Effects of sulfation on hematite for selective catalytic reduction of nitrogen oxides with ammonia.

Hematite (α-FeO) is a promising candidate for NH selective catalytic reduction (NH-SCR) of NO due to its good sulfur resistance. However, the activity of pure α-FeO is very low. In this work, α-FeO obtained excellent N selectivity and medium-high temperature activity via a simple surface sulfation method. The α-FeO-350 (sulfated at 350 °C) sample showed an NO conversion rate of ~ 100% in the range of 275-350 °C and exhibited excellent HO and SO resistance ability at 300 °C. Furthermore, pure α-FeO was used as a model catalyst to fully uncover the effect of sulfation on FeO-based catalysts in NH-SCR reactions. Structural characterization indicated that the degree of surface sulfation of the catalyst would be deepened with increasing temperature, and the states of sulfate species on α-FeO changed from surface sulfates to bulk-like sulfates. Although sulfation treatment reduced the redox properties of α-FeO, it significantly increased its surface acidity and thus the activity. Excessive bulk-like sulfates induced a decrease in activity. Sulfation inhibited the adsorption of NO on the α-FeO catalyst surface and reduced the thermal stability of nitrates at medium-high temperature. Thus, the Langmuir-Hinshelwood (L-H) mechanism was inhibited, and the reaction mainly followed the Eley-Rideal (E-R) mechanism.