Structure and redox properties of bulk and supported manganese oxide catalysts

The effects of the oxide carrier (gamma -Al2O3, SiO2, ZrO2, TiO2), MnOx precursor (KMnO4, Mn(NO3)(2) and Mn(CH3COO)(2)), loading (2-17 wt.% Mn) and preparation method on the structure and reduction pattern of MnOx-based catalysts have been systematically evaluated by X-ray diffraction (XRD) and temperature programmed reduction (TPR) measurements in the range 273-1073 K. Oxide precursor and preparation method determine both the structure and average oxidation number (A.O.N.) of the MnOx (1.5 <x <2) phase in bulk and supported systems. The reducibility scale, based on the inverse sequence of the onset temperature of reduction (T-o,T-red), MnO2/ZrO2 > MnO2/Al2O3 approximate to MnO2/TiO2 > MnO2/SiO2 similar or equal to MnO2 > Mn2O3, signals that the reduction pattern of MnOx catalysts depends upon Mn loading and nature of the oxide-support interaction, which control both dispersion and A.O.N. of the active phase.