Low-temperature NOx selective catalytic reduction activity evaluation of hollow-spherical manganese oxides

A novel tactic was employed to evaluate the low-temperature NH 3 -SCR (selective catalytic reduction) NO x removal property of manganese oxides (MnO x ) in various valence states, avoiding the influences of size, morphology and synthetic method on catalytic activity. Firstly, similar sized hollow-spherical MnO 2 , Mn 2 O 3 , Mn 3 O 4 and MnO were obtained by decomposing MnCO 3 at 440 and 500 °C in Air, 430 °C in H 2 and Ar, respectively. The orders of MnO x catalytic activity varied at different reaction temperature range, while MnO 2 showed the best NO conversion. Surface acidity has significant influences on the SCR activity, Mn 3 O 4 exhibits a better catalytic property than Mn 2 O 3 below 300 °C, and conversely, Mn 2 O 3 has a better high-temperature NO conversation than Mn 3 O 4 due to a stronger NH 3 adsorption ability above 300 °C. MnO will be oxidized in the studied atmosphere with 5% O 2 to Mn 3 O 4 , Mn 5 O 8 and finally to Mn 2 O 3 successively, and the mixed phases of MnO/Mn 3 O 4 or Mn 3 O 4 /Mn 5 O 8 exhibit a better catalytic activity than Mn 2 O 3 at 200–300 °C.