Oscillatory Strong Metal-Support Interaction in Pd/TiO₂ Under Redox Conditions

Strong metal-support interaction (SMSI) plays a crucial role in catalysis, with its encapsulation configuration being highly dependent on the chemical environments. However, the dynamic behavior of SMSI under redox conditions remains insufficiently understood. Here, environmental transmission electron microscopy (ETEM) revealed that SMSI overlayers form stably on the surface of Pd/TiO₂ nanocatalysts under pure O₂ and pure H₂ conditions, and exhibit oscillatory behavior under a redox condition with a 5:1 O₂/H₂ ratio at 0.05 Pa. Specifically, the outer layer of the SMSI overlayer, characterized primarily by typical oxidative SMSI, undergoes oscillations between formation and retraction near the Pd-TiO₂ interface. The SMSI oscillations locally modify the morphology of the TiO₂ support, with the SMSI overlayer serving as a temporary reservoir for Ti species to drive the tip growth of the support protrusion. Our work expands the understanding of the dynamic behavior of SMSI under reaction conditions and provides new insights into the solid-state growth mechanism.