Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

CHAPTER 3
Table 3‐4: Structural parameters obtained from EXAFS data fitting.
Sample Ag‐Ag Shell no. N R (Å) σ 2 (Å ‐2 )
Absorption (a.u.)
Ag foil
10%Ag/SiO2
10%Ag/SiO2 –
CeO2
after 15 min
1.1
1.0
0.9
(a)
(b)
(d)
(e)
1 12 2.86 a
90
0.009
2 6 4.03 0.011
3 24 5.03 0.015
1 7.9 2.86 a
2 6.0 b
0.009
4.01 0.014
3 4.2 5.04 0.007
1 10 2.86 a
2 6.0 b
0.8
25.50 25.53 25.56 25.59
Energy (keV)
0.009
4.01 0.013
3 5.0 5.03 0.006
a Note that the Ag‐Ag distance found is by 0.03 Å too small which is in analogy to examples found
in the literature [68]. b Coordination number was constrained to 6.0.
0 1 2 3 4 5 6 7 8
Figure 3‐8: XANES (left) and Fourier transformed EXAFS (right) spectra of ex‐situ 10%Ag/SiO2 – CeO2 (2:1)
catalyst samples before reaction (a), after 15 min (b), 90 min (c) and 5 h (d) reaction time; (e) silver foil.
FT(χ(k)k 3
)
0.14
0.12
0.10
0.08
0.06
0.04
0.02
(a)
0.00
0 1 2 3 4 5
R (Å)
0.14
0.12
0.10
0.08
0.06
0.04
0.02
(b)
Figure 3‐9: Experimental (solid line) and fitted (dashed line) radial distribution function of fresh 10%Ag/SiO2
catalyst (a), 10%Ag/SiO2 catalyst after 15 min reaction time (b) and silver foil (c). EXAFS data fits were made
up to 5.5 Å for the first three Ag shells.
FT(k 3 χ)(a.u.)
0.15
0.10
0.05
0.00
0.00
0 1 2 3 4 5
R (Å)
0.14
0.12
0.10
0.08
0.06
0.04
0.02
(c)
R (Å)
(c)
(b)
(d)
2.4 2.6 2.8
(e)
(a)
0.00
0 1 2 3 4 5
R (Å)