Formation of Pd-Ce intermetallic compounds by reductive metal-support interaction

The intermetallic compound (IC) formation between Pd and Ce via reductive metal-support interaction (RMSI) has been studied using two different Pd/CeO2 materials: A thin film of Pd particles embedded in fluorite-type CeO2, grown on vacuum-cleaved NaCl(001) facets and CeO2 powder impregnated with small Pd particles. The reduction of CeO2 and formation of different Pd-Ce intermetallic compounds has been monitored by diffraction in an electron microscope and synchrotron-based in situ X-ray diffraction, and is complemented by density functional theoretical calculations (DFT) of the formation enthalpies to judge the relative stabilities of the formed intermetallic compounds. On both studied materials, the formation of similar ICs, namely CePd3 and CePd5, has been observed for the first time at temperatures of 1100 K following RMSI and, thus, indicates that any catalytic pre-treatment in hydrogen, provided the reduction temperature is high enough, must also be considered for the Pd-CeO2 system. The studies are complemented by a brief review of the Pd-Ce phase diagram to discuss the potential pathways of Pd-Ce intermetallic compound formation.