Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 7: Heterogeneous Catalysis: Experiment

O 7.5: Vortrag

Montag, 12. März 2018, 11:30–11:45, MA 141

Operando X-ray absorption study on the influence of Ce³⁺ species on activity of Au/CeO₂ catalysts in the CO oxidation — •Joachim Bansmann, Ali Abel-Mageed, Gabriela Kucerova, Yuchen Wang, and R. Jürgen Behm — Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany

The catalytic activity and the deactivation behavior of Au/CeO₂ catalysts in the CO oxidation reaction depend strongly on the reductive or oxidative nature of the pretreatment [1]; oxidative pretreatments result in higher reaction rate. Detailed studies led to the following findings: Independent of the initial chemical state of the Au NPs directly after the pretreatments, the Au NPs always assumed a metallic state a few minutes after starting the reaction.
In this project, we investigated a possible influence of the chemical state of the ceria support (the ratio of Ce³⁺ to Ce⁴⁺ species) on the catalytic activity of Au/CeO₂ catalysts in the CO oxidation reaction by operando XAS measurements at the Ce L₃ edge. Directly after reductive pretreatments, the ceria support has a relatively high fraction of Ce³⁺ species (6-10%), whereas only 1% was found in case of an oxidative pretreatment. Independent of the initial state of the support, the amount of Ce³⁺ species decreased rapidly (within 10 min) during reaction (1%CO, 1%O₂, rest N₂) to values between about 1% or even less (oxidative pretreatment). Higher values are only observed in CO rich gas mixtures. These findings are discussed with respect to activity of the catalyst and the chemical state of the Au NPs.

[1] A. Abd-El Moemen et al., J. Catal. 341 (2016) 160