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

Hematite (α - Fe 2 O 3 ) is a promising candidate for NH 3 selective catalytic reduction (NH 3 -SCR) of NO x due to its good sulfur resistance. However, the activity of pure α - Fe 2 O 3 is very low. In this work, α - Fe 2 O 3 obtained excellent N 2 selectivity and medium–high temperature activity via a simple surface sulfation method. The α - Fe 2 O 3 -350 (sulfated at 350 °C) sample showed an NO conversion rate of ~ 100% in the range of 275–350 °C and exhibited excellent H 2 O and SO 2 resistance ability at 300 °C. Furthermore, pure α-Fe 2 O 3 was used as a model catalyst to fully uncover the effect of sulfation on FeO x -based catalysts in NH 3 -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 - Fe 2 O 3 changed from surface sulfates to bulk-like sulfates. Although sulfation treatment reduced the redox properties of α - Fe 2 O 3 , 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 x on the α - Fe 2 O 3 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.