Structural effects of iron spinel oxides doped with Mn, Co, Ni and Zn on selective catalytic reduction of NO with NH3

The iron spinel oxides doped with Mn, Co, Ni and Zn were studied for selective catalytic reduction (SCR) of NO with NH3. From the TPR and TPD results, the redox properties and surface acidity of metal-doped iron oxides are determined by the structural effects of iron spinet oxides. At high temperatures, it was found that the NH3-related reaction follows the Lewis-acid-inspired E-R mechanism, which involves in the competition between NH3 catalytic reduction with NO (NH3-CR) and NH3 catalytic oxidation to NOx (NH3-CO). The doping of Co, Ni or Zn into iron spinel structures inhibits the redox cycle of Fe3+/Fe2+ between gamma-Fe2O3 and Fe3O4 on the surface octahedral sites, resulting in the decrease of NH3 activation and NH3-SCR performance. However, the maghemite-type spinel structure was maintained and the outermost surface coverage of Mn was enhanced after the doping of Mn. Thus, Mn-doped spinel oxide exhibits high NH3-SCR activity but poor N-2 selectivity at low temperatures. (C) 2013 Elsevier B.V. All rights reserved.