27 research outputs found
Réduction catalytique sélective de NO par NH
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.