The recycle of red mud as excellent SCR catalyst for removal of NOx

Abstract

The development of new routes for the utilization of red mud (RM) waste is very urgent due to its huge accumulation and potential environmental harm. By taking advantage of its Fe–Al–Si–Ti composition and excellent plasticity, we developed a ball milling and acid–base neutralization method to reuse the RM waste as Fe-based denitration catalysts. The resulting RM catalysts demonstrate excellent catalytic activity and stability with >90% NO conversion above 400 °C in the presence of SO₂ and H₂O, which is even much better than that of a commercial V–W–Ti catalyst. Characterization data reveal that our treatment eliminates poisonous alkaline metal elements and increases dispersion of RM particles, making the RM active for denitration reactions. The formation of ferric sulfate species with more reducible Fe³⁺/Fe²⁺ active sites by a SO₂ activation method can further enhance the denitration activity. Moreover, NH₃-TPD and in situ IR results demonstrate that the NH₃-SCR reaction over the RM catalyst follows the Eley–Rideal mechanism at high temperature and the increased absorption of NH₃ for alkaline metal-eliminated or SO₂-activated samples accounts for its high DeNO_x efficiency. The demonstrated feasibility for reusage of the RM as DeNO_x catalyst has promising industrial prospects for its extremely low cost, no toxicity, and high efficiency.