Bimetallic bonding and mixed oxide formation in the Ga–Pd–CeO₂ system

The interaction of gallium and palladium with 2 nm CeO₂(111) layers grown on Cu(111) was studied by core level photoelectron spectroscopy and resonant valence band spectroscopy. Palladium alone interacted weakly with ceria layers. Gallium deposited on cerium dioxide formed a mixed Ga₂O₃–Ce₂O₃ oxide of 1:1 stoichiometry (cerium gallate CeGaO₃), with both metals in the M³⁺ oxidation state. Increasing Ga coverages led to the formation of lower oxidation states, i.e., Ga¹⁺ in Ga₂O oxide and metallic Ga⁰. Palladium deposited onto this complex system interacted with gallium leading to a breakage of Ga–ceria bonds, a decrease of the oxidation state of gallium, and formation of a Ga–Pd intermetallic alloy in which all components (CeO₂, CeGaO₃, Ga₂O, Ga–Pd, and Pd) are in equilibrium.