Atmosphere-Dependent Encapsulation and Dewetting in Au/ZnO: A Transient-Overlayer Strategy for Maximizing Metal-Support Interfacial Catalysis

The strong metal-support interaction (SMSI) has traditionally been viewed as a static phenomenon that modulates catalysis through site blocking. Here, we challenge this classical view by demonstrating that SMSI in Au/ZnO is an atmosphere-dependent dynamic process that can be harnessed to engineer catalytic interfaces. Using in situ transmission electron microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy, we track the structural evolution of the Au/ZnO interface throughout redox cycles and reaction conditions. Under H₂, oxygen vacancy formation triggers ZnO_x encapsulation, followed by AuZn alloying at elevated temperature, which induces nanoparticle reconstruction and expands the metal-support interfacial area. Upon exposure to O₂, the alloy decomposes, and the ZnO_x overlayer dewets into nanoislands, with some regions undergoing complete retraction. Under CO oxidation conditions, the fully encapsulated state is lost, yet the H₂-pretreated catalyst exhibits superior activity and stability. This enhancement arises from alloying-induced interface reconstruction together with residual ZnO nanoislands that persist after dewetting, creating an enlarged and highly active metal-oxide interface. Our work demonstrates a transient-overlayer strategy for catalyst design, in which a pre-formed SMSI layer serves as a precursor that, through controlled redox cycling or reaction conditions, transforms into a high-interface area, sintering-resistant catalytic architecture, thereby transcending the classical encapsulation-activity dilemma.