Poisoning effect of SO₂ on Mn-Ce/TiO₂ catalysts for NO reduction by NH₃ at low temperature

Effects of SO₂ on performance of Mn-Ce/TiO₂ catalysts were investigated in the selective catalytic reduction of NO with NH₃.The catalysts were characterized by BET surface area, X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), respectively.The results show that SO₂ has inhibitory effect on the selective catalytic reduction (SCR), and NO_x conversion decreases from 84% to 42% at 140℃.This is mainly because the presence of SO₂ results in the decrease of the specific surface area of the catalysis and the pore size distribution of 5-10 nm.SO₂ can cause TiO₂ transformation from anatase to rutile phase, the crystallization phenomenon of active components MnO_x, and the decrease of the strong interaction between Mn and Ti.The variations of physical and chemical properties of poisoned Mn-Ce/TiO₂ catalyst block the O₂^-→O^-→O^2- conversion path, which reduces the proportion of higher catalytic activity component MnO₂ in MnO_x, weakens oxygen storage ability of CeO_x, and accumulates absorbed oxygen on the catalyst surface decreasing the adsorption and desorption of NO on active sites.Ammonium sulfate formed on the catalyst surface covers the Lewis acid sites and decreases the adsorption amount of NH₃.