The mechanical mixing of Mn2O3 or CeO2 to Ce-ZSM-5 considerably enhanc
ed the rate of the reduction of NO by propene in the low to medium tem
perature region, although Mn2O3 or CeO2 itself was much less active fo
r this reaction. In contrast, Mn2O3 was highly active and CeO2 was mod
erately active for the oxidation of NO to NO2. On the basis of the com
parison of the rates of the C3H6 + O2, NO + C3H6 + O2 and NO2 + C3H6 O2 reactions over these catalysts, a bifunctional mechanism is propos
ed, in which Mn2O3 and CeO2 accelerate the oxidation of NO and the sub
sequent reaction steps between NO2 and propene proceed on Ce-ZSM-5.