Highly active and stable bimetallic Ir/Fe-USY catalysts for direct and NO-assisted N2O decomposition

The current research investigated N₂O decompositions over the catalysts Ir/Fe-USY, Fe-USY and Ir-USY under various conditions, and found that a trace amount of iridium (0.1 wt%) incorporated into Fe-USY significantly enhanced N₂O decomposition activity. The decomposition of N₂O over this catalyst (Ir/Fe-USY-0.1%) was also partly assisted by NO present in the gas mixture, in contrast to the negative effect of NO over noble metal catalysts. Moreover, Ir/Fe-USY-0.1% can decompose more than 90% at 400 °C (i.e. the normal exhaust temperature) under simulated conditions of a typical nitric acid plant, e.g. 5000 ppm N₂O, 5% O₂, 700 ppm NO and 2% H₂O in balance He, and such an activity can be kept for over 110 h under these strict conditions. The excellent properties of bimetallic Ir/Fe-USY-0.1% catalyst are presumably related to the good dispersion of Fe and Ir on the zeolite framework, the formation of framework Al–O–Fe species and the electronic synergy between the Ir and Fe sites. The reaction mechanism for N₂O decomposition has been further discussed on the temperature-programmed desorption profiles of O₂, N₂ and NO₂.