Revealing the Impact of Metal–Support Interactions on the Surface Structure of Ceria-Supported Pd–Cu Bimetallic Model Catalysts

Metal–support interactions (MSIs) play a decisive role in determining the surface structure, electronic properties, and catalytic behavior of oxide-supported bimetallic catalysts, yet their influence at the atomic scale remains insufficiently understood. Here, we investigate the impact of MSIs on the structural evolution of ceria-supported Pd–Cu bimetallic model catalysts prepared with controlled deposition sequences under ultrahigh vacuum conditions. Using well-defined Pd/Cu/CeO2(111) and Cu/Pd/CeO2(111) systems, we systematically elucidate how the order of metal deposition governs alloy formation, surface segregation, and interfacial chemistry. Synchrotron radiation photoemission spectroscopy, high-resolution X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and temperature-programmed desorption reveal that Cu deposition onto Pd-precovered CeO2 induces strong Cu–CeO2 interactions, driving Cu diffusion to the metal–oxide interface and displacing Pd to form an extended Cu–Pd alloy. In contrast, Pd deposition onto Cu-precovered CeO2 results in limited interdiffusion, yielding a Cu@Pd core–shell structure due to the weaker Pd–CeO2 interaction. Modulating the ceria oxidation state further confirms that alloy formation is governed by interfacial dynamics controlled by MSIs. These structural differences directly influence hydrogen adsorption and spillover behavior, with Cu-induced dilution of Pd–Pd coordination enhancing hydrogen spillover from Pd to Cu sites. This work provides fundamental insights into MSI-regulated bimetallic surface structures and establishes a rational framework for designing oxide-supported Pd–Cu catalysts with tailored active phases for selective hydrogenation reactions.