NO oxidation over Fe-based catalysts supported on montmorillonite K10, γ-alumina and ZSM-5 with gas-phase HO.

The catalytic gas-phase HO oxidation of NO was achieved over Fe-based catalysts supported on montmorillonite K10, γ-alumina and ZSM-5. ESR tests illustrate that the three catalysts can catalyze decomposition of HO yielding highly reactive hydroxyl radicals, of which Fe/K10 has the fastest rate, followed by Fe/γ-alumina. Fe in Fe/K10 and Fe/γ-alumina show lower density of electron cloud due to a strong interaction between Fe and the support, which benefits the electron transfer from the HO to Fe, thus favoring the production of hydroxyl radicals. Fe species exist on the surface of Fe/K10 mainly in the form of FeO, whereas Fe species of Fe/γ-alumina and Fe/ZSM-5 exist mainly in the form of FeO, and it is found that FeO is more active than FeO in catalytic gas-phase HO oxidation of NO. Interestingly, Fe/ZSM-5 has the lowest efficiency in generating hydroxyl radicals, its NO removal efficiency is 90%, which is much higher than 47.5% for Fe/γ-alumina and 62.3% for Fe/K10. In-situ IR results suggested that Fe/ZSM-5 are dual functional in oxidation of NO, that is, whether both Fe ion sites and Brønsted acid sites collectively provide the catalytic functionality. In the meantime, a possible reaction mechanism on catalytic gas-phase HO oxidation of NO over Brønsted acid sites is proposed.