Enhancement of low-temperature activity of γ-Fe₂O₃-modified V₂O₅-MoO₃/TiO₂ catalysts for selective catalytic reduction of NO_x with NH₃

In this study, a series of γ-Fe₂O₃-modified V₂O₅-MoO₃/TiO₂ (VMT) catalysts was prepared by wet impregnation method. The γ-Fe₂O₃-modified catalysts exhibited excellent catalytic performance, and 1.25 wt% γ-Fe₂O₃ content improved the deNO_x efficiency at 150 °C from 54% (unmodified VMT catalyst) to 84% (modified catalyst). BET, XRD, XPS, NH₃-TPD, H₂-TPR, and in situ DRIFTs were employed to characterize the physicochemical properties and reaction mechanisms of the catalysts. The introduction of γ-Fe₂O₃ increased the V⁵⁺/V⁴⁺ ratio, surface chemisorbed oxygen content, redox ability, and a number of acid sites in the prepared catalysts. XPS confirmed the addition of γ-Fe₂O₃ introduced new charge transfer pathways (Fe³⁺/Fe²⁺ ↔ V⁵⁺/V⁴⁺). In situ DRIFTs suggested that the addition of γ-Fe₂O₃ to the catalyst significantly increased the adsorption capacity of catalyst for NH₃ and NO_x, while also exerting a strong activating effect on the adsorbed NH₃. Furthermore, selective catalytic reduction over the VMT and 5PEG@1.25Fe-VMT catalysts followed the Eley-Rideal (E-R) mechanism. At temperatures above 200 °C, the 5PEG@1.25Fe-VMT catalyst also followed the Langmuir-Hinshelwood (L-H) mechanism.