Density Functional Calculations of the Sequential Adsorption of Hydrogen on Single Atom and Small Clusters of Pd and Pt Supported on Au(111)

We have used density functional theory calculations to study the sequential adsorption of hydrogen on Pd and Pt atomic site catalysts such as single-atom alloy catalysts (SAAC), single-atom catalysts (SAC), and single cluster catalysts (SCC) on Au(111). The results show that Pd systems tend to have near-zero free energy of hydrogen adsorption ( $$\Delta {G}_{{\mathrm{H}}_{\mathrm{ads}}}\approx 0$$ ) under various coverage conditions of adsorbed hydrogen. In the case of Pt systems, $$\Delta {G}_{{\mathrm{H}}_{\mathrm{ads}}}\approx 0$$ only at high coverage conditions of adsorbed hydrogen. Such differences come from the preference of hydrogen for high-coordination and low-coordination sites on Pd and Pt, respectively. The low coordination of hydrogen results in multiple adsorption sites with $$\Delta {G}_{{\mathrm{H}}_{\mathrm{ads}}}\approx 0$$ in SCC of Pt/Au. These results can help to understand the different catalytic properties of Pd/Au and Pt/Au.