Study on the durability of Ir catalyst supported on MFI-type metallosilicates for selective reduction of NOx with hydrocarbons

Iridium catalysts supported on MFI-type metallosilicates with activation tr eatment in 10%H2O-N-2 at 700 degrees C showed very high NOX reduction activ ity at 300-500 degrees C under oxygen rich condition. The activated catalyst showed stable NOX reduction activity in lean burn at mosphere with steam gas and rich atmosphere gas treatment and was durable t o SO2-poisoning. This catalyst had stable NOX reduction activity in continuous treatment at 450 degrees C of lean burn gas atmosphere, but showed catalytic deactivatio n in continuous treatment over 500 degrees C of lean burn gas atmosphere. H owever, the activity of deactivated catalyst is easily regenerated by the l ean/stoichiometry alternate gas treatment. Moreover, this catalyst showed s table NOX reduction activity of lean/stoichiometry alternate atmosphere gas treatment for 450 h. The characterization by XRD and XPS revealed that the reason of catalytic d eactivation in continuous treatment of lean burn gas atmosphere was in the form of Ir oxide around the Ir-metal surface. Ir oxide around the Ir-metal surface is easily removed by the hydrocarbon treatment in the stoichiometry gas atmosphere.