X-Ray Absorption Spectroscopic Studies of Catalytic Materials

1988 ◽  
Vol 143 ◽  
Author(s):  
G. H. Via ◽  
J. H. Sinfelt ◽  
G. Meitzner ◽  
F. W. Lytle
Keyword(s):  
Fine Structure ◽  
Physical Environment ◽  
Bimetallic Catalysts ◽  
Spectroscopic Studies ◽  
Interatomic Distances ◽  
X Ray ◽  
Coordination Numbers ◽  
Supported Platinum ◽  
High Fraction ◽  
X Ray Absorption

AbstractX-ray absorption spectra (XAS) contain information in the LIII near-edge region on filling of the absorber d-band, and in the extended fine-structure region on the physical environment of the absorber. We report here an evaluation of the effect on platinum LIII edges of preparation in clusters with a high fraction of Pt atoms at the surface. We also report the effects on platinum and rhenium LIII edges from addition of copper. These effects are surprisingly small.We have also re-evaluated extended x-ray absorption fine-structure spectra (EXAFS) of platinum and rhenium in alumina-supported platinum-rhenium bimetallic catalysts. A novel feature of this new analysis was the requirement that interatomic distances, coordination numbers, and Debye-Waller type factors maintain certain physically necessary relationships among themselves. This procedure decreased the number of free variables and increased the amount of information returned by the analysis.

X-ray Absorption Fine Structure Spectroscopic Studies of Octakis(DMSO)lanthanoid(III) Complexes in Solution and in the Solid Iodides

2007 ◽  
Vol 46 (19) ◽  
pp. 7742-7748 ◽  
Author(s):  
Ingmar Persson ◽  
Emiliana Damian Risberg ◽  
Paola D'Angelo ◽  
Simone De Panfilis ◽  
Magnus Sandström ◽  
...  
Keyword(s):  
Fine Structure ◽  
Spectroscopic Studies ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

scholarly journals X-Ray Absorption Spectroscopy from H-Passivated Porous Si and Oxidized Si Nanocrystals

1994 ◽  
Vol 375 ◽  
Author(s):  
S. Schuppler ◽  
S. L. Friedman ◽  
M. A. Marcus ◽  
D. L. Adler ◽  
Y.-H. Xie ◽  
...  
Keyword(s):  
Fine Structure ◽  
Quantum Confinement ◽  
Ir Absorption ◽  
X Ray ◽  
Coordination Numbers ◽  
Absorption Fine ◽  
Visible Luminescence ◽  
Si Nanocrystals ◽  
Wide Range ◽  
X Ray Absorption

AbstractQuantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The H/Si ratios, as large as 1.2, were independently confirmed by ir-absorption and α-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 Å. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.

EXAFS Study of Rutile and Anatase

1981 ◽  
Vol 36 (11) ◽  
pp. 1192-1195 ◽  
Author(s):  
G. Vlaic ◽  
J. C. J. Bart ◽  
W. Cavigiolo ◽  
S. Mobilio ◽  
G. Navarra
Keyword(s):  
Fine Structure ◽  
Data Analysis ◽  
Curve Fitting ◽  
Structure Study ◽  
Fourier Methods ◽  
X Ray ◽  
Coordination Numbers ◽  
Exafs Study ◽  
Cation Coordination ◽  
X Ray Absorption

Two crystallographic forms of TiO2 (rutile and anatase) were subject to an extended x-ray absorption fine structure study at the K threshold of titanium. Data analysis was carried out by Fourier methods and curve fitting techniques. Using the theoretical phases, Ti-O bond distances of 1.93(1) Å were derived both for rutile and anatase, as compared to the crystallographic values of 1.948 - 1.980(1) Å (rutile) and 1.934-1.980(1) Å (anatase). The ratio of the cation coordination numbers Nr/Na = 1.07 is close to the theoretical value.

Ab Initio XAFS and XANES Standards

1993 ◽  
Vol 307 ◽  
Author(s):  
J. J. Rehr ◽  
S. I. Zabinsky ◽  
R. C. Albers
Keyword(s):  
Fine Structure ◽  
Ab Initio ◽  
Multiple Scattering ◽  
State Of The Art ◽  
Experimental Measurements ◽  
Edge Structure ◽  
X Ray ◽  
Coordination Numbers ◽  
X Ray Absorption ◽  
Better Than

ABSTRACTAb initio x-ray-absorption fine structure (XAFS) and x-ray-absorption near edge structure (XANES) standards are developed for molecules and solids. These standard XAFS spectra are obtained from ab initio XAFS calculations, using an automated code, FEFF, which we have extended to include multiple-scattering (MS) and XANES calculations. Our treatment is based on state-of-the-art curved-wave MS theory. Sample results are presented and compared with experiment. We find that these theoretical standards are comparable with experimental measurements, yielding distance determinations better than 0.02 Å and coordination numbers better than 20%. Our approach also gives a new MS interpretation of the σ* shape-resonances in XANES.

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