Issue 4, 2018

Are multiple oxygen species selective in ethylene epoxidation on silver?

Abstract

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 in situ 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 (Oads) 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 Oads is present at very low O-coverages during in situ 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 Oads 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.

Graphical abstract: Are multiple oxygen species selective in ethylene epoxidation on silver?

Supplementary files

Article information

Article type
Edge Article
Submitted
01 Nov 2017
Accepted
26 Nov 2017
First published
27 Nov 2017
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2018,9, 990-998

Are multiple oxygen species selective in ethylene epoxidation on silver?

E. A. Carbonio, T. C. R. Rocha, A. Yu. Klyushin, I. Píš, E. Magnano, S. Nappini, S. Piccinin, A. Knop-Gericke, R. Schlögl and T. E. Jones, Chem. Sci., 2018, 9, 990 DOI: 10.1039/C7SC04728B

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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