Thermodynamic Investigation of the Redox Properties of Ceria-Zirconia Solid Solutions

The thermodynamic properties of solid solutions of ceria and zirconia, having the general formula Ce1-y Zry O2, were studied as a function of temperature and oxygen fugacity by measuring the oxygen content of samples equilibrated in H2/H2O mixtures between 873 and 1173 K. The thermodynamic redox properties were found to be a strong function of oxide composition but were independent of sample surface area and calcination temperature. Ceria-zirconia solid solutions were much more easily reduced than CeO2, so that thermodynamic values such as the enthalpy of oxidation for ceria are not the same as for the solid solution. All of the reduction isotherms for the ceria-zirconia solutions exhibited a plateau in the oxygen stoichiometry at the higher oxygen fugacities accessible using H2/H2O mixtures, suggesting special stabilities for certain reduction states in the solid solutions.