Mn-Ce/AC catalysts for low-temperature NH3-SCR of NOx were deliberately loaded with various potassium salts (KCl, KNO3, and K2SO4) to investigate the influence of the counter-ions on the poisoning impact. Whereas K salts poisoning had only marginal impact on the textural properties of the catalysts, but it altered the chemical properties of the catalysts significantly. Potassium addition lowered the relative surface concentration of Mn4+ and M-O in Mn-Ce/AC catalyst, suggesting that K might occupy the oxygen vacancies around Mn atoms, thereby weakening the NH3 adsorption. The extent of inhibition strongly depended on the anion, with Cl- causing a higher degree of poisoning than that of either NO3- or SO42- . While K+ could hinder NH3 adsorption, both NO3and SO42- provided new acid sites that could offset the deactivation.