Selective catalytic reduction of NO with NH3 in presence of oxygen over copper exchanged NaY zeolites

A series of Cu-NaY, prepared by ion-exchange and impregnation, was characte rized by temperature programmed reduction (TPR) and oxidation (TPO) and als o tested for the selective catalytic reduction (SCR) of NO by NH3 in an oxy gen rich atmosphere, and in the NH3 oxidation. From the TPR profiles, the a mount of isolated Cu2+ species, [Cu-O-Cu](2+) dimer species and CuO aggrega tes were evaluated, The TPO of Cu+-NaY issued from the reduction of Cu2+-Na Y 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/O-2 with respect to O-2 alone. The SCR of NO with NH3 in 3% O-2 leads to three peaks in the NO conversion curve, when conducted in the temperature programmed r eaction mode. The first peak is a transient effect due to the impossible re generation of Cu+ to Cu2+. As soon as the reoxydation of Cu+ to Cu2+ become feasible by NO/O-2, the reaction starts (second peak) and would be related to the presence of copper in supercages. The formation of N2O in this temp erature range occurs in the presence of copper oxide aggregates. The final conversion, at high temperature leads to 100% conversion of NO and is due t o a better oxidation of Cu+ by NO/O-2 and O-2 alone. In this latter tempera ture 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.