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

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons54379

Greiner,  Mark
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
Heterogeneous Reactions, Max-Planck-Institute for Chemical Energy Conversion , Stiftstr. 34 - 36 45470 Mülheim an der Ruhr, Germany;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons183269

Cao,  Jing
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons135780

Jones,  Travis
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons205557

Skorupska,  Katarzyna
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons183245

Carbonio,  Emilia
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
Helmholz-Zentrum Berlin für Materialien und Energie;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons22243

Willinger,  Marc Georg
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons21743

Knop-Gericke,  Axel
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons22071

Schlögl,  Robert
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
Heterogeneous Reactions, Max-Planck-Institute for Chemical Energy Conversion , Stiftstr. 34 - 36 45470 Mülheim an der Ruhr, Germany;

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Zitation

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, 2286-2295. doi:10.1021/acscatal.7b04187.


Zitierlink: http://hdl.handle.net/21.11116/0000-0000-B5DB-D
Zusammenfassung
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.