Inductive Effect Boosting Catalytic Performance of Advanced Fe1–xVxOδ Catalysts in Low-Temperature NH₃ Selective Catalytic Reduction: Insight into the Structure, Interaction, and Mechanisms

A series of vanadium doped Fe 2 O 3 catalysts were synthesized using the homogeneous precipitation method and subjected to laboratory evaluation for selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). The best Fe 0.75 V 0.25 O δ catalyst with a Fe/V mole ratio of 3/1 exhibited superior catalytic performance, achieving 100% NO x conversion at 200 °C over a wide temperature window from 175 to 400 °C, believed to be the best Fe-based low-temperature NH 3 -SCR catalyst identified to date. The Fe 0.75 V 0.25 O δ catalyst also showed prominent resistance to high gas hourly space velocity (GHSV; 200 000 h –1 ) and strong durability to SO 2 and H 2 O. Doping of V was shown to remarkably boost the catalytic activity, due to enhancement of the redox ability and surface acidity. XRD, Raman, and morphology results revealed that the incorporation of V had led to the formation of amorphous FeVO 4 and Fe 2 O 3 . Coupling XPS and UV–vis diffuse reflectance spectra (DRS) results with DFT, it was discovered that the electron inductive effect between Fe and V generated the charge depletion of Fe, resulting in an improvement of the redox ability, facilitating the oxidation of NO to NO 2 . Meanwhile, the strong interaction between FeVO 4 and Fe 2 O 3 species kept V at a higher valence, beneficial for the adsorption and activation of NH 3 . The synergistic effect of FeVO 4 and Fe 2 O 3 thus improved the low-temperature catalytic activity and lowered the apparent activation energy. Combining in situ diffusion Fourier transform infrared spectroscopy (DRIFTS) results with reaction kinetic studies, it was concluded that the SCR reaction mainly followed the Langmuir–Hinshelwood mechanism below 200 °C, since the consumption of adsorbed NH 3 species could be divided into the explicit “standard SCR” and “fast SCR” stages, while an Eley–Rideal mechanism proceeded dominantly at and above 200 °C, in which the adsorbed NH 3 species were eliminated by gaseous NO directly and linearly. Both the Brønsted and Lewis acid sites played equivalently significant roles in NH 3 -SCR reaction.