Study of SO2 effect on selective catalytic reduction of NOx with NH3 over Fe/CNTs: The change of reaction route

摘要

Fe/CNTs catalyst exhibits perfect performance when it is used in selective catalytic reduction of NOx with NH3 (NH3-SCR), meeting the requirements of low-temperature conversion and no vanadium use, which is thought to be a potential candidate for traditional V2O5-WO3 (MoO3)/TiO2 catalysts. However, small amount of SO2 remained after the desulfurization process severely impacts the activity of Fe/CNTs. TGA, XPS and TPD tests were used to investigate the properties of SOx-species formed on the catalysts; TPSR tests were proceeded to reveal the difference of reaction pathway between normal SCR reaction and that in presence of SO2. The results showed that ferric sulfate was the major sulfate species accumulated on Fe/CNTs, which enhanced the adsorption of NH3 species while constrained the adsorption of NOx species. Reaction pathway study suggested the adsorption and activation of NOx species over Fe/CNTs were conductive to the formation of intermediates which was the key to its excellent low-temperature performance. While this effective reaction pathway was inhibited with SO2 in the feed gas and led to the low-temperature activity loss ( 275 degrees C). Instead, ferric sulfates formed on Fe/CNTs promoted the reaction between adsorbed NH3 species and gaseous NO through which SCR performance at higher reaction temperature was promoted and this became the dominating reaction pathway. The transform of dominating reaction route was the reason for the change of de-NOx performance over Fe/CNTs in presence of SO2.