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 a luminum Mn3O4/Al2O3 mixed oxide catalysts have been investigated by FT-IR s pectroscopy of adsorbed probe molecules methanol and pyridine. Methoxy grou ps interacting with Mn3+, Mn2+ and Al3+ cations are well distinguishable wi th respect to the position of their C-O stretching band. The evolution of m ethoxy groups to formate species allows to obtain information on the reduci bility of the surfaces. Also pyridine allows to distinguish such sites and to evaluate their surface acidity. The results concerning the catalytic oxi dation of propane over these materials are discussed in relation to their s urface properties. The effect of bulk oxygen diffusion rate on the catalyti c oxidation rate is evident. (C) 2001 Elsevier Science B.V. All rights rese rved.