EXAFS Characterization of Dendrimer-Derived Pt/Gamma-Al(2)O(3)
The various steps involved in the preparation of a Pt/{gamma}-Al{sub 2}O{sub 3} material using hydroxyl-terminated generation four (G4OH) PAMAM dendrimers as templates were monitored by EXAFS. The results indicate that Cl ligands in the Pt precursors (H{sub 2}PtCl{sub 6} and K{sub 2}PtCl{sub 4}) were partially replaced by aquo ligands upon hydrolysis to form [PtCl{sub 3}(H{sub 2}O){sub 3}]{sup +} and [PtCl{sub 2}(H{sub 2}O){sub 2}] species. After interaction of such species with G4OH, Cl ligands from the first coordination shell of Pt were further replaced by nitrogen atoms from the dendrimer interior, indicating the complexation of Pt with the dendrimer. This process was accompanied by a transfer of the electron density from the dendrimer to Pt, indicating that the former plays the role of a ligand. Following treatment of the H{sub 2}PtCl{sub 6}/G4OH and K{sub 2}PtCl{sub 4}/G4OH composites with NaBH{sub 4}, no substantial changes were detecteded in the electronic or coordination environment of Pt, and no formation of metal nanoparticles was observed. However, when the reduction treatment was performed with H{sub 2}, the formation of extremely small Pt clusters incorporating no more than 4 Pt atoms was observed. These Pt species remained strongly bonded to the dendrimer and their nuclearity depends on the length of the H{sub 2} treatment. Formation of Pt nanoparticles with an average diameter of approximately 10 {angstrom} was finally observed after the deposition of H{sub 2}PtCl{sub 6}/G4OH on {gamma}-Al{sub 2}O{sub 3} and drying, suggesting that their formation may be related to the collapse of the dendrimer structure. The Pt nanoparticles formed appear to have high mobility, since subsequent thermal treatment in O{sub 2}/H{sub 2} led to further sintering.
- Research Organization:
- Stanford Linear Accelerator Center (SLAC)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 953866
- Report Number(s):
- SLAC-REPRINT-2009-525
- Journal Information:
- AIP Conf.Proc.882:737,2007, Journal Name: AIP Conf.Proc.882:737,2007
- Country of Publication:
- United States
- Language:
- English
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