Argon Adsorption on Cationic Gold Clusters Aun+ (n ≤ 20)

Adsorption of O2 on the Preferred -O-Au Sites of Small Gold Oxide Clusters: Charge-dependent Interaction and Activation

Decades of research have illuminated the significant roles of gold/gold oxide clusters in small molecule catalytic oxidation. However, many fundamental questions, such as the actual sites to adsorb and activate O2 and the impact of charge, remain unanswered. Here, we have utilized an improved genetic algorithm program coupled with the DFT method to systematically search for the structures of Au1-5Ox-/+/0 (x = 1-4) and calculated binding interactions between Au1-5Ox-/+/0 (x = 1-2) and O2, aiming to determine the active sites and to elucidate the impact of different charge states in gold oxide systems. The results revealed that the reactivity of all three kinds of small gold oxide clusters toward O2 is strongly site-dependent, with clusters featuring an -O-Au site exhibiting a preference for adsorption. The charges on small gold oxide clusters significantly impact the interaction strength and the activation degree of adsorbed O2: in the case of anionic cluster, the interaction between O2 and the -O-Au sites leads to a chemical reaction involving electron transfer, thereby significantly activating O2; in neutral and cationic clusters, the adsorption of O2 on their -O-Au sites can be viewed as an electrostatic interaction. Pointedly, for cationic clusters, the highly concentrated positive charge on the Au atom of the -O-Au sites can strongly adsorb but hardly activate the adsorbed O2. These results have certain reference points for understanding the gold oxide interfaces and the improved catalytic oxidation performance of gold-based systems in the presence of atomic oxygen species.

The size-dependent influence of palladium doping on the structures of cationic gold clusters

The physicochemical properties of small metal clusters strongly depend on their precise geometry. Determining such geometries, however, is challenging, particularly for clusters formed by multiple elements. In this work, we combine infrared multiple photon dissociation spectroscopy and density functional theory calculations to investigate the lowest-energy structures of Pd doped gold clusters, PdAu _n-1 ⁺ (n ≤ 10). The high-quality experimental spectra allow for an unambiguous determination of the structures adopted by the clusters. Our results show that the Pd-Au interaction is so large that the structures of PdAu _n-1 ⁺ and Au _n ⁺ are very different. Pd doping induces a 2D to 3D transition at much smaller cluster sizes than for pure Au _n ⁺ clusters. PdAu _n-1 ⁺ clusters are three-dimensional from n = 4, whereas for Au _n ⁺ this transition only takes place at n = 7. Despite the strong Au-Pd interaction, the Au _n-1 ⁺ cluster geometries remain recognizable in PdAu _n-1 ⁺ up to n = 7. This is particularly clear for PdAu₆ ⁺. In PdAu₈ ⁺ and PdAu₉ ⁺, Pd triggers major rearrangements of the Au clusters, which adopt pyramidal shapes. For PdAu₄ ⁺ we find a geometry that was not considered in previous studies, and the geometry found for PdAu₈ ⁺ does not correspond to the lowest-energy structure predicted by DFT, suggesting kinetic trapping during formation. This work demonstrates that even with the continuous improvement of computational methods, unambiguous assignment of cluster geometries still requires a synergistic approach, combining experiment and computational modelling.