Effect of post-treatment on the selective catalytic reduction of NO with NH3 over Mn3O4

Abstract

The Mn3O4 nanocrystals were successfully prepared by rapid precipitation method at room temperature from MnSO4, H2SO4 and NH3•H2O, and the influences of post‒treatment temperatures at 200‒500 °C on texture, morphology, crystal face, redox and the selective catalytic reduction of NO with NH3 were investigated. The results show that a single tetragonal phase of Mn3O4 nanocrystals is obtained after dryness and it has a BET surface area of 112 m2/g and exposes the (101) plane. When the post‒treatment temperature increases from 200 to 400 °C, both crystal phase and crystallite sizes of Mn3O4 are almost unchanged, but their main exposed crystal faces change from (101) to (200) and (112). When the post‒treatment temperature increases to 500 °C, Mn2O3 is dissociated from Mn3O4. Mn3O4_300 possesses a developed pore structure with a SBET of 201 m2/g and a pore volume of 0.41 cm3/g. Mn3O4_400 has low reduction peaks at 210 and 467 °C and similar reduction properties after multi‒reaction of NH3‒SCR, but the peak temperature shifts to higher temperature compared to the fresh sample. When the post‒treated sample is applied to the NH3‒SCR reaction, Mn3O4_400 exhibits excellent NO removal efficiency at low temperatures, which may be related to the surface oxidation of Mn3O4 to promote the formation of NO2. Mn3O4_400 has good resistance of SO2 and has 92% removal efficiency of NO when only SO2 is induced in the simulated gas, but NO removal efficiency decreases to 63% in the presence of H2O and SO2 due to the generation of MnSO4•H2O.