Thiolate protected metal clusters are valuable precursors for the design of tailored nanosized catalysts. Their performance can be tuned precisely at atomic level, e. g. by the configuration/type of ligands or by partial/complete removal of the ligand shell through controlled pre‐treatment steps. However, the interaction between the ligand shell and the oxide support, as well as ligand removal by oxidative pre‐treatment, are still poorly understood. Typically, it was assumed that the thiolate ligands are simply converted into SO2, CO2 and H2O. Herein, we report the first detailed observation of sulfur ligand migration from Au to the oxide support upon deposition and oxidative pre‐treatment, employing mainly S K‐edge XANES. Consequently, thiolate ligand migration not only produces clean Au cluster surfaces but also the surrounding oxide support is modified by sulfur‐containing species, with pronounced effects on catalytic properties.

Atomically precise thiolate protected Au nanoclusters Au 38 (SC 2 H 4 Ph) 24 on CeO 2 were used for in-situ (operando) extended X-ray absorption fine structure/diffuse reflectance infrared fourier transform spectroscopy and ex situ scanning transmission electron microscopy−high-angle annular dark-field imaging/X-ray photoelectron spectroscopy studies monitoring cluster structure changes induced by activation (ligand removal) and CO oxidation. Oxidative pretreatment at 150 °C "collapsed" the clusters' ligand shell, oxidizing the hydrocarbon backbone, but the S remaining on Au acted as poison. Oxidation at 250 °C produced bare Au surfaces by removing S which migrated to the support (forming Au + -S), leading to highest activity. During reaction, structural changes occurred via COinduced Au and O-induced S migration to the support. The results reveal the dynamics of nanocluster catalysts and the underlying cluster chemistry.

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Doping gold nanoclusters with palladium has been reported to increase their catalytic activity and stability. PdAu 24 nanoclusters, with the Pd dopant atom located at the center of the Au cluster core, were supported on titania and applied in catalytic CO oxidation, showing significantly higher activity than supported monometallic Au 25 nanoclusters. After pretreatment, operando DRIFTS spectroscopy detected CO adsorbed on Pd during CO oxidation, indicating migration of the Pd dopant atom from the Au cluster core to the cluster surface. Increasing the number of Pd dopant atoms in the Au structure led to incorporation of Pd mostly in the S–(M–S) n protecting staples, as evidenced by in situ XAFS. A combination of oxidative and reductive thermal pretreatment resulted in the formation of isolated Pd surface sites within the Au surface. The combined analysis of in situ XAFS, operando DRIFTS, and ex situ XPS thus revealed the structural evolution of bimetallic PdAu nanoclusters, yielding a Pd single-site catalyst of 2.7 nm average particle size with improved CO oxidation activity.

Monolayer protected Au nanocluster catalysts are known to undergo structural changes during catalytic reactions, including dissociation and migration of ligands onto the support, which strongly affects their activity and stability. To better understand how the nature of ligands influences the catalytic activity of such catalysts, three types of ceria supported Au nanoclusters with different kinds of ligands (thiolates, phosphines and a mixture thereof) have been studied, employing CO oxidation as model reaction. The thiolate-protected Au 25 /CeO 2 showed significantly higher CO conversion after activation at 250 °C than the cluster catalysts possessing phosphine ligands. Temperature programmed oxidation and in situ infrared spectroscopy revealed that while the phosphine ligands seemed to decompose and free Au surface was exposed, temperatures higher than 250 °C are required to efficiently remove them from the whole catalyst system. Moreover, the presence of residues on the support seemed to have much greater influence on the reactivity than the gold particle size.

Ligand engineering of immobilized nanoclusters on surfaces: ligand exchange reactions with supported Au 11 (PPh 3 ) 7 Br 3 Au 11 nanoclusters immobilized on an alumina surface have shown to be accessible to ligand sphere transformations by thiolates in an aqueous environment. In contrast to the same ligand exchange in solution, the number of metal atoms in the core is preserved. This enables modifi cations of the nanocluster's structure and properties even after surface immobilization, e.g., by inducing photoluminescence through binding of fl uorescent thiolates.The properties of gold nanoclusters, apart from being size-dependent, are strongly related to the nature of the protecting ligand. Ligand exchange on Au nanoclusters has been proven to be a powerful tool for tuning their properties, but has so far been limited to dissolved clusters in solution. By supporting the clusters previously functionalized in solution, it is uncertain that the functionality is still accessible once the cluster is on the surface. This may be overcome by introducing the desired functionality by ligand exchange after the cluster deposition on the support material. We herein report the first successful ligand exchange on supported (immobilized) Au 11 nanoclusters. Dropcast films of Au 11 (PPh 3 ) 7 Br 3 on planar oxide surfaces were shown to react with thiol ligands, resulting in clusters with a mixed ligand shell, with both phosphines and thiolates being present. Laser ablation inductively coupled plasma mass spectrometry and infrared spectroscopy confirmed that the exchange just takes place on the cluster dropcast. Contrary to systems in solution, the size of the clusters did not increase during ligand exchange. Different structures/compounds were formed depending on the nature of the incoming ligand. The feasibility to extend ligand engineering to supported nanoclusters is proven and it may allow controlled nanocluster functionalization. † Electronic supplementary information (ESI) available: Detailed description of the experimental procedures, UV-Vis and MALDI-MS spectra of the ligand exchanges in solution, additional MALDI-MS, LA-ICP-MS, PL, PM-IRRAS and ATR-IR spectra of the ligand exchange on the surface, TEM images of the clusters and the discussion of another ligand exchange on the surface with 2-PET under different conditions. See Scheme 1 Left (1): Ligand exchange reactions of Au 11 (PPh 3 ) 7 Br 3 in solution with GSH (1a) and 2-PET (1b). Right (2): Ligand exchange reactions of supported Au 11 (PPh 3 ) 7 Br 3 with GSH (2a) and 2-PET (2b). Color code: Au = , P = , S = , Br = , O = , and N = . The organic ligand framework of the cluster structures after exchange is not shown.

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Nanometer-sized and stable thiolate-protected cobalt clusters were synthesized by a wet chemical method, leading to a pink solution with well-defined optical activity (UV-Vis) and photoluminescence (PL). The cobalt cluster core of ~1.3 nm size was metallic (as indicated by STEM, STM, XPS, HAADF-EELS) and was surrounded by a specific configuration of thiolate 2 staples (according to Raman, FTIR, XAFS, MALDI) that is similar to that of corresponding gold clusters.