Catalytic reduction of NO with ammonia over Cu(II) NaY

Abstract

The mechanism of the catalytic reduction of NO with NH 3 over Cu(II) ion-exchanged Y-type zeolites [Cu(II) NaY] was examined by kinetic and isotopic tracer studies as well as relevant studies on the transient reaction of reduced catalysts. The rate of the NONH 3 reaction showed dependence on the partial pressures of both No and NH 3, in accordance with the Langmuir-Hinshelwood type of rate equation. The isotopic tracer studies using 15N-labeled ammonia and NO indicated that N 2 was mainly formed by bi-molecular reaction between NO and ammonia, while the nitrogen atom of nitrous oxide came soley from NO. These results support the reaction mechanism previously proposed. It has been shown that the “bell-shaped” catalytic activity-temperature relation of Cu(II) NaY is associated with the redox change of copper ions. The reoxidation step of Cu(I) ions to Cu(II) was studied in detail by allowing the reduced catalyst to react with gaseous mixtures of NO and NH 3 under various conditions. The results showed that Cu(I) ions were oxidized to Cu(II) by coupling with the stoichiometric disproportionation reaction of NO. The reaction was strongly promoted by the coexistence of NH 3. Based on these results, the mechanism and the rate-determining step of the catalytic NONH 3 reaction were discussed.