Study on Performance and mechanism of low-temperature NH3-SCR denitrification over Mn/(Ce, La)PO4 catalysts

Abstract

Mn/(Ce, La)PO4 was synthesized by hydrothermal method, and NH3-SCR low-temperature denitration catalyst was prepared by changing Mn loading amounts. A series of characterization methods, such as XRD, BET, NH3-TPD, H2-TPR, etc., were used to investigate the effects of different loading amounts on the surface structure, chemical properties and denitrification activity of the catalysts, and the reaction pathways and denitrification mechanism were investigated by Fourier in-situ infrared detection. The results showed that the denitrification rate of the catalysts loaded with 5 % KMnO4 increased from 7.5 % to 83.8 % at 100 °C, and the optimal denitrification temperature was 250 °C, which was 50 °C lower than that of the unloaded catalysts, and the denitrification rate was 97.3 %. The introduction of Mn resulted in the appearance of a large number of amorphous manganese oxides appear on the surface of the catalysts, which promoted the dispersion of the active species Ce7O12. The increase of Brønsted acidic sites on the catalysts surface, the adsorption capacity of NH3 was significantly enhanced, the redox peak area increased, and the acidic sites increased, thus improving the denitrification activity at low temperature. The infrared results showed that the 5 %Mn/(Ce, La)PO4 sample is rich in Brønsted acid sites and strong in Lewis acid sites at the optimal activity temperature of 250 °C, which enhances the adsorption capacity of the catalysts for NH3. After the passage of the NO+O2 reaction, a large number of nitrate species were present on the surface of catalysts, while a large number of NO2 species were adsorbed, and these species promoted the NH3-SCR reaction on the surface of catalyst. The reactive species of the E-R mechanism are NH4+ species, NH3 species and gaseous NO, and the main reactive species of the l-H mechanism are NH4+ species adsorbed by Brønsted acid site, monodentate nitrate species and bidentate nitrate species.