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

Abstract

Low N2 selectivity and SO2 resistance of Mn-based catalysts for removal of NO x 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.

Rationally Designed Confined Structure Ce-Mn-TNTs Catalyst for Low-Temperature NH3-SCR Reaction with Superior Activity and H2O/SO2 Tolerance

“…In addition, several weak peaks occurred due to SO 2 being adsorbed on the catalyst surface. The peak at 1330 cm –1 corresponded to the asymmetric tensile vibration of OSO in sulfate, the peak at 1371 cm –1 was attributed to the trigeminal surface sulfate, while the peak at 1176 cm –1 was related to the formation of sulfate species. ,− The above phenomenon indicated that there was a competitive adsorption of NO and SO 2 on the catalyst surface. According to the peak intensity, it was seen that NO was mainly adsorbed on the surface of the Ce-Mn-TNT catalyst at 50 °C.…”

A Novel MnOx–MoOx Codoped Iron-Based Catalyst for NH3-SCR with Superior Catalytic Activity over a Wide Temperature Range

“…The peak at 355 °C resulted from the reduction of Fe 2 O 3 to Fe 3 O 4 . A wide peak around 523 °C can be regarded as a simultaneous reduction of MnO and Fe 3 O 4 . , In the case of the MFMo 4 catalyst, there was an upward shift of the reduction temperature, which implied that a strong interaction occurred between the inclusion of MoO x and Mn and Fe. Upon considering the XPS results, it is evident that the incorporation of MoO x exerted a detrimental impact on the redox property of the MF catalyst.…”

Design Strategy of the MnOx Catalyst for SCR of NO with NH3: Mechanism of Lead Poisoning and Improvement Method

“…Commonly, the oxidation of NH 3 is considered to be the primary reason leading to the formation of N 2 O. Based on previous findings, the formation of N 2 O could be attributed to three main pathways: the reaction between NH 3 and the introduced oxygen; the reaction between NH 3 and the lattice oxygen of the catalyst; and the SCR reaction (NO + O 2 + NH 3 ) . These pathways are often associated with the excessive oxidative capability of pure MnO x catalysts, resulting in decreased N 2 selectivity.…”

“…Based on our previous studies, a novel core–shell structure MnO x -SiO 2 catalyst with greatly improved N 2 selectivity and SO 2 resistance was synthesized . However, its practical efficacy in the presence of Pb-containing flue gas remains unexplored, and a comprehensive understanding of the underlying mechanism is still lacking.…”