Sulfur K-edge

X-ray absorption near edge structure (XANES) spectroscopy is a non-destructive and sensitive probe of the coordination number and geometry as well as of the effective charge of a chosen atom within a molecule and therefore also of the formal oxidation number. Recently, there have been a number of XANES studies at the sulfur K-edge demonstrating the sensitivity of... 

Sulfur K Edge X-ray Absorption and X-ray Photoelectron Spectroscopic Approaches... 

A Sulfur K Edge X-ray Absorption Near Edge Structure (XANES) Spectroscopy method has been developed for the direct determination and quantification of the forms of organically bound sulfur in nonvolatile petroleum and coal samples. XANES spectra were taken of a number of model compounds, mixtures of model compounds, heavy petroleum and coal samples. Analysis of the third derivatives of these spectra allowed approximate quantification of the sulfidic and thiophenic components of the model mixtures and of heavy petroleum and coal samples. These results are compared with those obtained by X-ray Photoelectron Spectroscopy (XPS). 

XANES of Model Compounds. Table I lists the first inflection points of the sulfur K edge spectra for a series of model compounds whose structures are believed to be representative of the types of organically bound sulfur found in heavy petroleum and coals. 

XANES of Petroleum Residua. On the left side of Figure 1 the sulfur K edge spectra for three different petroleum residua and the asphaltene samples prepared from them are shown. While the absorption spectra all appear to be similar, differences are revealed by examining the third derivatives of the spectra, which are shown on the right side of the figure. All the residua samples appear to contain sulfur bound in sulfidic and thiophenic forms, the amount of sulfidic sulfur increasing from sample 1 to sample 3. The asphaltene samples prepared from residua 2 and 3 also appear to contain both forms. Assuming that the composition of the sulfur... 

Table I. Sulfur K Edge First Inflection Energies (a)...

Sulfur K-edge NEXAFS also detected significant differences between oxidation states in hydrophobic and hydrophilic organic matter (Hundal et al., 2000). Oxidized organic sulfur forms were dominant in the hydrophilic fraction, whereas reduced sulfur forms were dominant in the hydrophobic fraction. 

Solomon, D., Lehmann, J., and Martinez, C. E. (2003). Sulfur K-edge XANES spectroscopy as a tool for understanding sulfur dynamics in soil organic matter. Soil Sci. Soc. Am. J. 67, 1721-1731. 

Szilagyi, R. K., and Schwab, D. E. (2005). Sulfur K-edge X-ray absorption spectroscopy as an experimental probe for S-nitroso proteins. Biochem. Biophys. Res. Comm. 330, 60-63. 

FIGURE 1.25 Sulfur K-edge spectra for blue copper site in plastocyanin and the Cu(II) model complex tet b.49 Inset shows the MO diagram for a transition to the half-occupied HOMO. 

Primary basaltic glass inclusions trapped in olivines and representative of magmas from active volcanoes have been studied by X-ray spectromicroscopy, in order to understand the excess degassing of sulfur dioxide (S02) [31]. The p-XANES experiments at the sulfur K edge were carried out on the x-ray microspectroscopy beamline ID21 (ESRF, France) with a spot size range from 0.5x0.5 pm2. 

The utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in nonvolatile hydrocarbons has been investigated. X-ray Absorption Near Edge Structure (XANES) spectra were obtained for a selected group of model compounds, for several petroleum asphaltene samples and for Rasa coal. For the model compounds the sulfur XANES was found to vary widely from compound to compound, and to provide a fingerprint for the form of sulfur involved. The use of third derivatives of the spectra enabled discrimination of mixtures of sulfide and thiophenic model compounds, and allowed approximate quantification of the amount of each component in the mixtures, in the asphaltene samples and the coal. These results represent the first demonstration that nonvolatile sulfide and thiophenic sulfur forms can be distinguished and approximately quantified by direct measurement. 

Figure 1. Sulfur K-edge XANES spectra and formulae of selected model compounds illustrating the diversity of sulfur XANES spectra. All data have been normalized to the height of the edge jump. Because of the intensity of the spectrum of K2SO4 the vertical scale has been expanded by a factor of two.

Figure 7. Ground-state wave function of plastocyanin. A HOMO wave function contour for plastocyanin (28). B HOMO wave function contour for the thiolate copper complex tet b (34/ C Copper L-edge (38) and sulfur K-edge (34) spectra as probes of metal-ligand covalency. D Absorption, single-crystal polarized absorption, and low-temperature MCD spectra of plastocyanin. The absorption spectrum has been Gaussian resolved into its component bands as in reference 33.

Supported ruthenium carbido-cluster catalysts for the catalytic removal of nitrogen monoxide and sulfur dioxide the preparation process monitored by sulfur K-edge X-ray absorption near-edge structure... 

The preparation process of ruthenium carbido-cluster catalysts for the reduction of sulfur dioxide was traced by means of sulfur K-edge X-ray absorption near-edge structure (XANES). During the activation process, a pair of peaks at 2472.5 - 2472.8 and 2482.7 -2482.8 eV appeared. The pair was ascribed to the RuS phase. Once the catalysts were activated at 503 - 573 K, another pair of peaks at 2474.2 and 2479.2 eV appeared. The pair was assigned to the it and a transition peaks, respectively, of adsorbed SO molecules on the catalyst surface. 

In this manuscript, the third factor was studied by sulfur K-edge X-ray absorption near-edge structure (XANES). Infrared absorption spectroscopy is often used to monitor the adsorbed/intermediate species on the surface. However, by infrared absorption, the atoms dissociated from reactant molecules that are buried into the catalysts are often inaccessible, e.g. sulfur atom of SO dissociated and reacted to form the RuS phase. The major objective of this paper is to monitor both adsorbed and buried sulfur atoms by S K-edge XANES in the preparation process of supported ruthenium catalysts. 

The Peak energy positions of sulfur K-edge XANES for [Ru Cj/TiOj and conv-Ru/TiO catalysts and reference inorganic/organometallic compounds... 

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