碳纳米管限域效应对肉桂醛选择加氢产物分布的影响（英文）

发布时间：2018-10-31 09:58

【摘要】：碳纳米管因其独特的电子结构和性能引起了研究者们广泛的兴趣,尤其是它有序的纳米级管腔结构,可以为催化剂和催化反应提供一种独特的一维限域环境.碳纳米管的限域效应主要由于其管腔几何和电子结构可以使反应物发生富集、对金属纳米颗粒的尺寸限制以及对电子结构的调变作用.一系列研究表明,碳纳米管的限域效应可以对催化剂的活性进行调变,但是对产物选择性的影响方面研究得较少,特别是管径小于4 nm的碳纳米管的限域体系.因此,本文以肉桂醛选择性加氢反应为探针,研究限域效应对产物选择性的影响规律.采用管径为1-3 nm的碳纳米管,基于气相填充的方法将Ru纳米团簇分散于碳纳米管的管腔中,得到碳纳米管限域的Ru催化剂(Ru@CNT);采用浸渍法制备了碳纳米管管外壁负载的催化剂(Ru/CNT)来进行对比.肉桂醛含有共轭的C=C和C=O键,由于C=C键能低于C=O,前者更易发生加氢反应.结果表明,分散在碳纳米管外壁的Ru催化剂可以催化肉桂醛中的C=C加氢,得到氢化肉桂醛(HCAL);而Ru@CNT催化剂不仅可以催化C=C加氢得到氢化肉桂醛HCAL,还可以催化C=O键加氢得到肉桂醇,以及氢化肉桂醇.通过高分辨透射电镜、拉曼、程序升温还原、程序升温脱附对催化剂进行了表征.发现碳纳米管限域的纳米团簇金属颗粒的粒径大约为1-2 nm,与管外负载的金属颗粒相近,但是Ru@CNT催化剂上仍有部分金属纳米团簇分布在管外壁,这可能是Ru@CNT催化剂上有C=C键加氢产物的一个原因.碳纳米管独特的限域效应促进了Ru物种的还原,在H_2气氛下管内Ru物种的还原温度比管外低20oC.金属与碳纳米管的内、外壁之间的电子相互作用,纳米管腔的空间限制作用及管腔富集作用可能是产物分布产生差异的原因.
[Abstract]:Because of its unique electronic structure and properties carbon nanotubes (CNTs) have attracted extensive interest especially their ordered nanotubes which can provide a unique one-dimensional confined environment for catalyst and catalytic reactions. The limiting effect of carbon nanotubes (CNTs) is mainly due to the enrichment of reactants due to the geometry and electronic structure of the tube cavity, the size limitation of metal nanoparticles and the modulation of electronic structure. A series of studies have shown that the limited effect of carbon nanotubes can adjust the activity of the catalyst, but the influence of the selectivity of the product is less than that of the carbon nanotubes, especially the limited system of carbon nanotubes with diameter less than 4 nm. Therefore, the selective hydrogenation of cinnamaldehyde was used as a probe to study the effect of limiter effect on the selectivity of the product. Carbon nanotubes (CNTs) with diameter 1-3 nm were dispersed in the cavity of CNTs by gas-phase filling method to obtain Ru catalysts (Ru@CNT) in carbon nanotubes (CNTs). The catalyst (Ru/CNT) supported on the outer wall of carbon nanotubes (CNTs) was prepared by impregnation method for comparison. Cinnamaldehyde contains conjugated C C and C O bonds. Because the C C bond energy is lower than that of C O, the former is more prone to hydrogenation. The results show that Ru catalyst dispersed on the outer wall of CNTs can catalyze the hydrogenation of CnC in cinnamaldehyde to obtain hydrogenated cinnamaldehyde (HCAL);. Ru@CNT catalyst can not only hydrogenate C to produce hydrogenated cinnamaldehyde HCAL, but also can catalyze the hydrogenation of C-O bond to cinnamol and hydrogenated cinnamol. The catalyst was characterized by high resolution transmission electron microscopy, Raman, temperature programmed reduction and programmed temperature desorption. It was found that the diameter of the metal particles in the carbon nanotubes was about 1-2 nm, and that the metal particles loaded outside the tubes were similar, but some metal nanoclusters were still distributed in the outer wall of the tubes on the Ru@CNT catalyst. This may be one of the reasons for the presence of C C bond hydrogenation products on Ru@CNT catalysts. The unique limiting effect of carbon nanotubes promotes the reduction of Ru species, and the reduction temperature of Ru species in the tube is lower than that outside the tube by 20oC in HSC2 atmosphere. The electron interaction between metal and carbon nanotubes, the space limitation of the nanotubes and the enrichment of the nanotubes may be the reasons for the difference in the distribution of the products.
【作者单位】：中国科学院上海高等研究院;中国科学院大连化学物理研究所催化基础国家重点实验室;中国科学院大学;上海科技大学;
【基金】：supported by the National Natural Science Foundation of China (21621063,21425312)~~
【分类号】：O621.251

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