Adsorption of CO oxidation intermediates on Ag Au nanoparticles across quantum-confined to bulk-like size regimes

Density functional theory calculations were used to quantify and explain the characteristics of CO and atomic O adsorption on monometallic and bimetallic Ag Au cuboctahedral nanoparticles consisting of 13, 55, 147, and 309 atoms. An analysis of the associated density of states reveals that 55-atom sized nanoparticles mark the crossover from quantum-confined to bulk-like electronic behavior. At this transitional size, the adsorption energies of core-shell morphologies show pronounced deviation from their monometallic counterparts. Our investigation also reveals that adsorbate coverage influences energetics via competing effects: electronic d-band center shifts that weaken binding versus strain-driven relaxations that can strengthen it. Further examination of substitutional alloying of the metallic systems indicates that adjacent (same-layer) incorporation of the secondary metal affects adsorption more strongly than sublayer (subsurface) substitution. Accordingly, the greater deviations observed for core-shell structures can be attributed to stronger core-shell coupling rather than solely due to sublayer effects. Our findings highlight how local surface composition, electronic coupling, and corrected electronic descriptors can be used for the rational design of bimetallic catalysts.