Mechanism of SO₂/H₂O enhanced rare earth tailings catalysts in NH₃-SCR at medium and high temperature

Rare earth tailings (RET) NH3-SCR catalysts were prepared by mechanical and microwave activation of a large amount of rare earth tailings after beneficiation of Bayan Ebo rare earth ore. The effects of SO2/H2O on the denitrification performance of the RET catalysts were evaluated by conducting denitrification activity tests, SO2/H2O tolerance tests and in situ DRIFTs mechanistic analysis. The results showed that the denitrification activity was significantly increased in the presence of SO2/H2O. And in situ DRIFTs analysis showed that in the presence of SO2/H2O, SO2 could be adsorbed as SO32- groups by the hydroxyl groups on the catalyst surface and react with SO42- to form S2O72- species. And in the presence of NH3, S2O72- would decompose into unstable SO42- species and SO32- and continue to react cyclically to form S2O72- species, providing the RET catalyst provides more acid sites, facilitating the SCR reaction.