EXAFS particle sizes

XRD diagram corresponding to the corrected EXAFS particle sizes (solid line in Fig. 12) is in good agreement with the experimentally obtained XRD results. 

XANES/EXAFS) Particle size Complex dieoretical analysis... 

B.J.H. methods) (iii) the average diameter (T.E.M.) and/or the dispersion (chemisorption of probe molecule) of the metallic particle. EXAFS will also provide average coordination numbers, which decrease sharply as the particle size decreases. 

Thus, it becomes possible to obtain supported Rh catalysts containing very small Rh particles. In samples of Rh(T0A)/y-Al203 (1% (w/w)) the Rh particle sizes are around 1.1 nm, as indicated by HRTEM analysis (Figure 8). EXAFS (Extended X-ray Absorption Fine Spectroscopy) studies performed on the same samples give 0.7-1.0 nm as a better estimate of the value [24]. It is noteworthy that the... 

The EXAFS study on Ru-Cu/Si02 of Sinfelt et al. [39] is one of the few examples where conclusions can be drawn on a qualitative base without the need to construct computer fits to the data. The following example illustrates EXAFS as a quantitative tool in a study of particle sizes. 

The interesting information is the correlation between first shell coordination numbers from EXAFS and H/M values from chemisorption, shown in Fig. 6.18. The correlation is as expected high dispersions correspond to low coordination numbers. Of course, what we really need is a relationship between particle size and H/M values. The right hand panel of Fig. 6.18 translates the experimentally determined H/M values of the catalysts into the diameter of particles with a half-spherical shape. Similar calibrations can be made for spherical particles or for particles of any other... 

CO and particle size, 39 159 CO on zeolite-encaged metal, 39 158 EXAFS functions, 39 155-157 Pd particle location and size, 39 155-158... 

The catalysts used in low temperature fuel cells are usually based on small Pt particles dispersed on a carbon support with typical particle sizes in the range 1 — 10 nm in diameter. The XAS provides a measure of the average electronic state and local coordination of the absorbing atom, for example, Pt, on a per-atom basis, as described above. Thus, the XAS, for both the XANES and EXAFS regions, of such Pt/C catalysts reflects the size of the particles. 

The effects of particle size on the EXAFS region of the XAS spectra are reflected in the coordination numbers obtained in the fits to the EXAFS data. Figure 15 shows the EXAFS or xi ) data and corresponding Fourier transforms for a Pt foil, a Pt02... 

Fig. 12. Cu(lll) diffraction line from a reduced Cu/Si02 catalyst acquired by using the combined XRD/EXAFS setup. The dashed line shows the calculated broadening of the Cu(111) peak corresponding to particles with the mean size determined by use of the standard EXAFS analysis. The full line shows the results when the new procedure (34) was used to estimate the copper particle size [adapted from Clausen et at. (34)].

In this study we present the first in-situ formation of a ternary transition metal oxide within the pores of MCM-48 silica. XRD measurements showed the preservation of the host structure as well as the formation of 5-6 nm small particles. In addition, the analysis of nitrogen physisorption data revealed the existence of mesopores with smaller pore diameters and surface areas in comparison to the pristine phase, which can be attributed to the introduction of the Co/Fe/O phase into the pores. First qualitative XANES and EXAFS analyses support the formation of CoFe204 nanoparticles. TEM investigations on particle size and structure are in progress. To learn more about the properties of the oxide nanoparticles Mossbauer and magnetic measurements have to be carried out, which are planned for the future. 

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