钯、铂、金基纳米催化剂的制备及其性能研究

发布时间：2018-09-05 20:43

【摘要】：贵金属纳米材料因其独特的物理化学性能和在催化领域的优异表现,目前已成为现代化学研究的热点之一。贵金属纳米材料的催化活性与其组成、尺寸和形貌等密切相关,我们可以通过调控这些因素来提高其催化活性。一般来说比表面积越大,纳米材料的催化活性就越高。然而,较高的比表面积常会使贵金属纳米材料在催化过程中发生团聚而导致其催化活性的降低,同时,考虑到贵金属价格昂贵的特殊性,因此开发出具有高稳定性的贵金属纳米催化剂是十分必要的。尽管人们已经采取不同的方法合成了一系列的贵金属纳米催化剂,但这些方法通常具有反应条件苛刻、复杂、不易大规模生产等缺陷,难以推广到实际应用中。因此,本论文致力于发展一种简单、快速、实用的方法来制备具有高活性和高稳定性的贵金属纳米催化剂,并采用Suzuki偶联反应、硅烷的氧化和对硝基苯酚的还原等几个催化反应对所制备的催化剂的性能进行评价。(1)制备γ-Al2O3负载的高分散的Pd纳米催化剂,并研究了它对Suzuki偶联反应、硅烷氧化反应的催化性能。我们采用室温下CO还原已浸渍于γ-Al2O3上的PdCl2来制备Pd纳米催化剂(Pd298K/γ-Al2O3)。由于我们的反应温度为室温,条件较为温和,因此与传统高温氢气还原(773 K下空气煅烧和623 K下Ar/H2还原)所制备γ-Al2O3负载的Pd纳米催化剂(Pd773K/γ-Al2O3)相比,我们所制备的Pd298K/γ-Al2O3中Pd纳米催化剂具有尺寸较小,分散性好和粒径分布范围窄的优势。通过进一步的研究表明其对Suzuki偶联反应和硅烷的氧化反应的催化活性都比Pd773K/γ-Al2O3高。更重要的是,Pd298K/γ-Al2O3同时也具有较好的循环稳定性,5次循环后催化活性没有明显损失。(2)发展了一种简单、快速的方法来合成铂银多孔纳米球壳(PNSSs),并对其催化水相中硅烷氧化反应的催化性能进行了研究。首先,我们采用一步溶剂热法合成了Ag@Pt核-壳纳米球(CSNSs),在这里氨水和聚乙烯吡咯烷酮的加入对抑制AgCl沉淀的产生起到了至关重要的作用。随后用硝酸对Ag@Pt CSNSs进行选择性的腐蚀银核即得到我们所期望的PtAg PNSSs。经研究发现我们所制得的PtAg PNSSs是厚度约为3nm左右的多孔且表面粗糙的纳米球壳,这种特殊的结构使得PtAg PNSSs相对于商业Pt/C来说,在水中无论是对脂肪族硅烷还是芳香族硅烷的氧化都表现出了更优异的催化活性,并且这种中空无负载的结构也使其具有较高的循环稳定性,5次循环后催化活性没有明显损失。(3)制备Au-SiO2蛋黄-蛋壳(YSNSs)纳米结构,并以催化对硝基苯酚还原为模型对其催化性能进行了研究。与传统的三步法合成Au@M@SiO2纳米结构相比,我们采用一步溶剂热法合成了Au@Ag核-壳(CSNSs)纳米结构,再通过包覆二氧化硅就可得到Au@Ag@SiO2核-壳-壳纳米结构,然后我们对其进行硝酸腐蚀选择性去除银核即可得到我们所期待的Au-SiO2我们所制备的Au-SiO2 YSNSs对对硝基苯酚的还原表现出了良好的催化活性和循环稳定性,5次循环后催化活性没有明显损失。
[Abstract]:Noble metal nanomaterials have become one of the hotspots of modern research because of their unique physical and chemical properties and excellent catalytic performance in the field of catalysis. The catalytic activity of noble metal nanomaterials is closely related to their composition, size and morphology. We can improve their catalytic activity by adjusting these factors. Generally speaking, specific surface area However, high specific surface area often leads to the agglomeration of noble metal nanomaterials in the catalytic process, which leads to the reduction of their catalytic activity. At the same time, considering the expensive particularity of noble metals, it is necessary to develop noble metal nanocatalysts with high stability. Although a series of noble metal nanocatalysts have been synthesized by different methods, these methods usually have some disadvantages, such as harsh reaction conditions, complex reaction conditions, difficult mass production and so on, which make it difficult to be applied to practical applications. Qualitative precious metal nano-catalysts were used to evaluate the performance of the prepared catalysts by Suzuki coupling reaction, silane oxidation and p-nitrophenol reduction. (1) The highly dispersed Pd nano-catalysts supported on gamma-Al2O3 were prepared and their catalytic properties for Suzuki coupling reaction and silane oxidation were studied. Pd nanocatalysts (Pd298K/gamma-Al2O3) were prepared by CO reduction of PdCl2 impregnated on gamma-Al2O3 at room temperature. Since the reaction temperature was room temperature and the conditions were mild, the Pd nanocatalysts supported on gamma-Al2O3 (Pd773K/gamma-Al2O3) were prepared by conventional high temperature hydrogen reduction (air calcination at 773 K and Ar/H2 reduction at 623 K). Compared with Pd298K/gamma-Al2O3, Pd nanocatalyst prepared by us has the advantages of small size, good dispersion and narrow particle size distribution. Further studies show that its catalytic activity for Suzuki coupling reaction and silane oxidation is higher than that of Pd773K/gamma-Al2O3. More importantly, Pd298K/gamma-Al2O3 also has better catalytic activity. (2) A simple and rapid method was developed to synthesize platinum-silver porous nanosphere shells (PNSSs) and its catalytic performance for silane oxidation in aqueous phase was studied. Firstly, Ag @Pt core-shell nanospheres (CSNSs) were synthesized by one-step solvothermal method. The addition of ammonia and polyvinylpyrrolidone played an important role in inhibiting the formation of AgCl precipitation. Then the Ag @Pt CSNSs were selectively corroded with nitric acid to form the desired PtAg PNSS. The PtAg PNSS was found to be porous and rough nanospheres with a thickness of about 3 nm. Shell, this special structure makes PtAg PNSS exhibit superior catalytic activity for both aliphatic silane and aromatic silane oxidation in water compared with commercial Pt / C, and this hollow unsupported structure also makes PtAg PNSS have high cyclic stability. After five cycles, the catalytic activity is not significantly lost. Au-SiO2 yolk-eggshell (YSNSs) nanostructures were prepared and their catalytic properties were studied by catalytic reduction of p-nitrophenol. Compared with the traditional three-step synthesis of Au@M@SiO2 nanostructures, Au@Ag core-shell (CSNSs) nanostructures were synthesized by one-step solvothermal method, and then Au@Ag@SiO2 core-shell (CSNSs) nanostructures were prepared by coating silica. The shell-shell nanostructures were then corroded by nitric acid to selectively remove the silver nucleus, and the desired reduction of p-nitrophenol by the Au-SiO2 YSNSs prepared by US showed good catalytic activity and cyclic stability. There was no significant loss of catalytic activity after five cycles.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TB383.1

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