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Organic Polymers, Oligomers, and Catalysis
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Metal clusters, defined as particles smaller than 2 nm and composed of less than 100 atoms, are anticipated to provide new catalytic properties because of their unique size and electronic structure. At the moment, Pd, Au and Pt polymer-supported nanoclusters have been the most studied ones. Their in situ synthesis strongly depends on both the nature of the polymer and the reducer reagent chosen. As a stabilizing material, the polymer should interact strongly with nanoclusters enough to prevent their aggregation but not too strongly to avoid their deactivation [178].Polymers containing benzene and other cyclic aromatic moieties provide generally the adequate interaction [179].The polymeric matrix is typically obtained by reticulation: cross-linking moieties, for instance epoxy groups, are thus required in the polymer structure [180–183].To avoid the growth of larger NPs, in situ reduction of metal ions is performed with a strong reducing reagent (like NaBH4) with an excess of polymeric coordination sites compared to metal ions [184].
Metal Clusters on Oxides
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
Clusters of metal atoms on an oxide support can be investigated with an array of surface-science techniques by using model systems of a metal evaporated onto an oxide thin film. This film, in turn, is supported on a refractory metal surface. The cohesive energies of the metal clusters can be determined with thermal desorption spectroscopy. In general, small metal clusters have smaller cohesive energy than bulk materials. The surface structure of metal clusters can be studied with STM, AFM, and IRAS using probe molecules. The catalytic properties and metal-support interaction of supported metal clusters can be explored with surface spectroscopies and reaction kinetics measurements in a combined elevated pressure reactor and UHV surface analysis system.
Density Functional Theory Studies for Catalysis of Atomically Precise Metal Clusters
Published in Yan Zhu, Rongchao Jin, Atomically Precise Nanoclusters, 2021
Metal clusters exhibit unique physical and chemical properties, such as high surface-to-volume ratio, high catalytic activity, and tunability, and thus show significant prospects in energy and environmental applications [1]. The utilization of metal clusters, however, is unfortunately limited by their intrinsic features. For example, metal clusters are too reactive to be separated and stored. It is also difficult to obtain a pure metal cluster with monodisperse molecular structure and consistent properties. Recently, advances in the synthesis of atomically precise metal clusters [2, 3] have shown promises to overcome some of these challenges. An atomically precise metal cluster has a well-defined crystal structure comprising a metal cluster core and a shell of protective organic ligands. The metal cluster core can be considered as a superatom, where the occupancy of valence electrons may follow general rules similar to the 8-electron rule for main group atoms and the 18-electron rule for transition metal atoms. Because of the occupation rules, the metal cluster core exhibits a preference to incorporate a certain number of protective ligands and hence achieves the atomically precise structure. On the other hand, the protective ligands can fully or partially passivate the metal cluster core, which allows for the separation, storage, processing, and utilization of metal clusters. The crystal structure for [Ag25(SPhMe2)18]− [4], a thiolated silver cluster, is shown in Fig. 10.1. [Ag25(SPhMe2)18]− consists of an Ag13 icosahedron core and six SR(AgSR)2 staples at precise surface positions of Ag13.
Structural evolution of dicarbon-silver cluster anions: from flat to 3-dimensional and from attached to core–shell
Published in Molecular Physics, 2023
Metal clusters are well known as versatile catalysts for a multitude of chemical processes. For reactions involving organic (carbon-based) molecules, the main places of action here are metal–carbon interfaces. For a more efficient catalysis, properties of metal clusters can be modified in terms of shape (via structure–property relationships) as well as electronic structure – in particular again via bringing them in contact with, e.g. carbon. Examples include metal clusters deposited on carbon surfaces (graphite, graphene, carbon nanotubes, etc.) or doped by, for instance, atomic/molecular carbon, which systems represent external and internal metal–carbon interfaces, respectively. Another property of interest for metal-based clusters is their optical parameters which can also be affected by the system composition and structure.
A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films
Published in Science and Technology of Advanced Materials, 2022
Ngan T. K. Nguyen, Clément Lebastard, Maxence Wilmet, Noée Dumait, Adèle Renaud, Stéphane Cordier, Naoki Ohashi, Tetsuo Uchikoshi, Fabien Grasset
Of course, this field of research is quite young and new challenges and opportunities using transition metal clusters as building blocks for multifunctional nanocomposites are numerous. This field can be extended to the use of other transition metal clusters, such as titanium, vanadium, copper, zirconium or event heterometallic systems as already started by Lebastard et al. [105,107,257–262]. This family of nanoclusters is extremely rich and could be even probably enriched by using machine learning methods [263–265]. Controlled self-assembly of nanoclusters could play a key role in customizing advanced functional materials via collective and synergetic properties between neighbored building blocks [266]. As briefly mentioned in the introduction, the condensation and dimensionality of the metal atom clusters influence strongly the electronic properties and an association with an adequate matrix could generate new nanocomposites. For instance, the mixing of MCs with semiconductor nanocrystals could also be very interesting for photovoltaic applications. Moreover, to increase the dimensionality of the metal atom clusters could be very interesting in terms of thermal stability for instance, which is still a weak point for the molecular nanoclusters.