多元醇法合成銅鉑奈米粒子特性鑑定與觸媒性質之研究

Abstract

金屬奈米粒子由於其具有與塊材截然不同的性質，近年來成為最熱門的研究課題之ㄧ。其中，奈米粒子具有相當大的比表面積，故其在觸媒上的應用相當受到矚目。而二元金屬奈米粒子加上了成分與結構的變化，而使得更有改進其觸媒性質的潛力。 銅鉑奈米粒子一直以來是相當優異的觸媒，然而大多數的研究皆以合金型為主。由於觸媒作用只發生在奈米粒子的表面，我們相信研究銅鉑核殼型奈米粒子在觸媒的應用上相當具有商業化的價值。因此，本研究利用多元醇法製備了一系列成分的銅鉑合金型及核殼型奈米粒子，探討成分對於粒子結構及形態的影響。而銅鉑奈米粒子催化丙烯腈水合反應的產率，則是作為判斷其觸媒好壞與否的指標。 本研究利用HRTEM、EDS、XRD及UV-vis吸收光譜對於合成出的奈米粒子做特性的鑑定。由HRTEM可以觀察到我們所製備的銅鉑核殼型奈米粒子在粒子的表面具有對比較深的情形，而UV-vis吸收光譜也顯示了銅的吸收峰訊號被遮蔽，更證明了我們的確製備出核殼型粒子。更重要的是，沒有任何研究曾指出此現象。同時，在核殼型系統中，不論成分為何，粒徑超過10 nm的粒子會生長成六角形。這在結構的觀點上是相當有趣的現象。而利用HPLC分析丙烯腈在80℃下經過銅鉑奈米粒子催化後的結果，發現不論是合金型或是核殼型銅鉑奈米粒子，其效率皆高於純銅奈米粒子。證明在白金的添加下，對於整體的觸媒活性具有相當大的改善。由於貴金屬對於此反應為惰性，此種加成效果更說明了二元金屬奈米粒子對於彼此的電子組態的確造成了變化，導致其觸媒性質起了修飾的作用。

Study of metal nanoparticles has become one of the hottest research topics in these years, because their properties are quite different from bulk materials. Since they have large specific surface area, nanoparticles are noticeable in catalytic applications. Furthermore, bimetallic nanoparticles, alloy or core-shell, provide higher potential to modify catalytic properties due to the variation in composition and structure. Cu-Pt nanoparticles have been used as excellent catalysts for a long time, but the greater part of studies focus on alloy nanoparticles. Because catalysis only reacts at the surface of nanoparticles, we believe that research on catalytic application of Cu-core Pt-shell nanoparticles is extremely valuable for commercialization. Therefore, we synthesize a series of Cu-Pt alloy and core-shell nanoparticles by polyol method to investigate the effect of composition on structure and morphology of particles in this work. In addition, their catalytic abilities were determined by the yield of hydration reaction of acrylonitrile catalyzed by Cu-Pt nanoparticles. In our work, characterization of Cu-Pt nanoparticles was obtained by HRTEM, EDS, XRD, and UV-vis absorption spectrum. Core-shell structures were confirmed by the dark contrast at the surfaces of nanoparticles observed in HRTEM images and the vanish of UV-vis absorption peak of Cu. More importantly, there wasn’t any study ever pointed out these phenomena. Moreover, in core-shell system, particles will grow into a hexagonal shape when their sizes larger than 10 nm in whole range of compositional change. It’s interesting from the structure viewpoint. This study also proves that the addition of platinum will highly improve the catalytic activity of copper. Using HPLC to analyse the hydration reaction catalyzed by Cu-Pt nanoparticles at 80℃, it can be clearly seen that the efficiency of alloy and core-shell nanoparticles are better than copper nanoparticles. Since noble metals are inert as the catalyst for this reaction, the enhancement of catalytic activity accompanies with the change of electronic structure of bimetallic nanoparticles. Further, the catalytic property is tailored.