The preparation and characterization of highly dispersed metal nanoparticles in mesoporous silica SBA-15 are reported. The functionalization with organosilane to generate a monolayer of charged groups on the pore surface facilitates uniform distribution of ionexchanged metal precursors in the channels of SBA-15, which, upon reduction, results in highly dispersed metal nanoparticles supported in SBA-15. Under mild reduction conditions, the surface functionality remains and so allows further metal incorporation cycles to achieve higher metal loading. After reduction in hydrogen flow, disk-shaped Pt nanoparticles in Pt/ SBA-15 and spherical Au nanoparticles in Au/SBA-15 have been characterized in the channels of SBA-15 by PXRD, XAS, and TEM. Secondary Pt incorporation in Au/SBA-15 produces coexisting small Pt nanoparticles with large Au nanoparticles in the host channels. This preparation method is capable of template synthesis of various metal nanostructures with controlled morphology and composition inside the channels of mesoporous materials.
The activation of a dimethylgallium/ZSM-5 precursor to well-defined reduced and oxidized species is studied by in situ Ga K edge XANES. The precursor is prepared by chemical implanting of trimethylgallium on acidic HZSM-5. Subsequent reduction leads to charge-compensating Ga + species. Direct oxidation of the trimethylgallium precursor leads to various forms of gallium oxide and regeneration of Brønsted acid protons. Oxidation of the reduced Ga + species yields predominantly to GaO + species. The GaO + species exhibit a much higher H 2 /D 2 exchange activity than reduced Ga + species.
Characterization of mesoporous thin films and its implication in applications are presented in this report. It was found that optical, electrical and mechanical properties of mesoporous thin films prepared through surfactant templating are dependent on the film thickness, porosity, pore size and pore structure. A good understanding of the film properties thus becomes crucial to have a good handle on the electronic and optical applications of these materials.
Platinum nanoparticles, nanorods, and nanonetworks were fabricated in mesoporous silica MCM-48. Investigations including transmission electron microscopy (TEM) with electron diffraction, powder X-ray diffraction (PXRD) with Rietveld analysis, and extended X-ray absorption fine structure analysis (EXAFS) suggest the crystal growth mechanism, packing arrangement, and oxidative capability of confined nanostructured metal in the MCM-48 host with a three-dimensional channel structure and cubic Ia3d symmetry.
The structures and the chemical nature of gallium species in gallium-containing zeolite catalysts prepared by hydrothermal synthesis and post-synthesis treatments are discussed based on the results of X-ray absorption spectroscopy (XAS), including X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS), and nuclear magnetic resonance (NMR) investigations. The in-situ analysis of properties of gallium active sites during oxidation/reduction cycles has been found to be further helpful on the understanding of the catalytic role of gallium species in the aromatization of alkanes.
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