Sulfur resistance of Ce-Mn/TiO₂ catalysts for low-temperature NH₃-SCR

Ce-Mn/TiO₂ catalyst prepared using a simple impregnation method demonstrated a better low-temperature selective catalytic reduction of NO with NH₃ (NH₃-SCR) activity in comparison with the sol-gel method. The Ce-Mn/TiO₂ catalyst loading with 20% Ce had the best low-temperature activity and achieved a NO conversion rate higher than 90% at 140-260°C with a 99.7% NO conversion rate at 180°C. The Ce-Mn/TiO₂ catalyst only had a 6% NO conversion rate decrease after 100 ppm of SO₂ was added to the stream. When SO₂ was removed from the stream, the catalyst was able to recover completely. The crystal structure, morphology, textural properties and valence state of the metals involving the novel catalysts were investigated using X-ray diffraction, N₂ adsorption and desorption analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy, respectively. The decrease of NH₃-SCR performance in the presence of 100 ppm SO₂ was due to the decrease of the surface area, change of the pore structure, the decrease of Ce⁴⁺ and Mn⁴⁺ concentration and the formation of the sulfur phase chemicals which blocked the active sites and changed the valence status of the elements.