Phase equilibria in the system Ce-Pd-O

Abstract

Despite its relevance to automotive exhaust catalysis, air purification and gas sensors, a phase diagram for the system Ce-Pd-O is not found in the literature. The phase diagrams of Ln-Pd-O (Ln = light lanthanide element) systems show three inter-oxide compounds (Ln4PdO7, Ln2PdO4, Ln2Pd2O5). Based on systematic trends in experimentally determined thermodynamic properties of these three ternary oxides, the Gibbs energy of formation of three cerium-palladium oxides (Ce4PdO7, Ce2PdO4, Ce2Pd2O5) are evaluated as a function of temperature.The estimated data for the three inter-oxide compounds along with evaluated data for the binary system Ce-Pd and data for binary oxides from the literature are used to compute the ternary phase diagram of the system Ce-Pd-O at 1100 K. All the three inter-oxide compounds are found to be unstable because of the enhanced stability of higher oxides of cerium compared to Ce2O3. An isothermal section of the phase diagram and an oxygen potential-composition diagram for the system Ce-Pd-O at 1100 K are computed from thermodynamic data.