A renewed interest of benchmark V2O5/WO3/TiO2 SCR-catalysts is discernible for the depollution of stationary sources jointly with the use of bio-fuels as substitute to fossil fuels. However, the resistance to deactivation has to be reconsidered according to additional alkaline contamination. This study tried to elucidate the impact of potassium on the stability of vanadate and tungstate species at various dispersions for two different K/V ratios equal to 0.2 and 0.8. Different kinetic behaviors of fresh and K-poisoned catalysts have been discussed based on the affinity of potassium to neutralize preferentially strong acid sites as well as to alter the capability of V=O redox sites.