Metal clusters on supports: synthesis, structure, reactivity, and catalytic properties

Abstract

This review of structurally simple and essentially molecular metal clusters on solid supports addresses synthesis, characterization, reactivity, and catalysis. Examples of supported clusters made in high yields are Os(3), Ir(4), Ir(6), and Rh(6), and typical supports are MgO, gamma-Al(2)O(3), and zeolites. Supported clusters are synthesized by adsorption of ligated molecular metal clusters, deposition of bare size-selected metal clusters from the gas phase, and adsorption of metal complexes followed by treatment to form clusters. Some metal clusters on supports have been imaged with atomic resolution. Reactions of supported metal clusters include ligand modifications, oxidative fragmentation, and migration leading to aggregation. Reactivities and catalytic properties of the clusters (e.g., for alkene hydrogenation and epoxidation) depend on the cluster size and the support (which acts as a ligand) and are distinct from those of supported particles that resemble bulk metals. Opportunities for deeper understanding of the chemistry of supported metal clusters hinge on improvements in characterization techniques such as X-ray absorption spectroscopy and high-resolution transmission electron microscopy.

Simulating the Complexities of Heterogeneous Catalysis with Model Systems: Case studies of SiO2 Supported Pt-Group Metals

“…The primary aim of these approaches is to exert greater control over characteristic(s) of the catalyst surface, such as metal cluster or particle size, particle uniformity, alloy composition, and/or complexity of the catalyst support. For example, pioneering work by Gates and co-workers have demonstrated that the deposition of well-defined metal clusters on catalyst supports can be utilized as a technique to generate surfaces containing active clusters with well defined coordination and structure [12][13][14]. Clusters can be deposited via mononuclear precursor techniques (such as Rh(CO) 2 (acac)) or via molecular cluster precursors to generate surfaces preserving a specific metal cluster structure (for example Ir 4 (CO) 12 to generate Ir 4 clusters) [12,13].…”

Morphology and stability of Au nanoclusters in HOPG nanopits of well-defined depth

“…This results in a strongly anisotropic distribution of nanoparticles on the surface like metallic chains [15], a difficult size control and even more important in a small particle density. An important issue in this context is to find a a e-mail: wolfgang.harbich@epfl.ch way to stabilize these nanostructures [18][19][20][21]. A possible way is to pin the particles via the creation of defects to the surface [22][23][24][25][26][27][28].…”

Pure and Zn-doped Pt clusters go flat and upright on MgO(100)

“…The catalytic properties of such nanometer and subnanometer clusters can be outstanding, but depend strongly and nonlinearly on cluster size and composition, [1][2][3][4][5][6][7] and also on the nature of the support. 6,[8][9][10][11][12][13] The electronic structure of clusters is reminiscent of molecules, in that important chemical-physical properties can be understood from a molecular orbital (MO) picture, wherein the MOs will be well-separated in energy, rather than having continuous energy bands. 14,15 The support plays the role of a ligand in very small (o1 nm) clusters, capable of actively modifying cluster structures, charge, and other properties (see e.g.…”