The dual effects of ammonium bisulfate on the selective catalytic reduction of NO with NH3 over Fe2O3-WO3 catalyst confined in MCM-41

Ammonium bisulfate (ABS) has long been considered as a main poisoning material in the selective catalytic reduction by NH3 (NH3-SCR) due to the inevitable coverage of sticky ABS on catalytic active sites in sulfur-containing atmospheres, which severely hinders the achievement of stable and highly active NH3-SCR catalysts. In the present study, we report a novel observation of the dual effects of ABS on the NH3-SCR reaction. That is, ABS inhibits the NH3-SCR performance of Fe2O3-WO3/MCM-41 catalyst at low temperatures (50-200 degrees C) but shows apparent and sustainable reaction promotion when the temperature surpasses 250 degrees C. X-ray photoelectron spectroscopy (XPS) and NO probing adsorption confirmed that when ABS is deposited on the catalyst surface, a partial interaction between ABS and the Fe2O3-WO3 component occurs, resulting in blocking of the active sites and an obvious loss of catalytic activity. With increasing reaction temperature, the ammonium in ABS can be facilely consumed by NO/O-2, thus inducing the disintegration of poisoning species. The sulfate group transforms into metal sulfate and survives at high temperatures. Importantly, owing to the strong inductive effect of sulfate species, both the acidity and redox properties of the catalyst are greatly improved, which contributes to the enhanced activity. The results of the present study expand our knowledge of the role of ABS in the NH3-SCR reaction and will be useful for designing high-performing NH3-SCR catalysts.