Deactivation and regeneration of a commercial SCR catalyst: Comparison with alkali metals and arsenic

Deactivation of alkali metals and arsenic and regeneration methods are studied on commercial V₂O₅-WO₃/TiO₂ for the SCR reaction using experiments and DFT calculations. The poisoning of alkali metals is found to decrease the amount of Brønsted acid sites and the reducibility of active V⁵⁺ sites. Arsenic decreases the amount of Lewis acid sites and the stability of Brønsted acid sites and increases N₂O formation. After the catalysts are poisoned by both alkali metals and arsenic, the activity and N₂ selectivity are significantly suppressed. Diluted H₂SO₄ effectively removes alkali metals from the poisoned catalysts. Half of the amount of arsenic can be removed using a 4% H₂O₂ solution; however, some V₂O₅ and surface sulfates are also eliminated from the catalysts. The activity of the regenerated catalysts is almost recovered at high temperatures. From the DFT results on the V₂O₅/TiO₂ (001) plane, potassium and arsenic significantly alter the electronic structures of the V orbitals and broaden the band gap of the models. Interactions between potassium and arsenic are also found. Potassium covers the active sites of the models that are constructed by V₂O₅ and As₂O₅, which further decreases the number of acid sites. Potassium causes V and As orbitals to move to lower energies and inhibits the reactivity of the model.