Spectrokinetic study of the mechanism of NO x reduction with propylene over ZrO2 in excess oxygen

It has been demonstrated by quantitative spectrokinetic measurements that, on the surface of zirconia stabilized as a tetragonal phase, the rate-limiting step of the selective catalytic reduction of nitrogen oxides (SCR of NOx) with propylene is the interaction of surface nitrates with C3H6 yielding organic nitro compounds. It is hypothesized that propylene reacts not with the nitrates themselves but with the activated complex NO2ads whose structure is intermediate between the structures of the monodentate NO3− and NO2 species. Deep C3H6 oxidation exerts an adverse effect on the rate of the SCR of NOx with propylene, and the interaction between O2 and NO, which yields NO2 and NO3− stimulates further nitrogen reduction to N2. The effect of the reaction between oxygen and O2N−CnHm on the NOx reduction rate is variable and is determined by the C3H6/NOx ratio. A generalized scheme of the SCR of NOx with propylene on the surface of ZrO2 partially stabilized as a tetragonal phase has been developed by comparing experimental data of this study and data available from the literature.