Unveiling the SO₂ Resistance Mechanism of a Nanostructured SiO₂(x)@Mn Catalyst for Low-Temperature NH₃-SCR of NO

Low N₂ selectivity and SO₂ resistance of Mn-based catalysts for removal of NO at low temperatures by NH₃-SCR (selective catalytic reduction) technology are the two main intractable problems. Herein, a novel core-shell-structured SiO₂@Mn catalyst with greatly improved N₂ selectivity and SO₂ resistance was synthesized by using manganese carbonate tailings as raw materials. The specific surface area of the SiO₂@Mn catalyst increased from 30.7 to 428.2 m²/g, resulting in a significant enhancement in NH₃ adsorption capacity due to the interaction between Mn and Si. Moreover, the N₂O formation mechanism, the anti-SO₂ poisoning mechanism, and the SCR reaction mechanism were proposed. N₂O originated from the reaction of NH₃ with O₂ and the SCR reaction, as well as from the reaction of NH₃ with the chemical oxygen of the catalyst. Regarding improving the SO₂ resistance, DFT calculations showed that SO₂ was observed to preferentially adsorb onto the surface of SiO₂, thus preventing the erosion of active sites. Adding amorphous SiO₂ can transform the reaction mechanism from Langmuir-Hinshelwood (L-H) to Eley-Rideal (E-R) by adjusting the formation of nitrate species to produce gaseous NO₂. This strategy is expected to assist in designing an effective Mn-based catalyst for low-temperature NH₃-SCR of NO.