Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter

We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.     

多壁碳纳米管的制备及改性处理

用自制的镍 硅二元气凝胶作催化剂,合成了多壁碳纳米管.甲烷在680℃催化裂解120min,再升温至800℃继续裂解20min,得到多壁碳纳米管.TEM、HRTEM和Raman光谱分析表明,所得多壁碳纳米管与高定向石墨具有相似的层状结构,其管径分布均匀,约15～30nm左右,长径比大,管端封闭,并含有金属催化剂粒子;采用不同方法改性处理,发现经过稀硝酸浸泡和空气氧化处理后,能去除碳管中金属催化剂,同时碳纳米管管长变短,端帽开口,能有效利用内表面,比表面积增大.     

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.     

AAO模板法生长碳纳米管阵列及形成机理研究

采用阳极刻蚀法制备得到多孔氧化铝模板(AAO)，通过在二茂铁苯溶液中浸润而后热解的方法，得到内壁附着纳米铁颗粒的AAO模板。用化学气相沉积(CVD)法在AAO模板孔内生长出两端开口的碳纳米管(CNTs)阵列。仅用盐酸浸泡就可除去CNTs表面上的催化剂颗粒，得到高纯的CNTs阵列。高分辨透射电镜(HRTEM)和拉曼图谱(Raman)表明CNTs具有很低的石墨化结构。通过对CNTs形貌和形成过程的剖析，认为AAO模板孔道的导向作用以及模板孔内壁催化剂铁颗粒大小分布不均是形成低石墨化碳纳米管的主要原因。     

Carbon nanotubes as a support for Pt-and Pt-Ru-catalysts of reactions proceeding in fuel cells

Comparative study of two types of single-wall carbon nanotubes and standard carbon black Vulcan XC-72 as supports for catalysts of reactions proceeding in fuel cells is carried out. The nanotubes were prepared by arc method; they differed in the degree of their purifying from amorphous carbon and metal impurities. The structure and hydrophobic-hydrophilic properties of these carbon supports are studied by etalon porosimetry. The effect of the supports’ specific surface area on the deposited catalyst particles size and specific surface area is studied. The catalysts (Pt-Ru and Pt) were deposited from aqueous solutions of their salts. Platinum was also deposited by thermal decomposition of ethoxy clusters. It is shown that in methanol oxidation reaction at the Pt-Ru catalysts the current values per unit true surface area do not depend on the support nature, provided the catalyst loading is equal and the particle size is similar. When oxygen is reduced at platinum deposited onto purified nanotubes and the carbon black Vulcan XC-72, specific kinetic currents also are close to each other. It is shown that the degree of nanotubes purification and their structure affect the kinetics of this reaction significantly.     

过渡金属氧化物和金属负载型沸石催化剂上合成 纳米碳管及其表征

采用气相催化沉积法催化合成纳米碳管,比较了不同金属氧化物和金属负载型沸石催化剂以及不同分子筛载体对合成纳米碳管的影响,并用TEM,XRD表征其形貌和结晶度,用DTA-TG考察了纳米碳管的热和稳定性。实验结果表明纳米碳管的形成除了与金属种类有关外,还直接与催化剂的颗粒大小和分散状态有关。粒径在20nm左右的不规则形状的纳米粒子是形成纳米碳管的活性组分,非负载和负载型的催化剂均表明活性组分的粒径与纳米碳管的管径有一定的对应关系。化学提纯后能得到高纯度的纳米碳管;其管壁具有较好的石墨化结构,在空气中的热稳定性大于400℃,而在氮气中能维持到1200℃以上。     

Preparation and photocatalytic behavior of TiO2-carbon nanotube hybrid catalyst for acridine dye decomposition

A new kind of hybrid catalyst, TiO₂-carbon nanotubes, was prepared via sol-gel method for the first time. Its photocatalytic activity in the photodegradation of acridine dye aqueous solution at low concentration was tested. There was no measurable effect on the formation of crystalline phase of TiO₂ catalyst with the addition of 10 wt.% carbon nanotubes to TiO₂ samples. AFM photograph of TiO₂-carbon nanotubes sintered at 300°C showed that the carbon nanotubes were enwrapped by TiO₂, which greatly increased the adsorbing ability of the catalyst and was in favor of photocatalytic reaction. Compared with naked TiO₂ powder the hybrid catalyst prepared in this way showed high efficiency in the photodecomposition of acridine dye.     

Constrained iron catalysts for single-walled carbon nanotube growth

The diameter of single walled carbon nanotubes (SWNTs) determines the electronic properties of the nanotube. The diameter of carbon nanotubes is dictated by the diameter of the catalyst particle. Here we describe the use of iron nanoparticles synthesized within the Dps protein cage as catalysts for the growth of single-walled carbon nanotubes. The discrete iron particles synthesized within the Dps protein cages when used as catalyst particles gives rise to single-walled carbon nanotubes with a limited diameter distribution.     

气凝胶催化剂上甲烷裂解制备的碳纳米管结构特征

采用XRD、TGA、SEM、TEM、 Raman光谱等多种表征手段,考察了Al2O3气凝胶催化剂上甲烷裂解生长的碳纳米管的结构特征.制得的碳纳米管形态单一,为管径均匀、管壁光滑的中空纳米管,平均直径在10～20 nm.碳纳米管的比表面积较大,具有较强的抗氧化能力,其结构的长程有序度较石墨低.由碳纳米管的Raman光谱分析可知,碳纳米管存在碳层缺陷和无定形碳.当反应温度升高或甲烷浓度下降时,碳纳米管石墨化程度逐渐提高.     

La~2NiO~4催化制备纳米碳管

制备了四方结构复合氧化物La~2NiO~4,并以其为催化剂前体,甲烷和一氧化碳为碳,合成出大量高纯度的纳米碳管。XRD结果表明La~2NiO~4经还原后,在La~2O~3的隔离作用下Ni晶粒实现纳米级均匀分散。利用TEM,HRTEM,SEM,XRD,Raman等手段对所制备的纳米碳管进行了观察和表征。所制备的纳米碳管管径均匀、石墨化程度较高,该法制备纳米碳管工艺简单、产量较高,产品易于纯化。     

碳助剂对完全液相法制备的 Cu-Zn-Al 催化剂性能的影响

 采用完全液相法制备了 Cu-Zn-Al 催化剂, 研究了碳纳米管和碳微球的加入对该催化剂 CO 加氢合成低碳醇反应性能的影响, 并用 X 射线粉末衍射、氮气吸附、氢气程序升温还原和氨气程序升温脱附-质谱等方法对催化剂进行了表征. 结果表明, 用完全液相法制备的 Cu-Zn-Al 甲醇合成催化剂具有一定的合成低碳醇和低碳烃的能力, 这种能力归结于较大 Cu0 晶粒的产生. 一定量碳微球的加入可大大减小 Cu0 晶粒度, 从而大幅度提高甲醇选择性.     

Preparation of Carbon Nanotubes from Methane on Ni/Cu/Al Catalyst

1. Introduction With the discovery of carbon nanotubes, much attention [1-3] now has been paid to their potential application in various fields, due to their many attrac- tive physical and chemical properties. They are also being used as an important material. For instance, the large cavities of carbon nanotubes can be used as an encouraging microscopic catalytic reactor [4- 5], capable of tunnel selecting molecules in different sizes. So it is important to synthesize carbon nan- otubes with t…     

Preparation of Carbon Nanotubes from Methane on Ni/Cu/A1 Catalyst

A series of Ni/Cu/Al catalyst samples were prepared by the co-precipitation method. Carbon nanotubes with large inner diameters are successfully synthesized from methane on Ni/Cu/Al catalyst by adding sodium carbonate. The effects of the copper content and amounts of sodium carbonate on the morphology and microstructures of carbon nanotubes were investigated by CO adsorption and TEM technique. The experimental results showed that copper can influence both the catalytic activity and catalyst life. Best result was obtained when the copper content was 15％. Addition of sodium carbonate favors the formation of carbon nanotubes with large inner diameters. The growth mechanism of carbon nanotubes with large inner diameter is discussed.     

Iron silicide root formation in carbon nanotubes grown by microwave PECVD

Aligned carbon nanotubes have been grown using microwave plasma enhanced chemical vapor deposition (PECVD). The carbon nanotubes are nucleated from iron catalyst particles which, during growth, remain adherent to the silicon substrates. By analysis with high-resolution electron microscopy, we observe iron silicide roots penetrating into the silicon substrate at the interface of the catalyst particles and the substrate, thus providing strong adhesion of the carbon nanotubes onto the substrate. The iron silicide roots assist in the attachment of the catalyst particles to the substrate and play a role in the evolution of the catalyst particle morphology and resulting base growth mode. Carbon nanotubes grown by microwave PECVD could exhibit superior electrical and thermal transport properties over other PECVD processes, so an understanding of the growth mechanism is important for utilization in device applications.     

碳纳米管担载CuCoCe催化剂催化合成气制低碳醇的性能

以碳纳米管为载体,采用等体积浸渍法制备了一系列Cu Co Ce催化剂,考察了碳纳米管长度及羧基官能团对该系列催化剂催化合成气制低碳醇反应性能的影响;采用X射线衍射(XRD)、氮气吸附-脱附、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等手段对催化剂进行了结构和性能表征.实验结果表明,以含有羧基官能团的、长度为0.5~2μm的碳纳米管为载体时,催化剂的低碳醇时空收率最高,达到783.72mg·gcat-1·h-1,醇产物中C2+醇选择性达到82.71%.研究结果表明,短纳米管有利于活性金属进入碳纳米管内部,并促使活性组分分散均匀,这对CO转化率和低碳醇时空收率的提高有显著作用;碳纳米管上羧基官能团的存在促进了金属与金属、金属与载体之间的相互作用,从而使醇产物中C2+醇选择性明显提高.     

在Pt/CNTs催化层中预混-溶解La2O3颗粒来构筑孔结构促进甲醇电氧化

为认识孔隙度增加对甲醇电氧化的影响, 将熔盐法制备的La2O3颗粒与Pt/CNTs(碳纳米管)预混合然后用HClO4溶掉La2O3颗粒, 从而增加了Pt/CNTs催化层的孔隙度. 扫描电子显微镜(SEM)观察表明, 该处理可以形成孔结构. 用循环伏安和计时电流实验考察了孔隙度增加对甲醇电氧化的影响, 结果表明甲醇电氧化电流可增加57%. 分析认为, 电流增加的原因是由于多孔催化层中甲醇更易于到达Pt催化剂表面进行电氧化. 该研究表明, 通过在催化层中预混-溶解La2O3来增加孔隙是一种改善催化层性能的有效方法.     

在Pt/CNTs催化层中预混-溶解La2O3颗粒来构筑孔结构促进甲醇电氧化

为认识孔隙度增加对甲醇电氧化的影响,将熔盐法制备的La2O3颗粒与Pt/CNTs(碳纳米管)预混合然后用HClO4溶掉La2O3颗粒,从而增加了Pt/CNTs催化层的孔隙度.扫描电子显微镜(SEM)观察表明,该处理可以形成孔结构.用循环伏安和计时电流实验考察了孔隙度增加对甲醇电氧化的影响,结果表明甲醇电氧化电流可增加57%.分析认为,电流增加的原因是由于多孔催化层中甲醇更易于到达Pt催化剂表面进行电氧化.该研究表明,通过在催化层中预混-溶解La2O3来增加孔隙是一种改善催化层性能的有效方法.     

不同活性炭负载的镍基催化剂上废塑料裂解制碳纳米管性能

以椰壳炭、竹炭和木炭三种活性炭为载体,采用浸渍法制备炭负载金属镍的催化剂,考察其在废塑料裂解制备碳纳米管过程中的催化反应性能;采用X射线衍射、扫描电镜、透射电镜、拉曼光谱仪、同步热分析仪、比表面积分析仪等手段分析了催化剂和产物碳纳米管的形貌和结构。结果表明,椰壳活性炭为载体制备的镍基催化剂上碳纳米管产量最高、石墨化程度最好。以椰壳活性炭为载体制备的镍基催化剂为例,研究了反应温度和镍负载量对其催化性能的影响。     

Fischer–Tropsch synthesis over CNT-supported cobalt catalyst: effect of magnetic field

In the present work, the cobalt catalysts supported on carbon nanotubes (CNTs) were prepared by impregnation method in the presence and absence of magnetic field. The prepared catalysts were employed to yield higher hydrocarbons via Fischer–Tropsch synthesis. It is explored that using magnetized water can effectively change the catalyst geometry in impregnation catalyst preparation method. For the preparation of different sizes of cobalt particles on the CNTs support, the physical properties of solvent (water) in impregnation process were changed using the magnetizing process. The results showed that the average particle sizes of impregnated cobalt nanoparticles were decreased by using magnetized water in impregnation step. In addition, in the magnetized treated cobalt catalyst, the cobalt particles mostly dispersed outside the tubes because the capillary forces decreased by reducing water surface tension. Furthermore, the experimental results showed that the probability of chain growth (α) and selectivity to heavier hydrocarbons increased in magnetized water treatment catalysts.     

多壁纳米碳管空气电极的交流阻抗研究

研究了多壁纳米碳管、活性炭和石墨等空气电极的交流阻抗特性.结果表明,纳米碳管空气电极的阻抗谱由两个半圆组成,高频区半圆对应欧姆极化阻抗,低频区半圆对应电化学极化阻抗.催化剂Pt以纳米颗粒的形式沉积在碳管的外表面,明显减小了电极的欧姆阻抗和电化学极化阻抗,提高了氧还原反应的电催化活性.活性炭电极除存在电化学阻抗外,还存在薄液膜扩散阻抗(Nernst扩散),石墨电极形成的薄液膜反应区域较小,电极反应呈Warburg扩散阻抗特征,相应的电催化活性较低.采用交流阻抗等效电路分析方法,对拟合的动力学数据进行了解释.