The promotional effects of cerium on the catalytic properties of Al2O3-supported MnFeOx for NO oxidation and fast SCR reaction

Abstract

To reveal the cooperative effects of cerium with manganese and iron on the catalytic oxidation of NO to NO2 and the catalytic activity in the fast selective catalytic reduction (SCR) reaction, Ce–MnFeOx/Al2O3 catalysts were prepared with different amounts of cerium doping. The results showed that the oxidation rate of NO to NO2 achieved by MnFeOx/Al2O3 was obviously improved with cerium doping. The highest catalytic activity, corresponding to NOx conversion >95.5% within the range of 100–350 °C and NO oxidation rate of 55.1% at 350 °C, was obtained when using Ce1.0–MnFeOx/Al2O3 (Ce:Fe:Mn = 1:2:16), Furthermore, according to characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), H2-temperature-programmed reduction (TPR), NH3-temperature-programmed desorption (TPD), NO-TPD, and X-ray photoelectron spectroscopy (XPS) techniques, the active element dispersion and combination of iron and manganese were both enhanced with cerium doping, while the metal oxide crystallinity was reduced. Cerium doping improved the Mn4+/(Mn2+ + Mn3+ + Mn4+) and Fe3+/(Fe2+ + Fe3+) ratios, while increasing the amounts of lattice oxygen and oxygen vacancies, thereby promoting the oxidation rate of NO to NO2 and ultimately facilitating the fast SCR reaction. However, excess cerium doping led to crystallization of ceria. This study revealed that Ce1.0–MnFeOx/Al2O3 has potential for application as an excellent catalyst with efficient catalytic activity in NO preoxidation and the fast SCR reaction.