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 ex cellent 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 concentra tion were favorable for high activities for NH3 oxidation to N-2. For the F e-exchanged zeolites, there existed a good correlation between the N-2 sele ctivity for the SCO reaction and the activity for the SCR (selective cataly tic reduction) of NO with ammonia; i.e., the higher the SCR activity, the h igher the N-2 selectivity in SCO. The variable valence of iron cations migh t be beneficial to oxygen activation and thus result in the high SCO perfor mance for the Fe-exchanged zeolites. A kinetic study indicated that the rea ction was first order with respect to NH3 and the apparent reaction activat ion energy (E-a) was 88 kJ/mol. (C) 2001 Academic Press