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Atomic and Electronic Structures of Nano-Interface In Au/TiO2 Catalyst - Electron Microscopic Approach -

Published online by Cambridge University Press:  11 February 2011

S. Ichikawa ,
K. Okazaki ,
T. Akita ,
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
K. Okazaki
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
M. Okumura
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST Kansai), 1–8–31 Midorigaoka, Ikeda, Osaka, 563–8577, 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

The size dependence of the catalytic property of the gold catalysts has been reported. It is especially interesting that the catalytic property of gold suddenly changes to show a platinum-like behavior when the mean size of gold is below 2nm. This phenomenon should be owing to the change of the electronic structure of the gold, however its detail has not been cleared yet. We investigated the size dependence of the mean inner potential of gold catalysts supported on TiO2, which is affected by the outer valence electron, using electron holography and high-resolution electron microscopy. We found the following tendency. When the size of the gold particle is over 5nm, the values of the mean inner potential are the same level as the reported experimental values of the bulk gold (21–23V) and the calculated values of the bulk gold (25–30V). When the size is below 5nm, the mean inner potential begins to increase over 30V, and it begins to increase suddenly over 40V at the size below about 2nm. It indicates that the electronic structure of the gold particles varies from that of the bulk state as the size of the gold particles reduces. Due to the size reduction, the volume fraction of the surface atoms and the interface atoms increases, e.g., almost half of the atoms locate on the surfaces or at the interface in case of the top half of the octahedron particle with the size 1.6nm. The surface dipole and the interface dipole should be formed owing to the electron out of the surface to the vacuum and the local charge transfer from the gold particles to the TiO2 surface. These dipole effects might be effective and one of the reasons for the increase of the mean inner potential of gold particles.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 738: Symposium G – Spatially Resolved Characterization of Local Phenomena in Materials and Nanostructures , 2002 , G13.11
Copyright
Copyright © Materials Research Society 2003

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