Alkali-driven active site shift of fast SCR with NH3 on V2O5–WO3/TiO2 catalyst via a novel Eley–Rideal mechanism

Abstract

The heterogeneous SCR reaction dynamics, the well-known Eley–Rideal mechanism and the Langmuir–Hinshelwood mechanism are well-understood by most researchers, all involving the adsorption of ammonia as the premise of the whole redox reaction. Alkali species prevent the collision between the acidic V-site and gaseous NH₃ molecules and result in serious reactivity losses to the commercial V₂O₅–WO₃/TiO₂ catalyst. Yet, in fast SCR reactions, alkali species provide additional basic sites for NO₂ adsorption. In contrast to the accepted mechanism, gaseous NH₃ molecules were shown to participate in the reaction and react with other adsorbed substances. The active site is transformed and the mechanism shifts to a fast SCR over the poisoned catalyst. This study presents a new strategy to design catalysts for fast SCR processes and deal with alkali metal poisoning issues.