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.