Effect of MnO2 crystal types on CeO2@MnO2 oxides catalysts for low-temperature NH3-SCR

A series of MnO2 (with different crystal types) doping CeO2 catalysts were synthesized by combining hydrothermal method and impregnation method, and the SCR activity and N2O formation of the catalysts were investigated. The results showed that NO conversion rate of CeO2 @ α-MnO2, CeO2 @ β-MnO2 and CeO2 @ γ-MnO2 catalysts from 75 to 250 °C was always more than 95%, which showed excellent low-temperature NH3-SCR activity. N2O amount produced by CeO2 @ α-MnO2, CeO2 @ β-MnO2 and CeO2 @ γ-MnO2 catalysts during denitrification all reduced at 75–125 °C comparing with pure MnO2, and the N2O in denitration process mainly came from SCR reaction, but not from direct oxidation of NH3. Besides, the reducibility and acidity of the complex oxides catalyst were improved, which was more beneficial to the reaction of adsorbed NH3 with NO, thus reducing the direct oxidation of adsorbed NH3 by O2 and inhibiting the formation of N2O. What’s more, the effect of Ce and different crystal types of MnO2 also influenced N2O generation behavior. Moreover, the SCR reaction of CeO2 @ α-MnO2 and CeO2 @ β-MnO2 catalysts mainly followed Eley-Rideal (E-R) mechanism, while CeO2 @ γ-MnO2 catalyst followed Langmuir-Hinshelwood (L-H) mechanism.