Unveiling the SO<sub>2</sub> Resistance Mechanism of a Nanostructured SiO<sub>2</sub>(<i>x</i>)@Mn Catalyst for Low-Temperature NH<sub>3</sub>-SCR of NO
Hongli Wu, Weizao Liu, Xiaoyong Jiang, Ya Liang, Yang Chen, Jun Cao, Qingcai Liu
Abstract
Low N 2 selectivity and SO 2 resistance of Mn-based catalysts for removal of NO x at low temperatures by NH 3 -SCR (selective catalytic reduction) technology are the two main intractable problems. Herein, a novel core–shell-structured SiO 2 @Mn catalyst with greatly improved N 2 selectivity and SO 2 resistance was synthesized by using manganese carbonate tailings as raw materials. The specific surface area of the SiO 2 @Mn catalyst increased from 30.7 to 428.2 m 2 /g, resulting in a significant enhancement in NH 3 adsorption capacity due to the interaction between Mn and Si. Moreover, the N 2 O formation mechanism, the anti-SO 2 poisoning mechanism, and the SCR reaction mechanism were proposed. N 2 O originated from the reaction of NH 3 with O 2 and the SCR reaction, as well as from the reaction of NH 3 with the chemical oxygen of the catalyst. Regarding improving the SO 2 resistance, DFT calculations showed that SO 2 was observed to preferentially adsorb onto the surface of SiO 2, thus preventing the erosion of active sites. Adding amorphous SiO 2 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 2 . This strategy is expected to assist in designing an effective Mn-based catalyst for low-temperature NH 3 -SCR of NO.