XANES analysis

Coordination number and geometry from XANES analysis... 

Figure 29. Pt d band vacancy per atom obtained from XANES analysis at the Pt L3 and Lz edges for PtRu/C (filled circles) and PtMo/C (filled squares) as a function of the applied potential in 1 mol dm HCIO4 + 0.3 mol dm methanol. (Reproduced with permission from ref 103. Copyright 2002 Elsevier Sequoia S.A., Lausanne.)...

SXRF imaging and XANES analysis were made at the PNC/XOR beamline at the Advanced Photon Source, Argonne National Laboratory (Heald. et al 2007) using photon energies of 17.0 and 12.5 keV for SXRF imaging and 11.8 to 12.1 keV for XANES analysis. XANES analysis across the Au L3 edge used steps of 5 eV (from 11.82 - 11.89 keV), 0.5 eV (from 11.89-11.97 keV) and 0.07 k (from 11.97-12.1 keV) with a one second dwell per step. 

In sample 1, it is clear that the predominant form of sulfur in the residuum is thiophenic, while the sulfide forms seem to predominate in residua 2 and 3. In asphaltene samples 1 and 3, the thiophenic sulfur content increases relative to the respective residua, indicating that the molecules containing sulfide sulfur may be more soluble in heptane than those containing thiophenes. For sample 2, there appears to be no such discrimination within the 10% accuracy limits currently established for the XANES analysis. 

In agreement with the XANES analysis, residuum sample 1 contains the highest level of thiophenic-like forms and residuum sample 3 the least. 

Table 6.4 Composition and notation of catalysts submitted to XPS and EXAFS/XANES analysis(Reproduced from Reference [30].)...

Supported nanoparticles (1-1.5 nm) based on Ru4Pt2 entities have been obtained by using a Ru4Pt2(CO)i8 precursor on carbon black and fullerene soot [63]. XANES analysis showed differences between the interaction of nanoparticles with both carbon black and fullerene supports. In particular, a change in the electronic properties of the nanoparticles on fullerene is proposed this change was related to a strong interaction between the nanoparticle and a surface-atom, probably via the formation of a Ru-carbide phase. 

XANES analysis also confirmed that the outer surfaces of the ORR active alloy crystallites are almost entirely Pt the alloying element was relegated to the subsurface layers. This study likewise verifies insignificant dissolution of the alloying element, even at potentials as high as 0.9 V, after the initial formation of the Pt skin as reported by others under PAFC s operating conditions [58,59]. 

Figure 26. EXAFS and XANES analysis scheme. Top left Raw data with background removed.

Figure 31. XANES and EXAFS analysis of the surface structure in 1.9-nm nanoparticles of T102. Top XANES analysis focussing on the pre-edge region. Intensification of the features in this region are consistent with distorted or reduced Ti coordination. Bottom EXAFS analysis shows reduced peak area and coordination in the same samples with XANES intensification. Both analyses point to 5-coordinated Ti on particle surfaces. Capping the particles with ascorbic acid removes the distorted sites. After Chen et al. (1999).

Waychunas GA (1987) Synchrotron radiation XANES spectroscopoy of Ti in minerals Effects of Ti bonding distances, Ti valence, and site geometry on absorption edge stracture. Am Mineral 72 89-101 Waychunas GA, Fuller CC, Davis JA, Rehr JJ (2001) Surface complexation and precipitate geometry for aqueous Zn(II) sorption on ferrihydrite II. XANES analysis. Geochim Cosmochim Acta (in press)... 

The XANES is interpreted as electronic transitions to empty valence states of the absorbing atom. XANES analysis is conducted by comparison of the absorption spectra of the paste of the adsorbent with ions of interest adsorbed on it on the one hand, and of a series of compounds involving the ions of interest on the other. This series can include ... 

In another report. Hansel et al. (2002) studied Fe plaque associated with the rhizosphere of Typha latifolia and Phalaris arundinacea from a mine waste-contaminated site that was high in As. For both plants, the Fe and As concentrations associated with roots were approximately 10-fold concentrated on roots relative to their abundances in the bulk soil. XRF revealed that Fe plaque consisted primarily of ferrihydrite but also had appreciable levels of goethite and siderite T. latifolia also had a significant amount of lepidocrocite. Their analysis suggested that As was sequestered fairly homogeneously within the Fe plaque. A XANES analysis indicated that approximately 80% of the As was As(V) and 20% As(III). Blute et al. (2004) reported similar ratios for As(V) and As(III)... 

X-ray absorption is a powerful technique to obtain local electronic and structural properties and has been widely used to characterize catalysts (Yokoyama 1995). This technique involves the determination of the electronic state through X-ray absorption near edge structure (XANES) analysis and of the local structure through the extended X-ray absorption fine structure (EXAFS). The data can be collected not only in a static but also in dynamic state (in-situ conditions) allowing one to study the catalyst during pretreatment and catalytic reaction. 

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