Mechanistic Insights into CO Adsorption Modes on Pt-Based Supported Catalysts
The adsorption behavior and electron transfer mechanism of CO on Ptn/γ-Al2O3 catalysts (n = 4, 13) were systematically investigated using density functional theory (DFT) calculations, complemented by infrared (IR) spectroscopy, electron difference density (EDD), and charge decomposition analysis (CDA). The study reveals that Pt cluster size critically governs the adsorption configuration, electron transfer, and C–O vibrational frequency. For small Pt4 sub-nanometric clusters, highly unsaturated Pt atoms exhibit strong d-electron back-donation, leading to substantial filling of CO π* antibonding orbitals, significant weakening of the C–O bond, and a redshift in IR frequency. Conversely, large Pt13 clusters, characterized by dense structures and electron delocalization, exhibit weakened back-donation, enhanced C–O bonding, and a blueshift. The electron transfer intensity follows the order: linear < bridge < multi-terminal adsorption. Bridge adsorption is most sensitive to cluster size, displaying an IR blueshift of 81 cm−1 when Pt atoms increase from 4 to 13. Multi-terminal adsorption shows stable frequencies due to a 'saturation effect'. This study establishes a comprehensive correlation among Pt size, electronic structure, adsorption properties, and infrared response, providing atomic-scale theoretical guidance for designing efficient Pt-based catalysts with optimized CO adsorption strength and resistance to poisoning.