Novel Methods for Assessing the SO2 Poisoning Effect and Thermal Regeneration Possibility of MOx–WO3/TiO2 (M = Fe, Mn, Cu, and V) Catalysts for NH3-SCR

In this study, the sulfur resistance and thermal regeneration of a series of MO_x-WO₃/TiO₂ (denoted as MW/Ti, M = Fe, Mn, Cu, V) catalysts were investigated. After in situ sulfur poisoning, the selective catalytic reduction (SCR) activity of the poisoned catalysts was inhibited at low temperatures but was promoted at high temperatures. After thermal regeneration, the FeW/Ti catalyst was more thoroughly regenerated among nonvanadium-based catalysts. To investigate the impacts of sulfur poisoning, characterizations including X-ray diffraction, thermogravimetric analysis, H₂ temperature-programmed reduction, and SO₂ temperature-programmed desorption were applied. It was discovered that different sulfur-containing species blocked the adsorption of NH₃/NO to a distinct extent over all of the catalysts, thus affecting the catalytic activity. The effect depends on which are dominant (NO or NH₃) during the reaction at different temperatures. The difference in regeneration depends on the formation of sulfate species. The ratio of M_x(SO₄)_y to NH₄HSO₄ generated on the catalysts was adopted to assess the possibility of regeneration. The ratios were 0.5, 1.4, 1.5, and 1.7 for VW/Ti, FeW/Ti, CuW/Ti, and MnW/Ti catalysts, respectively. The lower the ratio was, the easier the catalyst could be regenerated. Meanwhile, the sulfate species could be decomposed more easily on the poisoned FeW/Ti catalyst. FeW/Ti is an excellent candidate for low- and medium-temperature NH₃-SCR among nonvanadium-based catalysts.