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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.
Due to their unique electronic structure and properties, carbon nanotubes have drawn much interest from researchers. In particular, its ordered nanoscale luminal structure provides a unique one-dimensional confinement for both catalyst and catalytic reactions. The confinement effect of nanotubes is mainly due to the enrichment of reactants, the size limitation of the metal nanoparticles and the modulation effect on the electronic structure due to the geometrical and electronic structures of the cavities. A series of studies have shown that the limits of the carbon nanotubes Effect on the activity of the catalyst can be modulated, but the selectivity of the product less studied, especially the diameter of less than 4 nm carbon nanotubes domain system.Therefore, in this paper, cinnamic aldehyde selective hydrogenation As a probe to study the effect of the confinement effect on the product selectivity.The Ru nanoclusters were dispersed in the tube of carbon nanotubes by vapor phase filling method using carbon nanotubes with a diameter of 1-3 nm, Carbon nanotubes confined Ru catalyst (Ru @ CNT); Carbon nanotubes were prepared by impregnation on the outer wall of the catalyst (Ru / CNT) for comparison.Cinnamic aldehyde contains conjugated C = C and C = O bonds , Because C = C bond can be lower than C = O, before Hydrogenation reaction is more likely to occur.The results show that the Ru catalyst dispersed on the outer wall of carbon nanotubes can catalyze the hydrogenation of C = C in cinnamaldehyde to obtain hydrogenated cinnamic aldehyde (HCAL); and Ru @ CNT catalyst not only can catalyze C = C plus Hydrogenated cinnamic aldehyde HCAL was also obtained, which could also catalyze hydrogenation of C═O bond to obtain cinnamyl alcohol and cinnamyl alcohol. The catalysts were characterized by high resolution transmission electron microscopy, Raman spectroscopy, temperature programmed reduction and temperature programmed desorption. The size of nanotube-bound nanocluster metal particles is about 1-2 nm, which is similar to that of the metal particles loaded on the outside of the tube. However, some metal nanoclusters still exist on the outer surface of the Ru @ CNT catalyst, which may be One of the reasons for the hydrogenation of C = C bond on Ru @ CNT catalyst is that the unique limiting effect of carbon nanotubes promotes the reduction of Ru species, and the reduction temperature of Ru species in the tube is 20oC lower than that of the tube under H_2 atmosphere. The electronic interaction between the inner and outer walls of the carbon nanotubes, the spatial confinement of the nanotube cavities and the luminal enrichment may be responsible for the differences in product distribution.