In situ DRIFTS FT-IR and DFT study on Fe-V-W/Ti removal of NOx and VOCs

Nitrogen oxides (NO_X) and volatile organic compounds (VOCs) are generated during the coal-fired power plant’s combustion. They can be simultaneously removed in SCR (selective catalytic reduction) region. Herein, the performance of V-W/Ti and Fe-V-W/Ti synthesized by wet impregnation in removing NO_X and VOCs was evaluated. XPS (X-ray photoelectron spectroscopy) result indicated that a redox cycle of Fe²⁺ + V⁵⁺ ⇌ Fe³⁺ + V⁴⁺ could form electron vacancy through electron transfer. Besides, the mechanisms of NH₃-SCR and VOCs catalytic oxidation were explored with in situ DRIFTS experience and DFT calculation. On Fe-V-W/Ti, in situ DRIFTS study found more absorption sites of NH₃, and different intermediates during simultaneously removal process. DFT calculation demonstrated that absorption energy of O₂ was decreased and O = O bond was lengthened with Fe doped. Both V-W/Ti and Fe-V-W/Ti followed the L–H mechanism and shared a common NH₃-SCR pathway: \({NO\left(g\right)+\frac{1}{2}O}_{2}\left(g\right)+{e}^{-}\to {{NO}_{2}}^{-}(ads)\stackrel{{\mathrm{NH}}_{4}^{+}(\mathrm{ads})}{\to }{NH}_{4}{NO}_{2}(\mathrm{ads})\to {N}_{2}\left(g\right)+{H}_{2}O\left(g\right)\). However, the bidentate nitrate and monodentate nitrate were also revealed on Fe-V-W/Ti, which combined with NH₄⁺ and decomposed into N₂ and H₂O, or N₂O and H₂O, respectively. The detected NH₂ species combined with NO on the Fe-V-W/Ti, following the E-R mechanism. As for VOCs, the intermediates of benzene and toluene were revealed by in situ DRIFTS study, and detailed Mars–van Krevelen mechanism was discovered.