Abstract: A manganese and cerium oxide catalyst was prepared through sol-gel method. Effects of the concentration and type of alkali metals on performance of the Mn-Ce/TiO₂ catalysts were investigated in selective catalytic reduction of NO with NH₃. The cause of the alkali metal poisoning of the catalyst was studied and the influence of sodium salt deposition on the activity retention fraction under different reaction conditions was further studied. The catalysts were characterized by scanning electron microscope (SEM), BET surface area, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), respectively. The results show that alkali metals exhibited an inhibiting effect on the selective catalytic reduction (SCR), and the deactivation rate of Mn-Ce/TiO₂ catalyst caused by potassium poisoning was higher than that by sodium poisoning. The NO conversion was decreased from 91.2% to 62.0% at a temperature of 160℃, when the potassium content was 2%. This is mainly because the presence of the alkali metal resulted in a reduction of the specific surface area of the catalyst, and the specific surface area of the potassium poisoning of the catalyst was reduced by 34.2%. The alkali metal poisoning could cause blockage of the micropores on the surface and the transfer from anatase to rutile phase of the catalyst. The effect of alkali metal on the retention fraction of the Mn-Ce/TiO₂ catalyst indicates that the particle size of the catalyst had slight effect on its activity retention fraction. The selective catalytic reduction (SCR) activity of the Mn-Ce/TiO₂ catalyst increased along with the temperature. While the content of alkali metal decreased, the retention rate of active metal increased. The inhibitory effect of Na₂SO₄ and NaCl on the denitrification activity of Mn-Ce/TiO₂ catalyst was more significant than that of NaNO₃.