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Supported metal atoms and

Each surface defect has a direct and characteristic effect on the properties of adsorbed species. This becomes particularly important in the analysis of the chemical reactivity of supported metal atoms and clusters [12,13]. The defects not only act as nucleation centers in the growth of metal islands or clusters [14,15], but they can also modify the catalytic activity of the deposited metal by affecting the bonding at the... [Pg.183]

The extended fine structure (EXAFS) was used to determine bond distances, coordination number and disorder. The near edge (XANES) was used as an Indication of electronic state. Significant results Include, 1) a reversible change of shape of clean supported metal clusters as a function of temperature, 2) supported Pt clusters have more disorder or strain compared to the bulk metal, and 3) a clear determination of the bonds between the catalytic metal atoms and the oxygen atoms of the support. [Pg.280]

Dynamic Processes of Metal Atoms and Small Metal Clusters in Solid Supports... [Pg.292]

Surface morphology is expected to be crucial when reacting an organometallic compound with such particles. It will depend on particle size as well as other parameters such as the exposed planes of the support (e.g., by epitaxy). Metal particles of various sizes are composed of zero valent metal atoms, and these atoms have different natures, depending on their location in the core or at the surface of the particles. The active centers are located at the periphery of the particle. The... [Pg.56]

Arrhenius parameters for the methanation reaction on alumina-supported Group VIII metals (227b) were close to the line for cracking reactions on several metals (Table III, A). Activity was based on the numbers of surface metal atoms and a compensation relation was described from these data we calculate c = 0.1185 0.0117, B = 15.216 1.068, and oL = 0.491. [Pg.289]

The EXAFS results have implications for the metal support interaction. The data in Table 9.1 indicate that the main interaction between rhodium and alumina occurs between reduced metal atoms and two to three oxygen ions in the surface of the support at a distance of 0.27 nm. It appears logical, therefore, to attribute the metal support interaction to bonding between oxygen ions of the support and induced dipoles inside the rhodium particle [19]. Although such bonding is weak on a per atom basis, the cumulative bond for the whole particle may be significant. [Pg.259]

Sintering is an important mode of deactivation in supported metals that involves complex microscopic physical and chemical phenomena, e.g., dissociation, emission, diffusion, and capture of metal atoms and crystallites. The relative importance of these different processes may change with reaction conditions and catalyst formulation. Modeling and prevention of sintering processes require an understanding of these basic processes as well as quantitative measurements of sintering rates. [Pg.16]

In the past five years, the field of metal-zeolite chemistry has developed to the point where a number of metal atomic and small cluster guests have been synthesized and unequivocally characterized by spectroscopic and crystallographic techniques. The silver-zeolite A, X and Y systems in particular have yielded a wealth of valuable structural and site information pertaining to silver guests in the size range of one to six atoms (3). The spectroscopy of these silver-zeolites can therefore be probed in detail and compared with the corresponding data for silver atoms and silver clusters immobilized in weakly interacting rare gas solid supports (4). [Pg.410]


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Strong metal-support interactions (SMSI) and electronic structures In situ atomic resolution ETEM

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