Page 104 - Principles of Catalyst Development
P. 104
DESIGN OF CATALYSTS 91
Oxygen insertion activity in oxides is essentially mild oxidation. Clues
for potential materials are found from three sources. The first is a pattern
of behavior for CO oxidation, giving(l5J)
'd'
Strong OXI atlOn: C 2+ N· 2 + C 2+ Pd 4 + A 1+ Cd l + M 2+
,n
u,
, g,
,
1 ,
0
Moderate oxidation: Rh +, InH, Sn H , Pb +
1
4
4 2
6
Mild oxidation: Sc H , Ti +, y3+, Cr H , Fe +, Zn2+, Zr1+, Nb1+, Mo +
Second, oxygen mobility correlates well with oxidation. IIS2 ) Available
measurements give the sequence
CO,04> Mn01 > NiO > CuO > Fe2 0J > Cr 20, > Y20S > MoO,
Third, activity for strong oxidation is found in oxides that reduce easily,
suggesting that reduction followed by oxidation may be a mechanism. 14S !
Oxides that are hard to reduce include
Aluminates: CoAI 2 0 4 , NiAI 20 4
Titanates: ZnTi0 4
5.2.8. Proposed Catalyst
By excluding strong oxidation ions from the mild dehydrogenation list,
we arrive at the following listing in order of decreasing activity:
Mild dehydrogenation Oxygen insertion
Fe H SC 3 +yH
y3+ Ti 4 +
V'"~ yH
Ti 4 + Fe 2 +
Zn2+
Zr 3 +
Nb3+
Mo6+
Candidates that are consistent with all these properties are
Single oxides: TiO l , Y203
Mixed oxides: TiO l + MoO], ZnO + Y203
Complex oxides: FeJ04, Fe molybdate, Zn TiO]
Dispersion will not be necessary, since high areas only facilitate complete
oxidation. Therefore, simple methods of preparation will be sufficient. These
materials are suggestions only. No priorities can be assigned and each must
be tested. Only then may the next task of optimization and modification
proceed.