Molybdenum-decorated V2O5–WO3/TiO2: surface engineering toward boosting the acid cycle and redox cycle of NH3-SCR

Abstract

The accelerated acid cycle corresponding to NH₃ activation and redox cycle that requires electron transfer between V⁴⁺ and V⁵⁺ are regarded the two essential factors determining low-temperature ammonia selective catalytic reduction (NH₃-SCR). In this work, highly dispersed submonolayer Mo-decorated V₂O₅–WO₃/TiO₂ catalysts were developed for efficient NO_x abatement at low temperature (<300 °C). The 7 wt% MoO₃-decorated V₂O₅–WO₃/TiO₂ (7Mo–VW/Ti) catalyst presented outstanding NH₃-SCR performance at 230–400 °C and displayed a high tolerance to SO₂ and H₂O. Compared with V₂O₅–WO₃/TiO₂, more active dimeric and polymeric vanadia species existed in the submonolayer 7Mo–VW/Ti catalyst, which were more reactive with NH₃ at terminal VO sites in the polynuclear structure. More Brønsted acid sites were formed due to the enrichment of polynuclear vanadia species and MoO₃, which favors NH₃ adsorption, thus speeding up the acid cycle. Additionally, the increased number of V⁴⁺ species produced by the MoO₃ additive enhanced the redox properties, accelerating the process of the V⁵⁺/V⁴⁺ redox cycle. Therefore, the surface engineering of V₂O₅–WO₃/TiO₂ by MoO₃ enhanced the acid and redox cycling of NH₃-SCR. Furthermore, adsorbed NH₃ species, especially when adsorbed on Brønsted acid sites, primarily reacted with gaseous NO and subsequently yielded N₂ and H₂O, following the Eley–Rideal mechanism.