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N. Barrabés-Rabanal:
"Atomically Designed Catalysts by Bimetallic Metal Nanoclusters: insights into the structure dynamics by operando spectroscopy";
Hauptvortrag: Cluster Meeting 2021, Prague (eingeladen); 18.07.2021 - 23.07.2021.

In nanocatalysis, a great challenge is to obtain truly homogenous and well-defined highly active nanostructures on surfaces. An emerging class of functional nanomaterials with atomic precision, well-defined molecular structure, and intriguing molecular-like properties are the ligand protected metal nanoclusters. The outstanding size control during the cluster synthesis, opens new opportunities for accurate studies of size-dependent properties, atomic structure effects, and reaction mechanisms in catalysis. Understanding of the cluster-surface interactions is a fascinating topic of research, still in its infancy. In our recent work, in situ XAS and IR measurements revealed the strong influence of the cluster structure and support material in their stability and reactivity in different gas and liquid phase reactions.[1-3]
The physical-chemical properties of gold nanoclusters can be fine-tuned by heteroatom doping, which has a strong influence on their stability and reactivity. Knowledge of the number of incorporated dopant atoms, their exact location in the cluster, as well as structure-property relationships is required for a thorough understanding.
In our recent work, we demonstrated the dynamic structure of Pd-doped Au25 nanoclusters upon pretreatment and CO oxidation reaction. When one Pd atom was doped into the center of a Au25 cluster, a combination of oxidative and reductive pretreatment was required to obtain maximum CO oxidation activity. This was related to the migration of the Pd atom to the surface of the cluster core. It was observed by operando DRIFTS spectroscopy displaying a CO-Pd vibrational band, characteristic of single site bonding. Furthermore, in situ XAFS studies confirmed it displaying PdAu alloy formation but not Pd-Pd bonds were detected, revealing that isolated Pd single sites were present on the cluster surface. Similar behavior was also observed in the case of Ag doped Au25 nanoclusters supported on zeolites.
Thus, the evolution of the doped Au clusters to nanoalloys with single atom surface sites was revealed by combined XAFS, DRIFTS and XPS studies. Overall, these studies contributes to a better understanding of the dynamics of supported doped nanoclusters upon pretreatment and reaction, which is a key information for future design and application of bimetallic nanocluster catalysts.