Selective catalytic oxidation (SCO) of ammonia to nitrogen over Fe-exchanged zeolites

Fe-exchanged zeolites were prepared and studied as catalysts for selective catalytic oxidation (SCO) of ammonia to nitrogen in the presence of excess oxygen. Fe-ZSM-5, Fe-mordenite (MOR), and Fe-clinoptilolite (HEU) showed excellent SCO performance at a very high space velocity (GHSV = 2.3 x 10(5) h(-1)). Greater than 97% NH3 conversion and nearly 100% N-2 selectivity were obtained. Among different zeolites, the catalytic performance decreased in the sequence of Fe-ZSM-5, Fe-MOR, Fe-HEU > Fe-Y, Fe-Beta > Fe-ferrierite, Fe-chabazite. High iron content, low Si/Al ratio, and low ammonia concentration were favorable for high activities for NH3 oxidation to N-2. For the Fe-exchanged zeolites, there existed a good correlation between the N-2 selectivity for the SCO reaction and the activity for the SCR (selective catalytic reduction) of NO with ammonia; i.e., the higher the SCR activity, the higher the N-2 selectivity in SCO. The variable valence of iron cations might be beneficial to oxygen activation and thus result in the high SCO performance for the Fe-exchanged zeolites. A kinetic study indicated that the reaction was first order with respect to NH3 and the apparent reaction activation energy (E-a) was 88 kJ/mol. (C) 2001 Academic Press