Réduction catalytique sélective de NO par NH3 en présence d'oxygène sur zéolithes NaY échangées au cuivre

Abstract

A series of Cu-NaY, prepared by ion-exchange and impregnation, was characterized by temperature programmed reduction (TPR) and oxidation (TPO) and also tested for the selective catalytic reduction (SCR) of NO by NH3 in an oxygen rich atmosphere, and in the NH3 oxidation. From the TPR profiles, the amount of isolated Cu2+ species, [Cu-O-Cu]2+ dimer species and CuO aggregates were evaluated. The TPO of Cu+-NaY issued from the reduction of Cu2+-NaY by NH3, shows that NO alone cannot perform the reoxidation of Cu+ to Cu2+ below 873 K, but this reaction is enhanced in the presence of NO/O2 with respect to O2 alone. The SCR of NO with NH3 in 3% O2 leads to three peaks in the NO conversion curve, when conducted in the temperature programmed reaction mode. The first peak is a transient effect due to the impossible regeneration of Cu+ to Cu2+. As soon as the reoxydation of Cu+ to Cu2+ become feasible by NO/O2, the reaction starts (second peak) and would be related to the presence of copper in supercages. The formation of N2O in this temperature range occurs in the presence of copper oxide aggregates. The final conversion, at high temperature leads to 100% conversion of NO and is due to a better oxidation of Cu+ by NO/O2 and O2 alone. In this latter temperature range, the formation of N2O comes mainly from the reaction between NO and NH3 in the sodalite cavities but also from the oxidation of NH3.