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Steiner, Carsten ; Gänzler, Andreas ; Zehentbauer, Melanie ; Hagen, Gunter ; Casapu, Maria ; Müller, Sabrina ; Grunwaldt, Jan-Dierk ; Moos, Ralf:
Oxidation state and dielectric properties of ceria-based catalysts by complementary microwave cavity perturbation and X-ray absorption spectroscopy measurements.
2018
Veranstaltung: CAPOC11 - 11th International Congress on Catalysis and Automotive Pollution Control
, Oct. 29 - 31, 2018
, Brussels, Belgium.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung
,
Poster
)
Abstract
The three-way catalytic converter (TWC) has become an integral part of the modern exhaust gas aftertreatment for gasoline engines. Some years ago, radio frequency technology was successfully tested for monitoring and controlling ceria based TWC oxygen storage by contactless measuring the dielectric catalyst properties inside a cavity resonator. Applying the cavity perturbation method, we present here results that have been specifically obtained for pure ceria, the oxygen storage component of three-way catalysts, and for differently prepared Pt-ceria model catalysts. The dielectric properties of the oxidized and (partially) reduced Pt-ceria and pure ceria powders were determined at 1.2 GHz between 250 °C and 550 °C. As the experiments show, the reduction of the material changes both, the polarization and also the occurring dielectric losses. The variations in the redox state of ceria were complementary probed by in situ X-ray absorption spectroscopicmeasurements conducted at the Ce L3-edge, which allowed to precisely determine the reduction and oxidation extent of ceria. The substantial improvement of the low-temperature reducibility of ceria in the presence of Pt was demonstrated. Time resolved data obtained during reducing/oxidizing cycles at 250 °C and 350 °C showed the faster and more pronounced reduction of ceria at higher temperature. Both methods proved to be valuable to provide insight into the oxygen storage and release process of ceria based materials, and capable to discriminate the impact of the noble metal or the ceria surface area in great detail, even under dynamic conditions, highly relevant for three-way catalysis.