Selective catalytic oxidation (SCO) of ammonia to nitrogen over Fe-exchanged zeolites prepared by sublimation of FeCl₃

Fe-exchanged zeolites were prepared by subliming FeCl₃ and studied as catalysts for selective catalytic oxidation (SCO) of ammonia to nitrogen in the presence of oxygen. Fe-ZSM-5 prepared by sublimation of FeCl₃ at 700°C showed excellent SCO performances at a very high space velocity (GHSV=2.3×10⁵ h^-1). Over 99% NH ₃ conversion and nearly 100% N₂ selectivity were obtained at 400°C. Among Fe-ZSM-5 catalysts prepared by subliming at different temperatures (denoted in parentheses, in °C), the catalytic performance decreased in the sequence of Fe-ZSM-5 (700) > Fe-ZSM-5 (600) > Fe-ZSM-5 (500), Fe-ZSM-5 (400), Fe-ZSM-5 (350). Among different Fe-zeolite catalysts prepared by subliming at 700°C, the catalytic performance decreased in the sequence of Fe-ZSM-5 > Fe-MOR > Fe-FER > Fe-Beta > Fe-Y which are similar to the Fe-zeolites prepared by aqueous ion-exchange method. The activity for the SCR (selective catalytic reduction) of NO with ammonia was also investigated on different Fe-zeolites. The FT-IR results supported the two-step mechanism: NO is an intermediate for N₂ formation, NH₃ was first oxidized to NO by O₂, NO then reacts to the unreacted NH ₃ to produce N₂.