Iron-substituted TNU-9, TNU-10, and IM-5 zeolites and their steam-activated analogs as catalysts for direct N₂O decomposition

Isomorphously substituted Fe-TNU-9, Fe-TNU-10, and Fe-IM-5 zeolites containing both Fe and Al in framework positions have been hydrothermally synthesized and tested as catalysts for direct N₂O decomposition, together with their steam-activated analogs. When compared with the catalytic results obtained from the corresponding forms of Fe-ZSM-5 with a similar Fe content, the specific activity per mole of iron is higher in the order Fe-TNU-10 < Fe-IM-5 < Fe-TNU-9 < Fe-ZSM-5. While all these catalysts have a promoting effect of NO on N₂O decomposition, they exhibit different extents of increase in activity by NO addition, suggesting differences in the type of their extra-framework iron species. From the overall characterization results of our study, we can conclude that the thermal stability of Fe in framework positions differs notably according to the structure type of zeolites, which may have an intrinsic effect upon the nature and distribution of extra-framework iron species, and thus upon their N₂O decomposition activity.