Scanning Tunneling Microscopy of the RuO2(110) Surface at Ambient Oxygen Pressure

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• 作者：M. Rö ; ssler ; S. G&uuml ; nther ; J. Wintterlin
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：February 8, 2007
• 年：2007
• 卷：111
• 期：5
• 页码：2242 - 2250
• 全文大小：570K
• 年卷期：v.111,no.5(February 8, 2007)
• ISSN：1932-7455

文摘

To test predictions about the activity of Ru catalysts the RuO₂(110) surface was investigated in an oxygenatmosphere at ambient pressure using scanning tunneling microscopy (STM). Epitaxial RuO₂(110) films weregrown on a Ru(0001) sample following an established preparation technique from ultrahigh vacuum (UHV)investigations. The sample was then exposed to 200 mbar of O₂ at 300 K, and STM images were takenduring exposure. The mesoscopic morphology of the film and the row structure of the RuO₂(110) surfaceknown from UHV were preserved. However, a 2-fold periodicity was observed along the [001] rows whichis inconsistent with the expected surface termination by O atoms bonded to the coordinatively unsaturatedsites of the RuO₂(110) surface. In addition, a second type of features that partially form clusters within theordered surface was observed. In a pure CO atmosphere at pressures of up to 21 mbar no atomic changes ofthis structure were observed, meaning that it does not contain O species that can react with CO. The newsurface phase was stable after removal of the O₂ atmosphere, so that it could be further characterized inUHV. Thermodesorption spectra showed strong desorption of CO₂ with peaks at 520 and 570 K but not theexpected recombinative desorption of O atoms from the coordinatively unsaturated sites. Photoelectronspectroscopy showed an O 1s state at 531.0 eV in addition to the bulk oxygen state of the RuO₂ film at 529.5eV. The most likely interpretation of the surface species in the oxygen atmosphere is a strongly bound carbonateformed by reaction of the surface with traces of CO or CO₂ in the O₂ atmosphere. The carbonate passivatesthe surface, leading to complete catalytic deactivation at 300 K. It is concluded that the established model forthe unusual activity of Ru catalysts, which is based on the unique chemical properties of the RuO₂(110)surface, cannot be extrapolated to ambient conditions for temperatures below the decomposition temperatureof the carbonate species.