Potassium poisoning impact on FeCu selective catalytic reduction catalyst: Structure and mechanism

•K causes damage to Cu-O-Fe construction.•The decrease of Cu-O-Fe species and increase of Cu-O-Cu species reduce acid sites.•The existence of CuO leads to excessive oxidation of NH3.•Only bidentate nitrates can generate and react with NH3 after K poisoning.•The reaction rate decreases distinctly after K poisoning.