Chemistry Reference
In-Depth Information
environment found in the pyrochlore, the HTB phase displays various environments:
hydroxylated, fluorinated and mixed OH/F. This can be rationalized by the large range of
interatomic distances lying from 1.78 to 1.85
˚
. The occurrence of distinct hydroxylated
and fluorinated sites is assumed to induce an electronic heterogeneity around the Al
3
þ
ions. It should be noted that for both phases three components have been also detected for
F1s BEs i.e. 686.8, 685.7 and 684.7 eV. Interestingly, the XPS data reflects the acidity
displayed by both solids. Adsorption of probe molecules has indeed confirmed the
homogeneous and heterogeneous acidity for the pyrochlore
42
and HTB
59
phases,
respectively.
1
2
3
Pyrochlore
AlF
1.7
(OH)
1.3
4
1
2
β
-AlF
2.6
(OH)
0.4
3
−20
−40
10
0
−10
−30
δ
iso
(ppm)
Figure 2.10
27
Al MAS NMR spectra of the pyrochlore AlF
1.7
(OH)
1.3
and the HTB-type
b
-AlF
2.6
(OH)
0.4
compounds
Table 2.7 Line label, isotropic chemical shift
d
iso
(ppm), quadrupolar product
Q
(kHz),
relative line intensity (%) deduced from the reconstruction of the
27
Al MAS NMR spectrum,
with corresponding assignments. For a sake of clarity, the very weak
27
Al NMR signals located
at
d
iso >10 ppm ascribed to the partial decomposition of the pyrochlore has not been
mentioned
Assignment of the
27
Al NMR lines
Line
iso
(
-
0.5)
Q
(
-
5)
Relative Intensity (
-
0.5)
Pyrochlore AlF
1.7
(OH)
1.3
1
-12.5
345
47.3
AlF
6
, AlF
5
(OH) and AlF
4
(OH)
2
2
-8.7
540
33.4
AlF
3
(OH)
3
3
-4.2
625
15.5
AlF
2
(OH)
4
4
1.8
505
3.9
AlF(OH)
5
-AlF
2.6
(OH)
0.4
1
-15.5
280
82
AlF
6
and AlF
5
(OH)
2
-11.7
610
16
AlF
4
(OH)
2
3
-9.5
990
2
AlF
3
(OH)
3
