The poisoning of alkali metal on MnOx/TiO2 catalysts used for selective catalytic reduction (SCR) of NO by NH3 was investigated. KNO3, KCl and K2SO4 were doped on MnOx/TiO2 catalysts by sal-gel method, respectively. The SCR activity of each catalyst was measured for the removal of NOx with NH3 in the temperature range 90-330 degrees C. The experimental results showed that catalyst with KNO3 have a stronger deactivation effect than other catalysts. The properties of the catalysts were characterized by XRD, BET, SEM, XPS, H-2-TPR, NH3-TPD and in situ DRIFTS analyses. The characterized results indicated that KNO3, KCl and K2SO4 caused the similar decrease of specific surface area and pore volume, but the quantity of acid sites for KNO3-MnOx/TiO2 catalyst reduced sharply. The main reason for catalyst deactivation is attributed to two aspects: one was physical influences for the decrease of surface area and pore volume, another was chemical influences that the K+ ions decomposed by KNO3 neutralized Bronsted acid sites of catalyst and reduced their reducibility. The chemical influence played a leading role on the deactivation of catalysts. (C) 2015 Elsevier B.V. All rights reserved.