Catalytic performance of Fe-ZSM-5 catalysts for selective catalytic reduction of nitric oxide by ammonia

A series of Fe-exchanged molecular sieves were studied as catalysts for the SCR of NO with ammonia. Fe-ZSM-5 and Fe-mordenite catalysts were highly active for the SCR reaction. Nearly 100% NO conversions were obtained at 400°-500°C under conditions with a high space velocity (GHSV = 4.6 × 10⁵L/hr). Fe-Y(Si/Al = 2.4) and Fe-MCM-41 (Si/Al =10) with larger pore diameters showed lower activities for this reaction. For Fe-ZSM-5 catalysts, the SCR activity also decreased with increasing Si/Al ratio in the zeolites. As compared with the commercial vanadia catalyst, the Fe-ZSM-5(10) catalysts were much more active. They functioned in a broader temperature window and produced only N₂(rather than N₂O) and H₂O. A substantially lower activity for SO₂oxidation to SO₃was also observed.