Vanadium XANES

Vanadium K-edge XANES measured in transmission mode at 15 K showed that the attached V complex (2) maintained its square pyramidal conformation with a V=0 bond (Figure 2.2a). Curve-fitting analysis of V K-edge EXAFS Fourier transforms (Figure 2.2b) provided local structure information on the supported V complex (2) with an unsaturated conformation, which differs from that of the V-monomer precursor (1). The EXAFS curve-fitting was performed in the R-space with two shells short V=0 and long V—O bonds. A V=0 bond was observed at 0.157 0.001 nm,... 

The oxidation states of antimony, vanadium, and molybdenum in a "MoVSbNbO" propane-to-acrylic acid catalyst were probed by XANES... 

Fjo. 8. Oxidation state versus energy positions of various absorption features in the V K edge XANES spectra of various vanadium oxides. From Wong era/. (3/2). 

Comparison of the XANES spectra of the vanadium layer on Ti02 prepared by two different routes (by alkoxide precipitation and via VOCl3) shows close analogy. This indicates that the simple precipitation technique without chemical reaction between the vanadium reagent and the surface leads to a disordered monolayer on Ti02. Similar data have also been reported for the V205/y-Al203 system (147). 

Some examples of using XANES to obtain information about the immediate local environment of the atom being probed are Woolery et al s study of the vanadium species found in used FCC catalysts. Bouwens et al have used the variation of the intensity of pre-edge XANES features in Co containing catalysts to identify the symmetry of ligands bound to Co in Co-Mo-S hydrodesulfurization (HDS) catalysts. 

Based on the studies of the XANES (X-ray absorption near edge structure) spectra of LiVMoOe and the standard samples (such as V2O5, VO2, M0O3, M0O2, etc) at the V and Mo K-edges, we can determine the valence of the vanadium ion is about 4.5 while that of molybdenum ion is 6. 

Fig, 3, Vanadium K-edge and XANES of the VFe protein of A. chroococcum and a VFe3S4 cubane cluster, (a) Dithionite-reduced VFe protein (b) [VFe3S4Cl3(DMF)3). ... 

Table 3.6 XANES data on selected vanadium compounds. Energy positions are given in eV relative to vanadium metal foil (pre-edge = 5465.0 eV).

Fig. 16. Comparison of the K XANES of 0.1 wt.-% vanadium doped silica glass and of Na CrO j documents tetrahedral coordination of vanadium in the glass. This shows the application of XANES for local structure determination in disordered materials. The analogy of the overall shape of the XANES spectra is obtained by dilation of the energy scale with a factor 1/d = 0.318 (d = 1.77 A) of the energy scale of the glass spectrum...

In Fig. 18 we. report the vanadium K-edge XANES spectra of a spontaneously dehydrated sol-gel sample 1.6 H O. This sample is formed of oriented sheets separated by about 10 A of water molecules. Each sheet consists of square plane bipyramids with the base on the xy plane and a short double bond of 1.58 A on one... 

Delaney JS, Sutton SR, NewviUe M, Jones JH, Hanson B, Dym MD, Schreiber H (2000) Synchrotron micro-XANES measrrrements of vanadium oxidation state in glasses as a function of oxygen fugacity ... 

Silk JE, Hansen LD. Eatough DJ, Hill MW, Mangelson NF, Lytle FW, Greegor RB (1989) Chemical characterization of vanadium, nickel, and arsenic in oil fly-ash samples using EXAFS and XANES spectroscopy. Physica (Amsterdam) 158 247-248... 

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