Au/SiO2纳米复合粒子的合成及其催化应用的研究

菜单

摘要Au、Ag、Pt和Pd等贵金属纳米粒子因其优异的催化性能而受到广泛关注。但是贵金属纳米粒子尺寸小、比表面积大，易发生团聚，而团聚将使其催化活性严重劣化。将贵金属纳米粒子负载于多孔的无机纳米载体上，能提高贵金属纳米粒子的分散性，使其保持高的催化活性。本论文提出了一种基于无机前驱物反相细乳液溶胶—凝胶反应和贵金属盐原位还原技术的制备贵金属/无机多孔载体纳米复合粒子的新方法，并对材料的制备过程、材料的结构及其催化性能进行了系统研究。47237

在以HAuCl4极性溶液为液滴的反相细乳液体系中，通过正硅酸乙酯的溶胶－凝胶过程，制得了HAuCl4/SiO2纳米复合粒子；然后再在纳米复合粒子内部原位将金盐原位还原，制得高催化活性的Au/SiO2纳米复合粒子。研究发现：Au/SiO2纳米复合粒子亦为球形粒子，且Au纳米粒子主要分布于SiO2载体的表面。在0.043-0.17g的范围内，随HAuCl4装载量的增加，纳米复合粒子的尺寸先下降，后基本不变；Au纳米粒子的尺寸则从10nm增加至18nm。不同HAuCl4装载量的纳米复合粒子中，SiO2纳米载体的吸脱附曲线均为I—B型等温线，说明其具有微孔结构。SiO2纳米载体的比表面均高于330m2·g-1，装载量为0.17g时，比表面积甚至高达550 m2·g-1。以硼氢化钠还原对硝基苯酚的反应为模型反应，评估了Au/SiO2纳米复合粒子的催化活性。研究发现：Au纳米粒子的尺寸是决定Au/SiO2纳米复合粒子催化性能的主要因素，在本研究的范围内，随Au纳米粒子粒径下降，Au/SiO2纳米复合粒子催化活性增加；随反应温度增加，催化反应速率先增加后略有下降，在20~40°C范围内，反应的表观活化能为35.7kJ·mol-1。

本论文所提出的制备方法有很好的通用性和灵活性，有望成为制备此类具有复杂形态的纳米复合粒子的通用技术。

毕业论文关键字：反向细乳液；贵金属纳米粒子；溶胶—凝胶过程；原位还原；纳米复合粒子；化学催化

Abstract

Noble metal nanoparticles (NPs), such as Au, Ag, Pt and Pd NPs, have attracted wide attention owing to their excellent optical and catalytic properties. However, noble metal NPs are inclined to undergo agglomeration due to their small size, large surface area and surface energy. The agglomeration of noble metal NPs leads to a serious deterioration of their catalytic activity. The dispersion and catalytic properties of noble metal NPs may be improved through immobilization of noble metal NPs on a porous inorganic nano-support.

HAuCl4/SiO2 NCPs were prepared through a sol–gel process of tetraethyl orthosilicate in inverse miniemulsions with the polar solution of HAuCl4 as droplets. The incorporated gold salts were reduced on the surface of the SiO2 nanosupports to obtain Au/SiO2 NCPs. The Au NPs were mainly distributed onto the surface of the SiO2 nano-supports. With the increase of the HAuCl4 loading from 0.043g to 0.17g, the particle size of the Au/SiO2 NCPs decreased first and then remained constant, the particle size of Au NPs increased from 10 nm to 18 nm. The isotherms of the SiO2 nano-supports with various HAuCl4 loadings were I–B type isotherm, indicating the presence of microporous structures. The specific surface areas of the SiO2 nano-supports with various HAuCl4 loadings were all larger than 330 m2·g-1. Especially, the SiO2 nano-support with 0.17 g of the HAuCl4 loading was 550 m2·g-1. The reduction of p-nitrophenol (p-NPh) with sodium borohydride was used as the model reaction to evaluate the catalytic activity of Au/SiO2. The results indicate that determining factor of the catalytic activity of the Au/SiO2 NCPs is the particle size of Au NPs. Within the scope of this study, the catalytic activity of the Au/SiO2 NCPs decreased with the increase of the particle size of Au NPs. The reaction rate increased with the increase of the temperature from 20 °C to 40 °C, and the apparent activation energy in this temperature range was 35.7 kJ·mol-1. Further increase of the reaction temperature leaded to a slight decrease in the reaction rate.