Mesoporous Mn–Ti amorphous oxides: a robust low-temperature NH3-SCR catalyst

Abstract

A series of mesoporous Mn–Ti amorphous oxides (Mn_aTi_1−a) fabricated by a combined strategy of in situ deposition and freeze-drying were studied for the selective catalytic reduction of NO with NH₃ (NH₃-SCR) at low temperature. The physico-chemical properties of Mn_aTi_1−a catalysts were characterized systematically by XRD, TEM, Raman, EXAFS, N₂-sorption, XPS, H₂-TPR and NH₃-TPD. The results revealed that the increased amount of Mn⁴⁺ species greatly promoted the NO conversion at low temperature. Additionally, the highly dispersed active sites, abundant surface Lewis acid sites and strong interaction between Mn and Ti contributed to the remarkable low-temperature SCR activity. Among these Mn_aTi_1−a catalysts, the Mn_0.5Ti_0.5 catalyst exhibited the best low-temperature NH₃-SCR performance (61% NO conversion at 100 °C and over 95% N₂ selectivity at 150–250 °C) and excellent H₂O/SO₂ durability. In situ FTIR was used to investigate the reaction mechanism, and the results indicated that both the L–H and E–R mechanisms were present and NH₃-SCR mainly proceeded via the L–H reaction pathway at low temperature.