EXAFS spectrum

EXAFS spectra of platinum metal, having a face-centred cubic crystal stmcture, have been obtained at 300 K and 673 K. Explain what qualitative differences you might expect. How many nearest-neighbour atoms are there in this stmcture Illustrate your answer with a diagram. 

Figure 2 Surface EXAFS spectra above the Pd L edge for a 1.5 monolayer evaporated film of Pd on Sid 11) and for bulk palladium ailicide, Pd2Si and metallic Pd.

Measuring EXAFS spectra In general, transmission EXAFS can be used, provided that the concentration of the element to be investigated is sufficiently high. The sample is placed between two ionization chambers, the signals of which are proportional to the incident intensity Iq and the transmitted intensity through the sample 7f The transmission of the sample is dependent on the thickness of the sample X and on the absorption coefficient, //, in a Beer-Lambert relationship ... 

Figure 3.77 EXAFS spectra of the isomers of Pt(bipy)(NCS)2. (Reprinted with permission from Inorg. Chem., 1992, 31, 1752. Copyright (1992) American Chemical Society.)...

X-ray absorption spectroscopy has been performed on the isolated Rieske protein from bovine heart mitochondrial bc complex 69) as well as on the Rieske-type cluster in Burkholderia cepacia phthalate dioxygenase (PDO) (72). The analysis performed by Powers et al. 69) was significantly hampered by the fact that the presence of two histidine ligands was not fully recognized therefore, only the results obtained with the dioxygenase where the mononuclear iron has been depleted will be considered here. Table VII gives a comparison of the distances obtained from the fit of the EXAFS spectra assuming an idealized Rieske model and of the distances in the crystal structures... 

The Mo K-edge EXAFS spectra for the catalysts and reference compounds (MoSj and NajMoOJ were measured on the BL-lOB instruments of the Photon Factory at the National Laboratory for High Energy Physics by using a synchrotron radiation. The EXAFS spectra were obtained at room temperature without exposing the sample to air by using an in situ EXAFS cell with Kapton windows [12]. Data analysis was earned out assuming a plane wave approximation. 

The IR spectra in Fig.7 indicate the preferential adsorption of NO on the Co sites. It may be conjectured that the Mo sulfide species are physically covered by the Co sulfide species or that Co-Mo mixed sulfide species are formed and the chemical natures of the Co and Mo sulfides are mutually modified. The Mo K-edge EXAFS spectra were measured to examine the formation of mixed sulfide species between Co and Mo sulfides. The Fourier transforms are presented in Fig.8 for MoSx/NaY and CoSx-MoSx/NaY. The structural parameters derived from EXAFS analysis are summarized in Table 1. The structure and dispersion of the Mo sulfides in MoSx/NaY are discussed above. With the Co-Mo binary sulfide catalyst, the Mo-Co bondings are clearly observed at 0.283 nm in addition to the Mo-S and Mo-Mo bondings. The Mo-Co distance is close to that reported by Bouwens et al. [7] for a CoMoS phase supported on activated carbon. Detailed analysis of the EXAFS results for CoSx-MoSx/NaY will be presented elsewhere. It is concluded that the Co-Mo mixed sulfides possessing Co-S-Mo chemical bondings are formed in CoSx-MoSx/NaY. 

We express our thanks to Prof M.Yamada (Tohoku University) for the FTIR measurements and Mr. M.Matsuo (Rigaku Ltd.) for the XPS measurements. We are also grateful to Prof M.Nomura and staff of the Photon Factory, National Laboratory for High Energy Physics, for assistance in measuring EXAFS spectra (F oposals 89138 and 93G163). 

Fig. 10 a UV-Vis DRS spectra of TS-1 (curve 1, full line), immediately after contact with H2O2/H2O solution (curve , dotted line), after time elapse of 24h (curve 3, dashed line) and after subsequent H2O dosage (curve 4, scattered squares), b as for a for the XANES spectra, c as for a for the -weighted, phase imcorrected, FT of the EXAFS spectra. Spectra 2-4 of b and c have been reordered at liquid nitrogen temperatime. Adapted from [49] with permission. Copyright (2004) by ACS... 

For example, treatment of MgO-supported [HIr4(CO)n] in flowing He at 573 K caused essentially complete removal of the CO ligands, as shown by IR and EXAFS spectra, with the Ir4 tetrahedra remaining essentially intact, as shown by EXAFS spectra [12]. IR spectra indicated the formation of carbonate and formate on the basic MgO, which evidently was not an inert platform [19]. When the decarbonylation took place in the presence of H2, the iridium aggregated into larger clusters more readily than when the de-... 

Figure 5. EXAFS spectra of the tetrachloroaurate compound, the Au foil [Au(0)], and the Au in the agar and plant samples. (Reprinted from Ref. [28], 2002, with permission from American Chemical Society.)...

Several quantum-chemical studies have been performed on Hg(CN)2 and related species, applying different approaches with consideration of relativistic effects in order to get MO schemes and energies as a basis for discussion of bonding, valence XPS,105 UPS,106 XANES and EXAFS spectra.41 The latter study also showed Hg(CN)2 to be dissolved in H20 in molecular form (/-(Hg—C) 202, r(C—N) 114 pm), and obviously not to be hydrated, a remarkable finding insofar as solvates of Hg(CN)2 with various donor molecules are well known.2 However, in contrast to Cd(CN)2 (see above), Hg(CN)2 as such does not form clathrates. 

Figure 18. Raw EXAFS spectra for (A) dry Ni(OH)2 electrode (B) a Ni(OH)2 electrode charged once (C) an electrode discharged once (D) an electrode charged twice.

Figure 6.10 shows Fourier transforms of Co K-edge EXAFS spectra of these calcined catalysts and polycrystalline Co oxides. Three peaks are clearly observed in EXAFS spectra of calcined Co(X)/Si02 catalysts at almost the same... 

Coordination Number (N) and Interatomic Distance (R) of Co-O and Co-Co Shells Calculated from Co K-edge EXAFS Spectra of Calcined Catalysts, and Polycrystalline Co304 and a-Co2Si04 (Figure 6.10)... 

Data reduction of EXAFS spectra was performed using WinXAS [14], The normalized spectra were analyzed over the Arrange of 2.5 to 10 A1. A square-weighted degree 7 spline was used to remove the background of the x(k) function. Finally, the data in -space were converted to R-space using a Bessel window to obtain the radial distribution function. 

FIGURE 7.1 (Top) XANES and (bottom) EXAFS spectra (left) as a function of temperature and (right) as a function of time at 270°C in 5% CO/balance inert for the catalyst with an atomic ratio of 100Fe/4.6 Si. 

FIGURE 7.12 Fourier tranform magnitude of kl (k) versus k theoretical EXAFS spectra generated from FEFFIT software by setting coordination numbers to their nominal values, and other EXAFS parameters as described in the experimental section. (Light solid line) Debye-Waller factor of 0.000 and (heavy solid line) Debye-Waller factor of 0.010. Grange of 2.5 to 10 A-1. 

FIGURE 8.5 EXAFS spectra of reference compounds (top) Co metal, (middle) CoO, and (bottom) Co304, including (left) k -x(k) vs. k spectra and (right) corresponding Fourier transform magnitude spectra. 

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