Insight into the enhanced catalytic activity and H₂O/SO₂ resistance of MnFeO_x/Defect-Engineered TiO₂ for low-temperature selective catalytic reduction of NO with NH₃

A series of Mn-Fe mixed oxide (MnFeO_x) supported on high-surface-area TiO₂ (Ti_ov) containing engineered Ti³⁺/oxygen vacancies was demonstrated for NH₃-SCR of NO. The best catalyst MnFe/Ti_ov(0.05)-1 exhibited excellent NH₃-SCR activity (>99 % conversion) over 60–260 °C and superior resistance to high H₂O content (20 vol%), with NO conversion exceeding 90 % at temperatures lower than 150 °C. Furthermore, MnFe/Ti_ov(0.05)-1 exhibited outstanding durability over 70 h of sustained operation in the co-presence of H₂O and SO₂, whereas catalytic deactivation was observed for the conventional TiO₂-supported catalyst (MnFe/Ti). The combined results of various characterization techniques confirmed that the interactions between the MnFeO_x and Ti_ov supports were strengthened. The defect-rich surface of the Ti_ov support promoted the dispersion of MnFeO_x and facilitated the redox cycle Mn⁴⁺ + Ti³⁺ ↔ Mn³⁺ + Ti⁴⁺, thus facilitating the adsorption and activation of NH₃ and NO molecules. Moreover, the in situ diffuse reflectance infrared Fourier transform results indicated that H₂O strongly suppressed the adsorption/activation of NH₃ and NO_x and the reactions between NH₃ and NO_x through the Langmuir–Hinshelwood pathway on MnFe/Ti, while such adverse effects were significantly reduced when using MnFe/Ti_ov(0.05)-1, in which the Eley–Rideal mechanism was dominant.