EXAFS as a tool for catalyst characterization: a review of the ... - INT
EXAFS as a tool for catalyst characterization: a review of the ... - INT EXAFS as a tool for catalyst characterization: a review of the ... - INT
necessary to perform the fit with Pd and Co atoms (Table 2). This results in a mean palladium concentration of only 7.7% around a Co atom, which is much lower than that expected from chemical analysis, indicating that Co atoms tend to be preferentially surrounded by Co atoms. Figure 5: Amplitude of the Radial Distribution Function at the Co K-edge for cobalt foil (solid line) and Co/G (dotted line) and Pd 16 Co 84 /G (dashed line). Table 2: EXAFS parameters at the Co K-edge Co - Co pair Co - Pd pair Sample n 1 R 1 (Å) σ 2 (Å 2 ) n 2 R 2 (Å) σ 2 (Å 2 ) Q (%) n 1 +n 2 Co foil 12.0 2.51 - - - - - - Co/G 11.5 2.50 0.0020 - - - 3 11.5 Pd 16 Co 84 /G 8.0 2.50 0.0060 3.7 2.61 0.0080 9 11.7
Therefore, the EXAFS analysis demonstrated that the alloy phase was formed during reduction, as already shown by magnetic and X-ray diffraction measurements (Noronha, 1994). The bimetallic particles consist of both palladium and cobalt rich phases. CONCLUSIONS A review of the EXAFS data analysis methods was presented. A detailed description of the EXAFS signal extraction and the Fourier transform of the data were discussed. The procedure for determining interatomic distances, coordination numbers and disorder effects from EXAFS data was described. These parameters were calculated in order to obtain both further evidence of Pd-Co interaction and the mean composition of bimetallic particles. NOMENCLATURE Aj(κ ) the backscattering amplitude from each of the N j neighboring atoms E photoelectron energy E 0 energy of the absorption edge Planck`s constant divided by 2π h.ν energy of the X-ray photon I 0 photon intensities before the absorber I photon intensities after the absorber m mass of the electron N j number of atoms in the j th shell N ind number of independent points N par number of parameters p i fitting parameters
- Page 1 and 2: EXAFS as a tool for catalyst charac
- Page 3 and 4: Figure 1: Regions of the X-ray abso
- Page 5 and 6: The normalized EXAFS spectrum assoc
- Page 7 and 8: (11) I 0 - modified BESSEL function
- Page 9 and 10: Thus, the resulting curves are fitt
- Page 11: Figure 4: Amplitude of the Radial D
- Page 15 and 16: Bart, J.C.J. and Vlaic, G., Adv.Cat
necessary to per<strong>for</strong>m <strong>the</strong> fit with Pd and Co atoms (Table 2). This<br />
results in a mean palladium concentration <strong>of</strong> only 7.7% around a Co<br />
atom, which is much lower than that expected from chemical<br />
analysis, indicating that Co atoms tend to be preferentially<br />
surrounded by Co atoms.<br />
Figure 5: Amplitude <strong>of</strong> <strong>the</strong> Radial Distribution Function at <strong>the</strong> Co K-edge <strong>for</strong> cobalt<br />
foil (solid line) and Co/G (dotted line) and Pd 16 Co 84 /G (d<strong>as</strong>hed line).<br />
Table 2: <strong>EXAFS</strong> parameters at <strong>the</strong> Co K-edge<br />
Co - Co pair<br />
Co - Pd pair<br />
Sample n 1 R 1 (Å) σ 2 (Å 2 ) n 2 R 2 (Å) σ 2 (Å 2 ) Q<br />
(%)<br />
n 1 +n 2<br />
Co foil 12.0 2.51 - - - - - -<br />
Co/G 11.5 2.50 0.0020 - - - 3 11.5<br />
Pd 16 Co 84 /G 8.0 2.50 0.0060 3.7 2.61 0.0080 9 11.7
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