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

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.