A Study of Cerium–Manganese Mixed Oxides for Oxidation Catalysis

Cerium–manganese mixed oxides with compositions of Ce0.5Mn0.5O1.75 and Ce0.8Mn0.2O1.9 were prepared by the citric-acid (Pechini) method and their catalytic properties were compared to CeO2 and Mn2O3. The mixed oxides exhibited higher specific rates than either CeO2 or Mn2O3 for oxidation of both methane and n-butane. While XRD measurements of the mixed oxides suggested that the materials had primarily the fluorite structure, oxygen isotherms, measured by coulometric titration at 973 K, exhibited steps associated with MnO–Mn3O4 and Mn3O4–Mn2O3 equilibria, implying that manganese oxide must exist as separate phases in the solids. The P(O2) for the MnO–Mn3O4 equilibrium is shifted to lower values in the mixed oxides, indicating that the manganese-oxide phase is affected by interactions with ceria.