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Mean Inner Potential of Nanostructured Noble Metal Catalysts - Pt/TiO2 Catalyst -

Published online by Cambridge University Press:  01 February 2011

S. Ichikawa ,
T. Akita ,
K. Okazaki ,
M. Okumura ,
K. Tanaka  and
M. Kohyama
S. Ichikawa
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST-Kansai), 1–8–31 Midorigaoka, Ikeda, OSAKA, 563–8577, Japan
T. Akita
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST-Kansai), 1–8–31 Midorigaoka, Ikeda, OSAKA, 563–8577, Japan
K. Okazaki
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST-Kansai), 1–8–31 Midorigaoka, Ikeda, OSAKA, 563–8577, Japan
M. Okumura
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST-Kansai), 1–8–31 Midorigaoka, Ikeda, OSAKA, 563–8577, Japan School of Science, Osaka University, 1–1 Machikaneyama, Toyonaka, OSAKA, 560–0043, Japan
K. Tanaka
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST-Kansai), 1–8–31 Midorigaoka, Ikeda, OSAKA, 563–8577, Japan
M. Kohyama
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST-Kansai), 1–8–31 Midorigaoka, Ikeda, OSAKA, 563–8577, Japan
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Abstract

Catalytic properties of noble metal catalysts are often caused by their nanostructures. Gold catalysts are typical cases. It is especially interesting that the catalytic property of gold suddenly changes to resemble that of platinum when the mean size of gold dispersed on certain oxides is <2nm. This phenomenon should be owing to the change of the local electronic structure of the gold particle or the interface between the gold and the oxides, however its detail has not been cleared yet. We measured the mean inner potential of gold particles supported on TiO2 using electron holography and HREM, and found that the mean inner potential of gold depend largely on the size of the gold particles. When the size is >5nm, the mean inner potential is the same as the reported values of bulk gold (experimental: 21–23V, calculated: 25–30V). When the size is <5nm, it begins to increase >30V, and it begins to increase suddenly >40V at the size <2nm. It indicates that the electronic structure of the gold particle varies from that of the bulk state as the size of the gold reduces due to the nano-size effect or the interaction at the interface, since the mean inner potential is sensitive to the electronic state of the outer valence electron. On the other hand, the behavior of the platinum catalysts is different from that of gold catalysts. When the size of the platinum particle on the TiO2 support is >1.5nm, the mean inner potential of platinum is the same as that of the bulk (∼25V). In case of the particle with the size <1.5nm, it begins to increase and the increase rate is lower than that of the gold particles with the size <2nm. It is suggested to be due to the difference of the interaction with TiO2.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 788: Symposium L – Continuous Nanophase and Nanostructured Materials , 2003 , L8.21
Copyright
Copyright © Materials Research Society 2004

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References

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