Thermal Stability of Supported Noble Metal Nanoclusters
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0915-R06-18
Thermal Stability of Supported Noble Metal Nanoclusters
Galif Kutluk1, Shinya Yagi2, Hirosuke Sumida3, Hirofumi Namatame1, and Masaki Taniguchi1 1
Hiroshima Synchrotron Radition Center, Hiroshima University, 2-313 Kagamiyama,
Higashi-Hiroshima, Hiroshima, 739-0046, Japan 2
School of engineering, Nagoya University, Nagoya, 464-8603, Japan
3
Technical Reserch Center, Mazda Motor Co., Fuchu, Hiroshima, 730-8670, Japan
ABSTRACT Highly dispersive and size controlled Pd and Pt nanoclusters have been synthesized by gas condensation and Arc plasma source. The morphology, crystallographic structures, electronic structure and the temperature dependence of chemical states of nanocluster were investigated by using TEM, AFM, EXAFS and XPS, respectively. The results show that non-passivized Pd nanoclusters with the size of 1.5~ 5.7nm are consisted with pure Pd core covered by highly oxidized PdO2 thin layer. The dioxide state PdO2 layers start to converting to Pd at 120˚C and vanishing at 180˚C in a reduction atmosphere. INTRODUTION Metallic nanostructures have been interested from both industrial and scientific communities due to their possible applications in devices and fundamental questions they present. They show very catalytic activity and Coulomb blockades which are not found in either bulk or molecular/atomic systems. Since nano-particle has the large fraction of low coordinated atoms at its surface and the confinement of electrons to a rather small volume. Nanoclusters ((nano-particles) with the size of 1-3 nm in diameter, are expected to have strong size-dependent properties (for example, geometric and electronic structure, magnetism, binding energy, melting temperature)[1]. Traditionally there are two methods in synthesizing metallic nano-cluster: one is the colloidal chemistry (wet process) a powerful method for performing the metal nano-cluster with precisely size controllability [2]. However, the surface of the nano-cluster is problematic; it is usually encapsulated by ligand shell (surfactant), which prevents the individual nano-cluster agglomeration with each other in a solvent. The ligand shell also prevents to obtain information about the geometric and electronic structures of nano-cluster. The second method is based on the evaporation of a metal to a substrate in an ultra high vacuum condition [3]. It is a useful method for obtaining high purity metal nano-cluster, however, it appears to be not convenient for controlling the cluster size. Recent developments in synthesizing metallic nano-cluster suggest that the Gas phase condensation (inert gas aggregation) combined with Arc plasma method is not only convenient in
synthesizing metal nano-cluster with cleaner surface but also is suitable for size controlling [4]. In addition, this method also shows advantage in making cluster with a simple shape in three dimensional shape (for example a spherical) on a supporting material. Metal cluster dispersed on planer oxide supporter has been used extensively as the model catalysts [6]. The catalytic
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