High-surface-area catalyst design: Synthesis, characterization, and reaction studies of platinum nanoparticles in mesoporous SBA-15 silica
High-surface-area catalyst design: Synthesis, characterization, and reaction studies of platinum nanoparticles in mesoporous SBA-15 silica
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DOI：
10.1021/jp048867x
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发表时间：
2005-02-17
影响因子：
3.3
通讯作者：
Somorjai, GA
中科院分区：
文献类型：
--
作者：
Rioux, RM;Song, H;Somorjai, GA
采用醇还原法制备了尺寸为1.7 ~ 7.1 nm的铂纳米颗粒。一种聚合物（聚乙烯吡咯烷酮），PVP)被用来通过在水溶液中覆盖来稳定颗粒。采用x射线衍射（XRD）和透射电子显微镜（TEM）对颗粒进行了表征。透射电镜研究表明，颗粒的尺寸分布较窄。采用水热法合成了孔径为9 nm的介孔SBA-15二氧化硅，并将其用作催化剂载体。通过低功率超声将催化剂掺入介孔SBA-15二氧化硅中，煅烧去除纳米颗粒表面的稳定聚合物，并用H-2还原。用选择性气体吸附法测定的铂颗粒尺寸比用XRD和TEM等体积法测定的铂颗粒尺寸要大。选择室温乙烯加氢反应作为模型反应来考察Pt/SBA-15材料的活性。结果表明，该反应对粒径在1.7 ~ 3.6 nm之间的Pt/SBA-15材料结构不敏感。在1.7 ~ 7.1 nm范围内，乙烷在Pt颗粒上的氢解反应具有弱结构敏感性，较小的颗粒具有较高的比活性。乙烷氢解的周转率随着金属分散度的增加而单调增加，这表明小颗粒中的配位不饱和金属原子比大颗粒中的低指数平面对C2H6氢解更活跃。提出了结构敏感性的解释，并讨论了这些新型负载型纳米催化剂在进一步研究结构-活性和结构-选择性关系方面的潜在应用。
Platinum nanoparticles in the size range of 1.7-7.1 nm were produced by alcohol reduction methods. A polymer (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 silica with 9-nm pores was synthesized by a hydrothermal process and used as a catalyst support. After incorporation into mesoporous SBA-15 silica using low-power sonication, the catalysts were calcined to remove the stabilizing polymer from the nanoparticle surface and reduced by H-2. Pt particle sizes determined from selective gas adsorption measurements are larger than those determined by bulk techniques such as XRD and TEM. Roomtemperature ethylene hydrogenation was chosen as a model reaction to probe the activity of the Pt/SBA-15 materials. The reaction was shown to be structure insensitive over a series of Pt/SBA-15 materials with particle sizes between 1.7 and 3.6 nm. The hydrogenolysis of ethane on Pt particles from 1.7 to 7.1 nm was weakly structure sensitive with smaller particles demonstrating higher specific activity. Turnover rates for ethane hydrogenolysis increased monotonically with increasing metal dispersion, suggesting that coordinatively unsaturated metal atoms present in small particles are more active for C2H6 hydrogenolysis than the low index planes that dominate in large particles. An explanation for the structure sensitivity is suggested, and the potential applications of these novel supported nanocatalysts for further studies of structure-activity and structure-selectivity relationships are discussed.