• • Pt4 clusters induce strong d-electron back-donation, with electron transfer values of +0.18 e (multi-terminal) and +0.22 e (bridge), leading to significant C–O bond weakening and IR redshift; this enhances CO activation for oxidation reactions but may increase poisoning risk.
• • Pt13 clusters exhibit weakened back-donation due to electron delocalization, resulting in reduced net electron gain by CO and a blueshift in IR frequency; this can improve CO tolerance but lower catalytic activity for CO-involved reactions.
• • Bridge adsorption is highly size-sensitive, showing an IR blueshift of 81 cm−1 from Pt4 to Pt13, indicating that precise control of Pt dispersion can tune CO adsorption strength and catalytic performance.
• • Multi-terminal adsorption exhibits frequency stability due to a 'saturation effect', suggesting that this adsorption mode is less affected by cluster size, which is crucial for consistent catalytic behavior across different Pt loadings.