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.