Characterization and hydrocarbon oxidation activity of coprecipitated mixed oxides Mn3O4/Al2O3

The surface and redox properties of the manganese oxides Mn3O4 (hausmannite), Mn2O3 (bixbyite) and MnO2 (pyrolusite) and of coprecipitated manganese aluminum Mn3O4/Al2O3 mixed oxide catalysts have been investigated by FT-IR spectroscopy of adsorbed probe molecules methanol and pyridine. Methoxy groups interacting with Mn3+, Mn2+ and Al3+ cations are well distinguishable with respect to the position of their C-O stretching band. The evolution of methoxy groups to formate species allows to obtain information on the reducibility of the surfaces. Also pyridine allows to distinguish such sites and to evaluate their surface acidity. The results concerning the catalytic oxidation of propane over these materials are discussed in relation to their surface properties. The effect of bulk oxygen diffusion rate on the catalytic oxidation rate is evident. (C) 2001 Elsevier Science B.V. All rights reserved.