on Pt(111). On all investigated surfaces, a hit and stick mechanism is found for the adsorption, and no diffusion from terrace to step sites occurs at low temperatures. For the oxygen free stepped surfaces, a higher reactivity toward SO2 dissociation/disproportionation is found compared to Pt(111). On all three oxygen precovered Pt surfaces some SO3 is already formed directly upon SO2 exposure at low temperatures. Heating of this mixed O/SOx layers first results in oxidation of more SO2 to SO3, and at higher temperatures in subsequent oxidation of SO3 to SO4, which finally decomposes above 450 K. The different reactions show a significant influence of the steps.