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 Bronsted acid sites and the reducibility of active V5+ sites. Arsenic decreases the amount of Lewis acid sites and the stability of Bronsted acid sites and increases N2O formation. After the catalysts are poisoned by both alkali metals and arsenic, the activity and N-2 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. (C) 2014 Elsevier B.V. All rights reserved.