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

Hematite (alpha-Fe2O3) is a promising candidate for NH3 selective catalytic reduction (NH3-SCR) of NOx due to its good sulfur resistance. However, the activity of pure alpha-Fe2O3 is very low. In this work, alpha-Fe2O3 obtained excellent N-2 selectivity and medium-high temperature activity via a simple surface sulfation method. The alpha-Fe2O3-350 (sulfated at 350 degrees C) sample showed an NO conversion rate of similar to 100% in the range of 275-350 degrees C and exhibited excellent H2O and SO2 resistance ability at 300 degrees C. Furthermore, pure alpha-Fe2O3 was used as a model catalyst to fully uncover the effect of sulfation on FeOx-based catalysts in NH3-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 alpha-Fe2O3 changed from surface sulfates to bulk-like sulfates. Although sulfation treatment reduced the redox properties of alpha-Fe2O3, it significantly increased its surface acidity and thus the activity. Excessive bulk-like sulfates induced a decrease in activity. Sulfation inhibited the adsorption of NOx on the alpha-Fe2O3 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. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

In this study, the activity and selectivity of hematite were improved via surface sulfation, with moderate sulfate species enhancing activity while excessive sulfates decreasing it, ultimately inhibiting the Langmuir-Hinshelwood mechanism in NH3-SCR reactions.