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 Fe2O3 catalysts were synthesized using the homogeneous precipitation method and subjected to laboratory evaluation for selective catalytic reduction of NOx with NH3 (NH3-SCR). The best Fe0.75V0.25O delta catalyst with a Fe/V mole ratio of 3/1 exhibited superior catalytic performance, achieving 100% NOx conversion at 200 degrees C over a wide temperature window from 175 to 400 degrees C, believed to be the best Fe -based low-temperature NH3-SCR catalyst identified to date. The Fe0.75V0.25O delta catalyst also showed prominent resistance to high gas hourly space velocity (GHSV; 200 000 h(-1)) and strong durability to SO2 and H2O. 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 FeVO4 and Fe2O3. 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 NO2. Meanwhile, the strong interaction between FeVO4 and Fe2O3 species kept V at a higher valence, beneficial for the adsorption and activation of NH3. The synergistic effect of FeVO4 and Fe2O3 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 degrees C, since the consumption of adsorbed NH3 species could be divided into the explicit "standard SCR" and "fast SCR" stages, while an Eley-Rideal mechanism proceeded dominantly at and above 200 degrees C, in which the adsorbed NH3 species were eliminated by gaseous NO directly and linearly. Both the Bronsted and Lewis acid sites played equivalently significant roles in NH3-SCR reaction.