Modulating NH3 oxidation and inhibiting sulfate deposition to improve NH3-SCR denitration performance by controlling Mn/Nb ratio over MnaNbTi2Ox (a = 0.6-0.9) catalysts

Abstract

The Mn_aNbTi₂O_x (a = 0.6-0.9) catalysts for NH₃ selective catalytic reduction denitration were prepared using the co-precipitation method. Among them, Mn_0.7NbTi₂O_x exhibits well low-temperature catalytic performance, wide activity temperature range (180-480 ℃), and worthy resistance to SO₂ even with H₂O. XRD was used to investigate the structure of Mn_aNbTi₂O_x, in which Mn and Nb oxides highly dispersed in the Mn_aNbTi₂O_x catalysts and Nb can dope into the crystal lattice of TiO₂. XRF and XPS results show Nb can affect the transfer of electrons to Mn⁴⁺, and changing the Mn/Nb ratio can regulate the Mn⁴⁺ content on the Mn_aNbTi₂O_x catalysts. H₂-TPR, NH₃ and NO oxidation results verify that Nb inhibits the oxidation capacity of Mn_aNbTi₂O_x, and altering the Mn/Nb ratio can get appropriate oxidation property, which facilitates low-temperature NH₃ activation and limit non-selective oxidation for NH₃. In-situ DRIFTS results show Nb-OH bonds can provide new Brønsted acid sites, and both Lewis and Brønsted acid sites are active. Furthermore, Nb addition prevents sulphate deposition on the catalyst. The effect of Mn/Nb on catalytic performance, N₂O formation and inhibition, SO₂ poisoning, SO₂ effect on NH₃-SCR, and the enhancement of SO₂ tolerance are also analyzed.