Page 103 - Principles of Catalyst Development
P. 103
90 CHAPTER 5
5.2.6. Necessary Catalyst Properties
This step is merely a redefinition of the surface mechanism in terms
of properties helpful in the search for appropriate materials. The catalyst
must have
1. Oxygen adsorption sites, leading to dissociation and immobile oxy-
gen species.
2. Mild dehydrogenation sites that give CH 3 from CH 4 and remove H
from the intermediate.
3. Adjacent sites in order to facilitate the final dehydrogenation step.
5.2.7. Search for Appropriate Materials
The requirement for mild dehydrogenation and low oxidation elimi-
nates most metals, focusing the search upon oxides. Figure 5.4 shows a
typical pattern of activity for dehydrogenation. (45) High activity is centered
around ions with d and d configurations. Mild dehydrogenation is found
4
6
in oxides containing ions such as Cu 2 +, Ni 2 +, Fe H , Mn2t, y3+, y5+, and Ti4+.
l r ---,--
I
I
>- l
I-
> I
u I
l-
W ~
<I:
>
i=
<I:
....J
W
a:
Co 0 CuO ZnO
3 4
Figure 5.4. Dehydrogenation patterns in oxides.