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Title: EXAFS Characterization of Dendrimer-PT Nanocomposites Used for the Preparation of Pt/gamma-Al2O3 Catalysts

Abstract

No abstract prepared.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930161
Report Number(s):
BNL-80819-2008-JA
TRN: US200822%%1211
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry B; Journal Volume: 110
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATALYSTS; CHEMICAL PREPARATION; PLATINUM; CATALYST SUPPORTS; ALUMINIUM OXIDES; COMPOSITE MATERIALS; X-RAY SPECTROSCOPY; ABSORPTION SPECTROSCOPY; national synchrotron light source

Citation Formats

Alexeev,O., Siani, A., Lafaye, G., Williams, C., Ploehn, H., and Amiridis, M. EXAFS Characterization of Dendrimer-PT Nanocomposites Used for the Preparation of Pt/gamma-Al2O3 Catalysts. United States: N. p., 2006. Web. doi:10.1021/jp063787+.
Alexeev,O., Siani, A., Lafaye, G., Williams, C., Ploehn, H., & Amiridis, M. EXAFS Characterization of Dendrimer-PT Nanocomposites Used for the Preparation of Pt/gamma-Al2O3 Catalysts. United States. doi:10.1021/jp063787+.
Alexeev,O., Siani, A., Lafaye, G., Williams, C., Ploehn, H., and Amiridis, M. Sun . "EXAFS Characterization of Dendrimer-PT Nanocomposites Used for the Preparation of Pt/gamma-Al2O3 Catalysts". United States. doi:10.1021/jp063787+.
@article{osti_930161,
title = {EXAFS Characterization of Dendrimer-PT Nanocomposites Used for the Preparation of Pt/gamma-Al2O3 Catalysts},
author = {Alexeev,O. and Siani, A. and Lafaye, G. and Williams, C. and Ploehn, H. and Amiridis, M.},
abstractNote = {No abstract prepared.},
doi = {10.1021/jp063787+},
journal = {Journal of Physical Chemistry B},
number = ,
volume = 110,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • No abstract prepared.
  • The various steps involved in the preparation of a Pt/{gamma}-Al2O3 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 (H2PtCl6 and K2PtCl4) were partially replaced by aquo ligands upon hydrolysis to form [PtCl3(H2O)3]+ and [PtCl2(H2O)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 tomore » Pt, indicating that the former plays the role of a ligand. Following treatment of the H2PtCl6/G4OH and K2PtCl4/G4OH composites with NaBH4, 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 H2, 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 H2 treatment. Formation of Pt nanoparticles with an average diameter of approximately 10 A was finally observed after the deposition of H2PtCl6/G4OH on {gamma}-Al2O3 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 O2/H2 led to further sintering.« less
  • Highly dispersed Pt catalysts were prepared by deposition of Pt{sub 4} and Pt{sub 6} clusters, initially formed in unprotected and poly(vinyl alcohol) (PVA)-protected colloidal Pt suspensions, onto a {gamma}-Al{sub 2}O{sub 3} surface. These catalysts were characterized by extended X-ray absorption fine structure (EXAFS) and Fourier transform infrared (FTIR) spectroscopies. The EXAFS results indicate that the supported Pt species formed were very similar in structure to those of the original clusters in the corresponding colloidal suspensions. The FTIR results further indicate that the {gamma}-Al{sub 2}O{sub 3}-supported Pt{sub 4} clusters have significantly lower chemisorptive properties compared with larger supported Pt nanoparticles; nevertheless,more » the Pt{sub 4}/{gamma}-Al{sub 2}O{sub 3} sample was active for the oxidation of CO with no need for additional activation treatment. In fact, treatment of this sample with H{sub 2} at 150--200 {sup o}C led to the formation of Pt aggregates with sizes of 1.0--1.6 nm, demonstrating that the surface Pt4 species readily sintered in this temperature range under reducing conditions.« less
  • No abstract prepared.
  • Reverse micelle synthesis was used to improve the nanoparticle size uniformity of bimetallic Pt/Ni nanoparticles supported on {gamma}-Al{sub 2}O{sub 3}. Two impregnation methods were investigated to optimize the use of the micelle method: (1) step-impregnation, where Ni nanoparticles were chemically reduced in microemulsion and then supported, followed by Pt deposition using incipient wetness impregnation, and (2) co-impregnation, where Ni and Pt were chemically reduced simultaneously in microemulsion and then supported. Transmission electron microscopy (TEM) was used to characterize the particle size distribution. Atomic absorption spectroscopy (AAS) was used to perform elemental analysis of bimetallic catalysts. Extended X-ray absorption fine structuremore » (EXAFS) measurements were utilized to confirm the formation of the Pt-Ni bimetallic bond in the step-impregnated catalyst. CO pulse chemisorption and Fourier transform infrared spectroscopy (FTIR) studies of 1,3-butadiene hydrogenation in a batch reactor were performed to determine the catalytic activity. Step-impregnated Pt/Ni catalyst demonstrated enhanced hydrogenation activity over the parent monometallic Pt and Ni catalysts due to bimetallic bond formation. The catalyst synthesized using co-impregnation showed no enhanced activity, behaving similarly to monometallic Ni. Overall, our results indicate that reverse micelle synthesis combined with incipient wetness impregnation produced small, uniform nanoparticles with bimetallic bonds that enhanced hydrogenation activity.« less