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 the 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 (XRD), N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), 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.