A comparative study of Zr, Al or Sr doped Mn/MCM-41 for NH3-SCR and resistance to SO2/H2O

Abstract

In this paper, the effects of Zr, Al or Sr doped Mn/MCM-41 on NH₃-SCR activity, SO₂/H₂O resistance and mechanism were studied. The results showed that Mn/Zr-MCM-41 has 100% NO_x conversion at 175–300 °C while Mn/Al-MCM-41 achieves about 94% N₂ selectivity at 120–400 °C. Zr doping significantly enhances the resistance to SO₂ at 200 °C while Sr plays a negative role. Doped metal does not change the ordered hexagonal arrangement of MCM-41, but can cause the specific surface area enrichment of Mn while Al doping leads to the entry of Mn into the channel of MCM-41. Mn/MCM-41 has only Lewis acid sites, but Zr, Al or Sr doped catalysts have Lewis and Brønsted acid sites. Moreover, the reaction path on Mn/MCM-41 and Mn/Zr-MCM-41 mainly conforms to the L–H mechanism while Mn–Al or Mn–Sr doped catalysts follow L–H and E–R mechanisms. However, the deposited sulfates change the progress of the NH₃-SCR process and cause a decline of SCR activity.