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          Institute: Fritz-Haber-Institut     Collection: Inorganic Chemistry     Display Documents



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ID: 315345.0, Fritz-Haber-Institut / Inorganic Chemistry
High-pressure STM of the interaction of oxygen with Ag(111)
Authors:Reichelt, Robert; Günther, Sebastian; Rößler, Mario W.; Wintterlin, Joost; Kubias, Bernd; Jacobi, Britta; Schlögl, Robert
Language:English
Research Context:oxidation
Date of Publication (YYYY-MM-DD):2007
Title of Journal:Physical Chemistry Chemical Physics
Journal Abbrev.:PCCP
Volume:9
Issue / Number:27
Start Page:3590
End Page:3599
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:To identify surface phases that could play a role for the epoxidation of ethylene on Ag catalysts we have studied the interaction of Ag(111) with O2 at elevated pressures. Experiments were performed using high-pressure scanning tunneling microscopy (STM) at temperatures between 450 and 480 K and O2 pressures in the mbar range. Below p(O2) 1 mbar the surface largely showed the structure of bare Ag(111). At p(O2) above 1 mbar the (4 × 4)O structure and the closely related (4 × 5 3)rect structure were observed. The findings confirm theoretical predictions that the (4 × 4)O structure is thermodynamically stable at the oxygen partial pressure of the industrial ethylene oxide synthesis. However, in other experiments only a rough, disordered structure was observed. The difference is caused by the chemical state of the STM cell that depends on the pretreatment and on previous experiments. The surface was further analyzed by X-ray photoelectron spectroscopy (XPS). Although these measurements were performed after sample transfer to ultra-high vacuum (UHV), so that the surface composition was modified, the two surface states could still be identified by the presence of carbonate or a carbonaceous species, and by the absence or presence of a high-binding energy oxygen species, respectively. It turns out that the (4 × 4)O structure only forms under extremely clean conditions, indicating that the (4 × 4)O phase and similar oxygen-induced reconstructions of the Ag(111) surface are chemically unstable. Chemical reactions at the inner surfaces of the STM cell also complicate the detection of the catalytic formation of ethylene oxide.
External Publication Status:published
Document Type:Article
Communicated by:Robert Schlögl
Affiliations:Fritz-Haber-Institut/Inorganic Chemistry/Microstructure
Fritz-Haber-Institut/Inorganic Chemistry/Inorganic Chemistry
Identifiers:URL:http://dx.doi.org/10.1039/b700432j [only subscribers]
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