For the purpose to establish the reduction mechanism of NO
x with NH
3, the higher activity catalysts and the operation conditions, the reduction rates of NO
x (NO+NO
2) of different compositions over the various metal oxide (V
2O
5, WO
3, MoO
3, Cr
2O
3, Mn
2O
3, Fe
2O
3, Co
3O
4, NiO, CuO, ZnO) catalysts supported on TiO
2 (average diameter: 1.0mm) were investigated together with the examination of the oxidation of NO to NO
2with O
2 the decomposition of NO
2 to NO, etc.. The experiments were carried out using a flow reactor (I. D.: 12.0mm) at 250, 550°C. Inlet gas concentrations were 500ppmNO
x (NO, NO
2, NO-NO
2 equimolal mixture)-0 or 350-4140ppmNH
3 (mainly 667ppmNH
3)-5%O
2-0 or 10%H
2O-N
2 for the reduction of NO
x, the oxidation of NO and the decomposition of NO
2. The apace velocity was mainly 1.1×10
5hr
-1.
It was found that the reduction rate of equimolal mixture of NO and NO
2 over every metal oxide catalysts employed was markedly high and that the catalysts (V
2O
5, WO
3, MoO
3) with higher reduction activity for NO than that for NO
2, the catalysts (Mn
2O
3, Co
3O
4, Cr
2O
3, NiO) with higher reduction activity for NO
2 than that for NO and catalysts (Fe
2O
3, CuO, ZnO) with the similar activity for reduction of both NO and NO
2 existed. However, the overall reactions were given by the following equations for every metal oxide catalyst.
For NO system: NO+NH
3+ (1/4) O
2→N
2+ (3/2) H
2O
For NO
2 system: NO
2+ (4/3) NH
3→ (7/6) N
2+2H
2O
For equirnolal mixture of NO-NO
2 system: NO+NO
2+2NH
3→2N
2+3H
2O
Also, the correlation between the activity for NO-reduction with NH
3 and that for NO-oxidation with O
2 was not found from the apparent rate of NO
2 gas-formation, but the correlation between the activity for NO
2-reduction with NH
3 and that for NO
2-decomposition to NO was found.
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