Understanding the dual-acting of iron and sulfur dioxide over Mn-Fe/AC catalysts for low-temperature SCR of NO

Abstract

Poor N2 selectivity and low SO2-tolerant are dominated weaknesses for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) catalysts, which must be overcome for practical applications. Herein, a Mn-Fe mixed catalyst supported on active carbon (Mn-Fe/AC) for low-temperature NH3-SCR of NO was prepared, and the influence of SO2 on this process was also studied. Both iron and sulfur dioxide exhibited a dual-acting over Mn-Fe/AC catalyst for NH3-SCR of NO. Sulfur dioxide had two effects when SO2 was introduced in the feed gas under SCR conditions, including inhibiting the low temperature activity of the catalysts and improving N2 selectivity which exceeded 90% during the whole testing temperature. The introduction of SO2 could promote the formation of NH2NO which was the main intermediate and then decomposed into N2. Fe species in Mn-Fe/AC catalyst could improve N2 selectivity. In the presence of SO2, it showed considerable SO2 resistance compared to Mn/AC catalyst. On the one hand, iron species improved the selectivity through forming new active sites promoting the formation of NH2NO and suppressing the free NO3- generation. On the other hand, iron existing in Mn-Fe/AC catalyst could decrease the amount of sulfur species adsorbent and SO2 oxidation, thereby exhibiting better SO2 resistance.