Characterization of manganese and iron oxides as combustion catalysts for propane and propene

Mn2O3-Fe2O3 powders have been prepared by a coprecipitation method. The pure compounds have been characterized as constituted of alpha-Fe2O3 (haematite) and alpha-Mn2O3 (bixbyite) while the mixed oxides are constituted of a mixture of haematite- and bixbyite-structure solid solutions. The observed reciprocal solubilities calculated from the XRD patterns approach the thermodynamic ones. alpha-Mn2O3 is more active than alpha-Fe2O3 as catalyst for both propane and propene oxidation. However, alpha-Mn2O3 is less active than Mn3O4 powder. Propene oxidation is in all cases very selective to CO2 while propane oxidation gives rise to significant amounts of propene on alpha-Fe2O3. Mn2O3-Fe2O3 powders are slightly more active than alpha-Mn2O3 as combustion catalysts. The selectivities to propene upon propane oxidation decrease with increasing Mn content. (C) 1998 Elsevier Science B.V. All rights reserved.