Synthesis and Dynamics of Stable, Highly-Dispersed Precious Metal Model Catalysts

Surface science studies provide a unique platform for studies of atomically precise materials, focusing on their structure, stability, and activity. These well-defined systems, often homotopic, are essential for validating theoretical methods and uncovering structure-activity relationships in more complex catalytic environments. The studies presented here demonstrate approaches for stabilizing highly dispersed late transition metals, both as single atoms and nanoclusters. High-resolution imaging, spectroscopic characterization, reactivity measurements, and density functional calculations were employed to gain mechanistic insights into their structure, thermally induced evolution, and activation in chemical environments. Specifically, the temperature and coverage-dependent formation and stability of monodispersed PdTe_x nanoclusters on WTe₂(001) and mixed Rh-Fe₃O₄(001) surfaces will be discussed. On WTe₂(001), Pd clusters are shown to not interact with surface defects but rather react with intercalated Te. Upon annealing, stable monodispersed PdTe_x clusters form due to registry with the underlying WTe₂(001). For Rh-Fe₃O₄(001) system, the stability of undercoordinated Rh adatoms is compared with that of Rh atoms embedded in the surface layer. Further, formic acid is used to probe the activity of such single Rh atoms. Formate and hydroxyl intermediates are shown to destabilize in-surface Rh, transiently converting it to highly active Rh adatoms that revert back to in-surface Rh when the reaction cycle is complete. These studies provide mechanistic insight into model catalytic systems, which is essential for understanding complex high-surface-area catalysts.