Titania supported bimetallic transition metal oxides for low-temperature SCR of NO with NH3

High surface area titania supported Mn-Cu and Mn-Cr bimetallic oxides were prepared by wet impregnation method using their nitrate salts. The catalytic activity of these materials was evaluated for selective catalytic reduction (SCR) of NO with NH3 in the presence of excess oxygen at low temperatures (373-523 K). The surface and bulk properties of the catalysts were examined using X-ray diffraction, BET-surface area, FT-IR, temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) techniques. X-ray diffraction (XRD) studies revealed the formation of definite crystalline compounds MnCrO3 and CrMn1.5O4 for Mn-Cr/TiO2 samples and Cu1.4Mn1.6O4 and Cu1.5Mn1.5O4 for Mn-Cu/TiO2 samples. The specific surface areas of the prepared catalysts were significantly lower than the pure TiO2 support. The FT-IR studies indicate that the acidic strength of these catalysts was higher than the corresponding single oxide catalysts. TPR studies suggest that the shift in the reduction peak position toward higher temperatures in bimetallic oxides is probably due to the formation of binary or ternary metal oxide phases, as observed from XRD study. The XPS peak intensities and the corresponding binding energies indicate that the surface concentration of Mn is lower than either Cu or Cr at equal metal loadings. A slight shift of the Mn 2p XPS line toward higher binding energies (642.1 eV) was observed in the case of Mn-Cu/TiO2 and Mn-Cr/TiO2 catalysts. This is due to the formation of stoichiometric mixed oxide phases between promoted metal oxides, which was observed in the XRD study. The core level binding energy values indicate that the manganese is present as Mn(IV) in both the catalysts. The activity results of these catalysts were compared with their corresponding single oxide catalysts.