Reduction Rate of NO, NO2 and Equimolal Mixture of NO-NO2 with NH3 over Various Metal Oxide Catalysts Supported on TiO2

For the purpose to establish the reduction mechanism of NOx with NH3, the higher activity catalysts and the operation conditions, the reduction rates of NOx (NO+NO2) of different compositions over the various metal oxide (V2O5, WO3, MoO3, Cr2O3, Mn2O3, Fe2O3, Co3O4, NiO, CuO, ZnO) catalysts supported on TiO2 (average diameter: 1.0mm) were investigated together with the examination of the oxidation of NO to NO2with O2 the decomposition of NO2 to NO, etc.. The experiments were carried out using a flow reactor (I. D.: 12.0mm) at 250, 550°C. Inlet gas concentrations were 500ppmNOx (NO, NO2, NO-NO2 equimolal mixture)-0 or 350-4140ppmNH3 (mainly 667ppmNH3)-5%O2-0 or 10%H2O-N2 for the reduction of NOx, the oxidation of NO and the decomposition of NO2. The apace velocity was mainly 1.1×105hr-1.It was found that the reduction rate of equimolal mixture of NO and NO2 over every metal oxide catalysts employed was markedly high and that the catalysts (V2O5, WO3, MoO3) with higher reduction activity for NO than that for NO2, the catalysts (Mn2O3, Co3O4, Cr2O3, NiO) with higher reduction activity for NO2 than that for NO and catalysts (Fe2O3, CuO, ZnO) with the similar activity for reduction of both NO and NO2 existed. However, the overall reactions were given by the following equations for every metal oxide catalyst.For NO system: NO+NH3+ (1/4) O2→N2+ (3/2) H2OFor NO2 system: NO2+ (4/3) NH3→ (7/6) N2+2H2OFor equirnolal mixture of NO-NO2 system: NO+NO2+2NH3→2N2+3H2OAlso, the correlation between the activity for NO-reduction with NH3 and that for NO-oxidation with O2 was not found from the apparent rate of NO2 gas-formation, but the correlation between the activity for NO2-reduction with NH3 and that for NO2-decomposition to NO was found.