THE ROLE OF NO2 IN THE REDUCTION OF NO BY HYDROCARBON OVER CU-ZRO2 AND CU-ZSM-5 CATALYSTS

The reduction of NOx with propene or propane in the presence of 1 or 4% O-2 was studied at low conversions over a 7.4 wt% Cu-ZrO2 and a 3.2 wt% Cu-ZSM-5 catalyst. The rates of N-2 production were compared in experiments using only NO or a mixture of NO and NO2 in the feed. They were also compared with the rates of NO2 reduction to NO under the same conditions, and of NO oxidation to NO2 in the absence of hydrocarbon. It was found that the reduction of NO2 to NO was very fast, consistent with literature data. The data were best explained by a reaction scheme in which the hydrocarbon was activated primarily by reaction with adsorbed NO2 to form an adsorbed oxidized N-containing hydrocarbon intermediate, the reaction of which with NO was the principal route to produce N-2 under lean NOx conditions.