Unveiling the SO 2 Resistance Mechanism of a Nanostructured SiO 2 ( x )@Mn Catalyst for Low-Temperature NH 3 -SCR of NO.

Low N selectivity and SO resistance of Mn-based catalysts for removal of NO at low temperatures by NH-SCR (selective catalytic reduction) technology are the two main intractable problems. Herein, a novel core-shell-structured SiO@Mn catalyst with greatly improved N selectivity and SO resistance was synthesized by using manganese carbonate tailings as raw materials. The specific surface area of the SiO@Mn catalyst increased from 30.7 to 428.2 m/g, resulting in a significant enhancement in NH adsorption capacity due to the interaction between Mn and Si. Moreover, the NO formation mechanism, the anti-SO poisoning mechanism, and the SCR reaction mechanism were proposed. NO originated from the reaction of NH with O and the SCR reaction, as well as from the reaction of NH with the chemical oxygen of the catalyst. Regarding improving the SO resistance, DFT calculations showed that SO was observed to preferentially adsorb onto the surface of SiO, thus preventing the erosion of active sites. Adding amorphous SiO 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 NO. This strategy is expected to assist in designing an effective Mn-based catalyst for low-temperature NH-SCR of NO.