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

Abstract

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.