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  Phase Coexistence of Multiple Copper Oxides on AgCu Catalysts during Ethylene Epoxidation

Greiner, M., Cao, J., Jones, T., Beeg, S., Skorupska, K., Carbonio, E., et al. (2018). Phase Coexistence of Multiple Copper Oxides on AgCu Catalysts during Ethylene Epoxidation. ACS Catalysis, 8(3), 2286-2295. doi:10.1021/acscatal.7b04187.

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 Creators:
Greiner, Mark1, 2, Author              
Cao, Jing1, Author              
Jones, Travis1, Author              
Beeg, Sebastian2, Author
Skorupska, Katarzyna1, Author              
Carbonio, Emilia1, 3, Author              
Sezen, Hikmet3, 4, Author
Amati, Matteo4, Author
Gregoratti, Luca4, Author
Willinger, Marc Georg1, Author              
Knop-Gericke, Axel1, Author              
Schlögl, Robert1, 2, Author              
Affiliations:
1Inorganic Chemistry, Fritz Haber Institute, Max Planck Society, ou_24023              
2Research Department Schlögl, Max Planck Institute for Chemical Energy Conversion, Max Planck Society, ou_3023874              
3Helmholz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany, ou_persistent22              
4Elettra-Sincrotrone Trieste, Strada Statale 14, 34149 Basovizza, Italy, ou_persistent22              

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 Abstract: Alloy catalysts under reaction conditions are complex entities. In oxidizing atmospheres, multiple phases can coexist on a catalyst’s surface as a result of phase segregation and preferential oxidation. Such a scenario can result in unusual substoichiometric and metastable phases that could play important roles in catalytic processes. For instance, AgCu alloys—known to exhibit enhanced epoxide selectivity in partial oxidation of ethylene—form an oxide-like surface structure under reaction conditions. Under these conditions, copper oxides are stable, while silver oxides are not. Consequently, copper segregates to the alloy’s surface and forms an oxide overlayer. Little is known about the structure or function of such overlayers, and it is unknown whether they play an active role in the catalyst’s enhanced selectivity. In order to develop a clearer picture of such catalysts, the current work utilizes several in situ spectroscopic and microscopic techniques to examine the copper oxide phases that form when AgCu is exposed to epoxidation conditions. It is found that several forms of oxidic Cu coexist simultaneously on the active catalyst’s surface, namely, CuO, Cu2O, and some previously unreported form of oxidized Cu, referred to here as CuxOy. Online product analysis, performed during the in situ spectroscopic measurements, shows that increased epoxide selectivity is correlated with the presence of mixed copper oxidation states and the presence of the CuxOy species. These results support previous theoretical predictions that oxidic copper overlayers on silver play an active role in epoxidation. These results furthermore emphasize the need for in situ spectromicroscopic methods to understand the complexity of alloy catalysts.

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Language(s): eng - English
 Dates: 2018-02-012017-12-062018-02-03
 Publication Status: Published online
 Pages: 10
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/acscatal.7b04187
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Title: ACS Catalysis
  Abbreviation : ACS Catal.
Source Genre: Journal
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Publ. Info: Washington, DC : ACS
Pages: 10 Volume / Issue: 8 (3) Sequence Number: - Start / End Page: 2286 - 2295 Identifier: Other: 2155-5435
CoNE: https://pure.mpg.de/cone/journals/resource/2155-5435