Besides that, the Cr-doped TiO 2 catalysts chemically prepared by impregnation or
sol–gel method were found to have a mixture of the aggregated Cr-oxides in
tetrahedral coordination similar to CrO 3 and octahedral coordination similar to
Cr 2 O 3 .
Fig. 3.12 Relationship between the coordination numbers and photocatalytic reactivity of titanium
oxides. (Reprinted with permission from Ref. [78]. Copyright 1997, American Chemical Society)
Table 3.1 Comparisons of yields of N 2 and N 2 O and their selectivities in the direct photocatalytic
decomposition of NO at 275 K on various types of the Ti-oxide/zeolite catalysts and the powered
bulk TiO 2 catalyst
Catalysts
Ti content (wt% of as TiO 2 )
Yields (μmol/g-catal
h)
Selectivity
(%)
N 2
N 2 O
total
N 2
N 2 O
ex-Ti-oxide/Y-zeolite
1.1
14
1
15
91
9
imp-Ti-oxide/Y-zeolite
1.0
7
10
17
41
59
imp-Ti-oxide/Y-zeolite
10
5
22
27
19
81
Powered TiO 2
100
2
6
8
25
75
3.5 The Development of Mesoporous Ti–SiO 2 Materials in Photocatalysis
67