Ultrathin Oxide Films for Heterogeneous Catalysis: Structure, Defects, and Reactivity

Ultrathin oxide films on metal substrates have emerged as powerful model systems for heterogeneous catalysis, enabling direct correlation of atomic-scale structure with reactivity. Beyond serving as support for metal clusters, these films exhibit intrinsic catalytic activity, governed by film thickness, lattice mismatch, defect landscape, and the oxide-metal interfacial coupling, properties that often have no direct counterpart in bulk oxides. Separating these effects requires an atomistic characterization of structure, composition, and defect populations under increasingly realistic conditions. In this review, we survey the structural and electronic features of ultrathin oxide films, with particular emphasis on point defects, extended defects, and interfacial charge transfer, and connect each to representative catalytic behavior. Given the scope of this review, we limit our discussion to 3d transition metal oxides, wide band gap oxides, and charge transfer insulator type main group oxides. Finally, we outline the remaining experimental challenges and highlight emerging operando, time-resolved, and tip-enhanced techniques that deliver the spatial and chemical resolution needed to probe oxide surfaces under reaction-relevant conditions.