Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 28: Heterogeneous catalysis II
O 28.1: Vortrag
Dienstag, 27. März 2012, 10:30–10:45, MA 042
Ethylene Oxide Formation over Ag: Investigation of the "electrophilic" Oxygen on Ag(111) — •Sebastian Böcklein1, Miguel À. Niño2, Tevfik O. Menteş2, Andrea Locatelli2, Sebastian Günther3, and Joost Wintterlin1 — 1Ludwig-Maximilians-Universität München, Germany — 2Sincrotrone Trieste S.C.p.A., Trieste, Italy — 3Technische Universität München, Germany
The understanding of the ethylene oxide formation crucially depends on the active oxygen species on the Ag catalyst. We have used x-ray photoelectron spectroscopy (XPS), temperature-programmed desorption and reaction (TPD and TPR), low-energy electron- as well as photo electron emission microscopy (LEEM / XPEEM) and scanning tunneling microscopy (STM) to identify and characterize O species on Ag(111). In addition to the (4×4)O phase (O 1s BE 528.3 eV) assigned to "nucleophilic" oxygen, the "electrophilic" oxygen (most likely the active species for the partial oxidation) was prepared under UHV conditions applying a special treatment using NO2. The latter phase has previously only been prepared by extremely high O2 exposures. XPS reveals two species (O 1s BE 530.2 and 530.7 eV). STM and LEED show a (7× √3)rect structure, which is connected with a massive change of the surface morphology. STM and TPR experiments show that this phase reacts with ethylene to give ethylene oxide. In situ STM experiments, performed under reaction conditions in the mbar regime, show structures and surface morphology changes that had before been observed in UHV experiments.