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Redox Behavior Below 1000K of Pt-Impregnated CeO2-ZrO2 Solid Solutions: An In-Situ Neutron Diffraction Study

Published online by Cambridge University Press:  10 February 2011

C.-K. Loong ,
S. M. Short ,
M. Ozawa  and
S. Suzuki
C.-K. Loong
Affiliation:
Argonne National Laboratory, Argonne, IL 60439, U. S. A.
S. M. Short
Affiliation:
Argonne National Laboratory, Argonne, IL 60439, U. S. A.
M. Ozawa
Affiliation:
Nagoya Institute of Technology, Tajimi, Gifu, 507, Japan.
S. Suzuki
Affiliation:
Nagoya Institute of Technology, Tajimi, Gifu, 507, Japan.
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Abstract

The Ce3+ ↔ Ce4+ redox process in automotive three-way catalysts such as Ce-ZrO2/Pt provides an essential mechanism to oxygen storage/release under dynamic air-to-fuel ratio cycling. Such a function requires a metal-support interaction which is not completely understood. We have carried out an in-situ neutron powder diffraction study to monitor the crystal structures (a mixture of a major tetragonal and a minor monoclinic phase) of 10mol% Ce-doped ZrO2 with and without Pt (1wt%) impregnation under oxidizing and reducing conditions over the temperature range of 25°-700°C. The samples were heated first in flowing 2%O2/Ar from room temperature to 400°C and then in 1%CO/Ar to about 700°C. A discontinued increase of the tetragonal unit-cell volume, a decrease of tetragonality (c/a), and a change of color from light yellow to gray when changing from oxidizing to reducing atmosphere were observed only in the sample containing Pt. This result supports the model which assumes the formation of oxygen vacancies initially near the Pt atoms. As more Ce ions are reduced from 4+ to 3+ oxidation states at high temperatures, oxygen vacancies migrate to the bulk of the oxide particles.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 497: Symposium Z – Recent Advances in Catalytic Materials , 1997 , 65
Copyright
Copyright © Materials Research Society 1998

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References

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