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<p>Single-atom alloys can be effective catalysts and have been compared to supported
single-atom catalysts. To rationally design single-atom alloys and other surfaces with localized
ensembles, it is crucial to understand variations in reactivity when varying the dopant and the
ensemble size. Here, we examined hydrogen adsorption on surfaces embedded with localized
clusters and discovered general trends. Counterintuitively, increasing the amount of a more
reactive metal sometimes makes a surface site less reactive. This behavior is due to the localized
electronic states in many of these surfaces, making them similar to free-standing nanoclusters.
Further, single-atom alloys have qualitatively different behavior than larger ensembles.
Specifically, the adsorption energy is U-shaped when plotted against the dopant’s group for
single atom alloys. Additionally, adsorption energies on single atom alloys correlate more
strongly with the dopant’s p-band center than the d-band center.
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