Promoted Fe/ZSM-5 catalysts prepared by sublimation:: de-NOx activity and durability in H2O-rich streams

Fe/ZSM-5 catalysts with an Fe/Al ratio approximate to 1.0, were prepared by sublimation of FeCl3 into H/ZSM-5. They display high activity and durability for the selective catalytic reduction of NOx to N-2, both in dry and wet gas flows. These catalysts have now been modified by exchanging a second cation into the zeolite. Mere neutralization of zeolite protons by Naf lowers the selectivity for NOx reduction to N-2, but the cations Ce3+ and La3+ act as true catalyst promoters. With isobutane as the reductant in a simulated vehicular emission gas, almost 90% of NOx is reduced to N-2 at 350 degrees C over the La-promoted catalyst. The presence of 10% H2O in the feed does not impair the catalyst performance at high temperature; in the temperature region below 350 degrees C it even increases the N-2 yield. The beneficial effect of La is due to its lowering of the catalyst activity for the undesired combustion of the hydrocarbon. No signs of zeolite destruction are evident after 100 h TOS in a wet gas flow at 350 degrees C. Carbonaceous deposits causing a slight deactivation are easily removed in an O-2/He flow at 500 degrees C; this in situ regeneration fully restores the original activity.