Revealing the Dynamic Structure of Complex Solid Catalysts Using Modulated Excitation X-ray Diffraction

X‐ray diffraction (XRD) is typically silent towards information on low loadings of precious metals on solid catalysts because of their finely dispersed nature. When combined with a concentration modulation approach, time‐resolved high‐energy XRD is able to provide the detailed redox dynamics of pall...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2014-08, Vol.53 (34), p.8890-8894
Main Authors: Ferri, Davide, Newton, Mark A., Di Michiel, Marco, Chiarello, Gian Luca, Yoon, Songhak, Lu, Ye, Andrieux, Jérôme
Format: Article
Language:English
Subjects:
Carbon monoxide
Catalysis
Catalysts
ceria
Chemical Sciences
Diffraction
Dynamics
Fourier transforms
Material chemistry
Modulation
Palladium
time-resolved studies
X-ray diffraction
X-rays
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Summary:X‐ray diffraction (XRD) is typically silent towards information on low loadings of precious metals on solid catalysts because of their finely dispersed nature. When combined with a concentration modulation approach, time‐resolved high‐energy XRD is able to provide the detailed redox dynamics of palladium nanoparticles with a diameter of 2 nm in 2 wt % Pd/CZ (CZ=ceria–zirconia), which is a difficult sample for extended X‐ray absorption fine structure (EXAFS) measurements because of the cerium component. The temporal evolution of the Pd(111) and Ce(111) reflections together with surface information from synchronous diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements reveals that Ce maintains Pd oxidized in the CO pulse, whereas reduction is detected at the beginning of the O2 pulse. Oxygen is likely transferred from Pd to Ce3+ before the onset of Pd re‐oxidation. In this context, adsorbed carbonates appear to be the rate‐limiting species for re‐oxidation. Take a good look: By combining time‐resolved high‐energy X‐ray diffraction (XRD) with a modulation approach, the sensitivity can be increased so that subtle structural changes during a reaction become visible. Therefore, palladium particles with a diameter of approximately 2 nm could be detected by XRD, and their dynamic behavior under CO/O2 pulses was analyzed.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201403094