FeSTi Superacid Catalyst for NH3-SCR with Superior Resistance to Metal Poisons in Flue Gas

Abstract

At present, commercial V2O5–WO3(MoO3)/TiO2 catalyst for selective catalytic reduction with NH3 (NH3-SCR) shows poor resistance to alkali, alkaline-earth, and heavy metals that are normally contained in flue gas. The present work demonstrated a solid superacid FeSTi catalyst prepared using a thermal hydrolysis method that exhibited greatly improved resistance to poisoning by K, Ca, and Pb. This FeSTi catalyst provided high NOx conversion (>90%) over a wide temperature range even after being doped with 1 wt % K2O, 2 wt % CaO, or 5 wt % PbO. Characterizations of the catalysts indicated that the deposition of metal oxides did not affect the stability of their crystal structures or redox properties. K2O, CaO, and PbO were evidently trapped by surface SO42– ions on the catalyst to form K2SO4, CaSO4, and PbSO4. The FeSTi catalyst contained approximately 4.1 wt % S, and this high S content allowed the catalyst to retain superacid properties following metal oxide deposition, such that its catalytic activity was not significantly affected. In situ diffuse reflectance infrared Fourier transform spectroscopy data indicated that both the Eley–Rideal (E–R) and Langmuir–Hinshelwood reaction mechanisms simultaneously occurred over the catalyst. The deposition of oxide poisons did not change the reaction routes or mechanisms, although the reaction rate associated with the E–R mechanism was slowed.