Formation of Reactive Clusters in Pd-Y Zeolite by Reduction-Reoxidation Treatment

Preparation of a finely dispersed Pd-Y zeolite has been investigated by temperature-programmed reduction (TPR) and extended X-ray absorption fine structure (EXAFS) techniques. Upon the treatment by a sequence of calcination, reduction, and reoxidation, the original Pd(NH3)42+ ions in the zeolite transformed to reactive species, which were reduced with hydrogen at room temperature and characterized as small PdO clusters of about 25 Pd atoms.

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The Determination of Interfacial Structure and Phase Transitions in Al/Cu and Al/Ni Interfaces by Means of Surface Extended X-Ray Absorption Fine Structure

MRS Proceedings ◽

10.1557/proc-238-211 ◽

1991 ◽

Vol 238 ◽

Author(s):

E. V. Barrera ◽

S. M. Heald

Keyword(s):

Fine Structure ◽

Room Temperature ◽

High Vacuum ◽

Ultra High Vacuum ◽

Interfacial Structure ◽

Reaction Products ◽

X Ray ◽

Absorption Fine ◽

Reaction Zones ◽

X Ray Absorption

ABSTRACTSurface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It became overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting to be CuAl2 and NiAl3 respectively. The results of this study showed that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10A reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30Å) and Al on Ni (60Å) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.

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Local structure determination of aluminum in Y zeolite: application of low energy X-ray absorption fine structure spectroscopy

Catalysis Letters ◽

10.1007/bf00814254 ◽

1994 ◽

Vol 29 (1-2) ◽

pp. 77-90 ◽

Cited By ~ 13

Author(s):

D. C. Koningsberger ◽

J. T. Miller

Keyword(s):

Fine Structure ◽

Structure Determination ◽

Local Structure ◽

Low Energy ◽

Y Zeolite ◽

X Ray ◽

Absorption Fine ◽

X Ray Absorption

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Unimportance of Siloxene in Luminescent Porous Silicon as Determined by Nexafs & Exafs

MRS Proceedings ◽

10.1557/proc-298-295 ◽

1993 ◽

Vol 298 ◽

Cited By ~ 1

Author(s):

S.L. Friedman ◽

M.A. Marcus ◽

D.L. Adler ◽

Y.-H. Xie ◽

T.D. Harris ◽

...

Keyword(s):

Fine Structure ◽

Porous Silicon ◽

Room Temperature ◽

Emission Spectra ◽

Porous Si ◽

X Ray ◽

Absorption Fine ◽

X Ray Absorption ◽

Room Temperature Luminescence ◽

Combined Data

AbstractNear-edge-- and extended--x-ray absorption fine structure measurements, as well as luminescence excitation and emission spectra, were obtained from samples of porous Si and siloxene. Contrary to a recently proposed explanation for the room temperature luminescence in porous Si, the combined data indicate that siloxene is not principally responsible for the observed effect.

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