Experimental study on selective catalytic reduction of NO by C₃H₆ over Fe-Ag/Al₂O₃ catalysts

Sol-gel and impregnation methods were used to prepare the Fe/Ag/Al₂O₃ catalysts supported on the monolithic cordierite with different Fe/Ag loading ratios. The catalytic performance to reduce NO with C₃H₆ was evaluated in a one-dimensional electrically heated temperature programmed ceramic tubular reactor in simulated flue gas atmosphere at 200-700 ℃. The results show that the NO reduction efficiency on 7.2Fe/1.9Ag/20Al₂O₃/CM with C₃H₆ is more than 90% and reaches about 100% at the temperatures of 500 ℃ and 550 ℃ respectively. Iron can effectively improve the ability of Ag/20Al₂O₃/CM catalysts to resist SO₂ and H₂O in flue gas. When SO₂ and H₂O are 0.02% and 8% in the flue gas, the NO reduction efficiency is almost not influenced on 7.2Fe/1.9Ag/20Al₂O₃/CM at 500 ℃. The 90% NO reduction efficiency is maintained during 6 h without decrease. However, the catalytic activity of 2Ag/20Al₂O₃/CM without iron modification is strongly influenced by SO₂ and H₂O in the flue gas. The NO reduction efficiency on Ag/20Al₂O₃/CM decreases rapidly from about 70% to 46% and 25% respectively, when the SO₂ and H₂O are 0.02% and 8% in the flue gas. The results of XRD and SEM of the catalyst show that AgFeO₂ and Fe³⁺ are formed in the 7.2Fe/1.9Ag/20Al₂O₃/CM catalyst after the modification by iron, and the surface of the catalyst become loose and porous, forming Fe₃O₄-based needle-like and flaky crystals. H₂-TPR results show that 7.2Fe/1.9Ag/20Al₂O₃/CM has better reduction properties than Ag/20Al₂O₃/CM in the wider temperature range. Pyridine adsorption Infrared Spectroscopy (Py-FTIR) experimental results show that Fe increases the Lewis acid sites in the catalyst surface.