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| - High-Surface-Area Catalyst Design: Synthesis, Characterization, and Reaction Studies ofPlatinum Nanoparticles in Mesoporous SBA-15 Silica
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| - Platinum nanoparticles in the size range of 1.7−7.1 nm were produced by alcohol reduction methods. Apolymer (poly(vinylpyrrolidone), PVP) was used to stabilize the particles by capping them in aqueous solution.The particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM).TEM investigations demonstrate that the particles have a narrow size distribution. Mesoporous SBA-15 silicawith 9-nm pores was synthesized by a hydrothermal process and used as a catalyst support. After incorporationinto mesoporous SBA-15 silica using low-power sonication, the catalysts were calcined to remove the stabilizingpolymer from the nanoparticle surface and reduced by H2. Pt particle sizes determined from selective gasadsorption measurements are larger than those determined by bulk techniques such as XRD and TEM. Room-temperature ethylene hydrogenation was chosen as a model reaction to probe the activity of the Pt/SBA-15materials. The reaction was shown to be structure insensitive over a series of Pt/SBA-15 materials with particlesizes between 1.7 and 3.6 nm. The hydrogenolysis of ethane on Pt particles from 1.7 to 7.1 nm was weaklystructure sensitive with smaller particles demonstrating higher specific activity. Turnover rates for ethanehydrogenolysis increased monotonically with increasing metal dispersion, suggesting that coordinativelyunsaturated metal atoms present in small particles are more active for C2H6 hydrogenolysis than the lowindex planes that dominate in large particles. An explanation for the structure sensitivity is suggested, andthe potential applications of these novel supported nanocatalysts for further studies of structure−activity andstructure−selectivity relationships are discussed.
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