Are multiple oxygen species selective in ethylene epoxidation on silver?

The nature of the oxygen species active in ethylene epoxidation is a long-standing question. While the structure of the oxygen species that participates in total oxidation (nucleophilic oxygen) is known the atomic structure of the selective species (electrophilic oxygen) is still debated. Here, we u...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2018, Vol.9 (4), p.990-998
Main Authors: Carbonio, Emilia A, Rocha, Tulio C R, Klyushin, Alexander Yu, Píš, Igor, Magnano, Elena, Nappini, Silvia, Piccinin, Simone, Knop-Gericke, Axel, Schlögl, Robert, Jones, Travis E
Format: Article
Language:English
Subjects:
Atomic oxygen
Atomic structure
Epoxidation
Ethylene
Oxidation
X ray photoelectron spectroscopy
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Summary:The nature of the oxygen species active in ethylene epoxidation is a long-standing question. While the structure of the oxygen species that participates in total oxidation (nucleophilic oxygen) is known the atomic structure of the selective species (electrophilic oxygen) is still debated. Here, we use both and UHV X-ray Photoelectron Spectroscopy (XPS) to study the interaction of oxygen with a silver surface. We show experimental evidence that the unreconstructed adsorbed atomic oxygen (O ) often argued to be active in epoxidation has a binding energy (BE) ≤ 528 eV, showing a core-level shift to lower BE with respect to the O-reconstructions, as previously predicted by DFT. Thus, contrary to the frequent assignment, adsorbed atomic oxygen cannot account for the electrophilic oxygen species with an O 1s BE of 530-531 eV, thought to be the active species in ethylene epoxidation. Moreover, we show that O is present at very low O-coverages during XPS measurements and that it can be obtained at slightly higher coverages in UHV at low temperature. DFT calculations support that only low coverages of O are stable. The highly reactive species is titrated by background gases even at low temperature in UHV conditions. Our findings suggest that at least two different species could participate in the partial oxidation of ethylene on silver.
ISSN:2041-6520
2041-6539
DOI:10.1039/c7sc04728b