Key Takeaways & Executive Findings
- •• • 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.
Abstract
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.
1. Introduction
CO adsorption on Pt-based catalysts is central to many industrial processes, including CO oxidation, water-gas shift, and methanol synthesis. However, the strong adsorption of CO often leads to catalyst poisoning, particularly on Pt surfaces, which severely limits catalytic efficiency and longevity. Traditional approaches to mitigate poisoning, such as alloying or using oxide supports, have achieved only partial success, as they often compromise activity or selectivity. The fundamental challenge lies in understanding and controlling the electronic interactions between CO and Pt at the atomic level, which dictate adsorption strength and subsequent reactivity.
This study addresses this bottleneck by systematically investigating the effect of Pt cluster size on CO adsorption using DFT calculations combined with spectroscopic and charge analysis. By comparing Pt4 and Pt13 sub-nanometric clusters supported on γ-Al2O3, the authors elucidate how cluster size modulates d-electron back-donation, thereby controlling the C–O bond strength and vibrational frequency. The findings provide a clear correlation between Pt dispersion, electronic structure, and adsorption properties, offering a rational basis for designing catalysts with optimized CO adsorption strength—balancing high activity with resistance to poisoning. This atomic-scale insight is crucial for advancing catalyst design in CO-related reactions.
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HE Kai, SU Xuyan, QU Zhuang, YANG Ye, QIN Yucai, SONG Lijuan (2026). Mechanistic Insights into CO Adsorption Modes on Pt-Based Supported Catalysts. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60643-3
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Frequently Asked Questions
How does the Pt cluster size affect the d-electron back-donation and consequently the CO adsorption strength?
Small Pt4 clusters, with highly unsaturated Pt atoms, exhibit strong d-electron back-donation, leading to increased electron transfer into CO π* orbitals (e.g., +0.18 e for multi-terminal and +0.22 e for bridge adsorption). This weakens the C–O bond, causing a redshift in IR frequency. In contrast, large Pt13 clusters have a dense structure that promotes electron delocalization, reducing surface electron density and back-donation, resulting in a blueshift and stronger C–O bond.
What is the industrial significance of the 81 cm−1 IR blueshift observed for bridge adsorption from Pt4 to Pt13?
The 81 cm−1 shift indicates a substantial change in CO adsorption strength with Pt cluster size. This sensitivity implies that precise control of Pt dispersion can tune the adsorption energy, which is critical for optimizing catalytic activity and selectivity. For industrial applications, this means that by adjusting Pt loading or preparation methods, one can design catalysts with desired CO binding strengths to balance activity and resistance to poisoning.
Can the 'saturation effect' in multi-terminal adsorption be exploited to maintain consistent catalytic performance across different Pt loadings?
Yes, the stability of IR frequency for multi-terminal adsorption suggests that this mode is less affected by Pt cluster size. This could be advantageous for maintaining uniform catalytic behavior in reactors where Pt dispersion may vary. However, the overall catalytic performance also depends on the relative abundance of different adsorption modes, which may change with cluster size.
How do the DFT results correlate with experimental FT-IR data, and what are the limitations of this computational approach?
The DFT calculations are complemented by FT-IR spectroscopy, and the observed trends in vibrational frequencies align with the theoretical predictions. However, DFT models idealize the catalyst surface and may not fully capture the complexity of real supported catalysts, such as support effects, defects, or dynamic restructuring under reaction conditions. Nevertheless, the qualitative agreement provides confidence in the mechanistic insights.
What are the practical implications of this study for designing Pt-based catalysts with enhanced resistance to CO poisoning?
The study suggests that by increasing Pt cluster size (e.g., from Pt4 to Pt13), the back-donation is weakened, reducing CO adsorption strength and potentially mitigating poisoning. However, this may also lower catalytic activity for CO-involved reactions. Therefore, a trade-off exists, and optimal performance may require a balance, possibly achieved by tuning cluster size or using promoters to modify electronic properties.
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