Substitution of WO3 in V2O5/WO3–TiO2 by Fe2O3 for selective catalytic reduction of NO with NH3

Abstract

To improve N₂ selectivity and lower the cost, WO₃ in V₂O₅/WO₃–TiO₂ was substituted by a low cost composition Fe₂O₃ for selective catalytic reduction (SCR) of NO with NH₃. The SCR reaction over V₂O₅/Fe₂O₃–TiO₂ mainly followed the Eley–Rideal mechanism (i.e. the reaction between activated ammonia species and gaseous NO). There were two active components on V₂O₅/WO₃–TiO₂ for the activation of adsorbed NH₃ (i.e. V⁵⁺ and Fe³⁺). The acid sites on V₂O₅/Fe₂O₃–TiO₂ mainly resulted from the support Fe₂O₃–TiO₂, so the adsorbed NH₃ preferred to be activated by Fe³⁺ rather than by V⁵⁺. V⁵⁺ on V₂O₅/Fe₂O₃–TiO₂ could accelerate the regeneration of Fe³⁺ on Fe₂O₃–TiO₂ due to the rapid electron transfer between V⁵⁺ and Fe²⁺ on the surface, so the activation of adsorbed NH₃ by Fe³⁺ was promoted. As some NH₃ adsorbed on V₂O₅/Fe₂O₃–TiO₂ was not activated by Fe³⁺, the inactivated NH₃ could then be activated by V⁵⁺ on the surface. As a result, 2% V₂O₅/Fe₂O₃–TiO₂ showed excellent SCR activity, N₂ selectivity and H₂O/SO₂ durability at 300–450 °C. Furthermore, the emission of 2% V₂O₅/Fe₂O₃–TiO₂ to the fly ash can be prevented by an external magnetic field due to its inherent magnetization. Therefore, 2% V₂O₅/Fe₂O₃–TiO₂ could be a promising low-cost catalyst in NO emission control.