Effect of preparation methods on selective catalytic reduction of NO_x with NH₃ over manganese oxide octahedral molecular sieves

A series of manganese oxide octahedral molecular sieves (OMS-2) were prepared by different methods for the purpose of investigating the effect of the preparation methods on their catalytic properties in selective catalytic reduction (SCR) of NO_x with NH₃. These samples were characterized with BET, XRD, Raman, H₂-TPR, XPS and TEM techniques. It was found that all the samples showed higher NO_x conversions than MnO_x in the temperature range from 50 to 150 ℃ due to their easier reduction behavior, and the NO_x conversion reached about 100% at 120 ℃. Nonetheless, the preparation methods have a great effect on the catalytic activity of OMS-2. The sample prepared by the solid-state method shows the highest catalytic activity. The BET, XRD, TEM and XPS results reveal that this because it has lower crystallinity but higher dispersion as result of the presence of larger amounts of surface lattice oxygen and less crystalline MnO₂ species.