Ligand-free catalytic system for the synthesis of diarylethers over Cu2O/Cu-CNTs as heterogeneous reusable catalyst

Various substituted diarylether derivatives were prepared by using heterogeneous reusable Cu₂O- and Cu-coated carbon nanotubes (Cu₂O/Cu-CNTs) as catalyst under ligand-free conditions, which provided good to excellent yields. The catalyst was characterized by TEM, XRD, and AAS analysis. The effects of solvent, base, and amount of catalyst for the O-arylation were investigated. The catalyst could be recovered by simple filtration from the reaction mixture without further treatment and reused several times with consistent catalytic activity. In addition, CNTs could also be recovered from the used Cu₂O/Cu-CNTs by a simple acid treatment.     

A parametric study of methane decomposition into carbon nanotubes over 8Co-2Mo/Al2O3 catalyst

The effects of reaction temperature, partial pressure of methane, catalyst weight and gas hourly space velocity (GHSV) on methane decomposition were reported. The decomposition reaction was performed in a vertical fixed-bed reactor over 8Co-2Mo/Al 2 O 3 catalyst. The experimental results show that these four process parameters studied had vital effects on carbon yield. As revealed by the electron microscopy and Raman spectroscopy analyses, the reaction temperature and GHSV governed the average diameter, the diameter distribution and the degree of graphitization of the synthesized carbon nanotubes (CNTs). Also, an evidence is presented to show that higher temperatures and higher GHSV favored the formation of better-graphitized CNTs with larger diameters.     

Efficient Synthesis of p-Hydroxyphenyl Ethanol from Hydrogenation of Methyl p-Hydroxyphenylacetate with CNTs-promoted Cu-Zr Catalyst

Hydrogenation of methyl p-hydroxyphenylacetate has been used for the synthesis of p-hydroxyphenyl ethanol. The reaction was catalyzed by Cu_iZr_j-x%(mass fraction) carbon nanotubes(CNTs) catalysts. Incorporation of a minor amount of CNTs into Cu_iZr_j oxide can visibly increase the catalytic activity for the synthesis of p-hydroxyphenyl ethanol. The yield of p-hydroxyphenyl ethanol reaches 94.2% over a co-precipitated catalyst of Cu₃Zr₁ oxide with 11.0%CNTs. Its catalytic activity shows no obvious decrease after three cycles. This is much better than the CNT-free co-precipitated catalyst with a good yield of 81.1%, Cu₃Zr₁-0%CNTs.     

甲烷部分氧化气氛制备碳纳米管

碳纳米管是由碳六元环构成的类石墨平面卷曲而成的纳米级中空管,其中每个碳原子通过sp2杂化与周围3个碳原子发生完全键合,管的直径在几个纳米到几十个纳米之间,而轴向长度却可达几十微米甚至更长,故被称为准一维分子纳米材料.由于这种特殊结构,碳纳米管具有许多奇异的物理化学性能,如独特的导电性、极高的机械强度、润滑性和吸附能力等.自发现碳纳米管以来[1],人们开展了多种方法进行制备研究,如电弧放电(Arcdischarge)[2]、激光烧蚀(Laserablation)[3]、碳氢化合物催化分解(Catalyticdecompositionofhydrocarbons)[4]和化学气相沉积(Chem…     

催化剂对纳米聚团床法制备的纳米碳材料形貌的影响

 在纳米聚团床中用催化化学气相沉积法批量制备了碳纳米管，研\r\n究了过渡金属催化剂对碳纳米管形貌和产量的影响．实验结果表明，含\r\n铁催化剂的活性较低，产率较低，但产品质量较好；含镍催化剂的活性\r\n较高，产率较高，但产品质量较差；在钴催化剂作用下发现了一种新型\r\n的针状纳米碳材料．用含载体较少的铁催化剂可以得到纯度较高且微观\r\n结构较好的碳纳米管，但产率较低；不含任何载体的纯镍催化剂则不能\r\n得到碳纳米管．适宜的催化剂组成、催化剂活性点的均匀分布和裂解速\r\n度的控制等构成了纳米聚团床大批量制备碳纳米管技术的关键．     

水促进Co/Mo/Al2O3催化剂上碳纳米管的生长

对水促进Co/Mo/Al2O3催化剂裂解乙烯生长碳纳米管(CNTs)的研究发现,通入体积分数(φ)为0.6％的水蒸汽在1h内可将CNTs的生长倍率从3.7 g·g-1提高至70 g·g-1.水的作用在于恢复被无定形碳包覆的催化剂颗粒的活性,水的加入量由于其积碳(促进同体碳生成)和消碳(去除固体碳)的竞争作用而存在最佳值.不同反应时间下乙烯的转化率与有效催化剂含量的分析表明,在CNTs生长后期,水的催化促进作用减弱.将催化剂的相对活性与CNT聚团的相对密度关联发现,反应后期的CNTs主要在聚团内部缠绕生长,催化剂被包覆失活.拉曼测试与差热热重分析表明,生长阻力导致所得CNTs缺陷增多,CNT聚团密度变化与CNT缺陷间存在对应关系.聚团内外CNTs的生长阻力不同,生长倍率不同,导致产品纯度不均匀.     

Effect of processing temperature on growing bamboo-like carbon nanotubes by chemical vapor deposition

The present article demonstrates a simple, eco-friendly route for the fabrication of carbon nanotubes (CNTs) with different morphologies, including the fascinating bamboo-like structures without complex catalyst/support preparation procedures. A thermal chemical vapor deposition (CVD) technique that utilized natural pozzolan supports and a solid carbon source, that is, a mixture of camphor and ferrocene in a weight ratio of 20:1, was carried out at different temperatures where the ferrocene played also the role of catalyst. The pozzolan chemical composition and mineral identification were determined by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The morphology of the fabricated CNTs was studied via scanning and transmission electron microscopies (SEM and TEM). It was revealed that both conventional tubular and bamboo-like nanotubes grow at 750 °C while the bamboo-like morphology prevails at 850 °C. The better nanostructure uniformity at higher deposition temperature was accompanied by an improved nanotube graphitization degree that was verified by Raman spectroscopy. Yet, the reduction of the CNTs production yield was recorded by thermogravimetric analysis (TGA). The experimental data are interpreted and discussed as an interplay between the CNTs processing temperature, morphology and growth mechanism. Thus, the growth of either tubular or bamboo-like nanostructures is suggested to be ruled by the competitive surface and bulk diffusions of carbon onto and into the catalyst surface. The growth depends on the size of catalyst nanoparticles sintered at different temperatures. The favorable role of the pozzolan supporting materials in the formation of bamboo-like tubes is emphasized.     

纳米CaCO3负载过渡金属CVD法制备多壁碳纳米管的研究

以纳米碳酸钙粉体为载体,用浸渍法制备了可用于化学气相沉积(CVD)法制备碳纳米管的高产率催化剂.应用FESEM,HRTEM,TEM,XRD和激光拉曼谱对产物进行了表征.结果表明,由于纳米碳酸钙具有较大的比表面积,可高密度地承载催化剂活性组分.在碳纳米管生长初期,处于缓慢分解状态的纳米碳酸钙才能有效地起到载体作用,且反应温度为700～750℃时,碳纳米管的产率较高.Fe-Co双金属催化剂在700℃,催化生长60min后,可增重10倍,而且产物中无定形碳含量极少.纳米碳酸钙载体易于提纯,用质量分数为30%的硝酸超声提纯粗产品1h,可使纯度提高到97%,且不破坏碳纳米管结构.     

X-ray fluorescence as a method of monitoring metal catalyst content during the purification of carbon nanotubes

There have been several studies that suggest that catalyst metals in carbon nanotubes (CNTs) may pose a health threat. As there are many potential applications of CNTs in medicine, it is important to be able to quantitatively determine the amount of metal catalyst contained in a CNT sample. The relative catalyst content of carbon nanotube samples synthesized via arc-discharge has been determined at various stages of the purification process using X-ray fluorescence (XRF) analysis. Purification was achieved by immersing samples in heated nitric acid. The intensities of the nickel K_α X-rays were studied to determine the relative catalyst content in the samples. Scanning electron microscopy (SEM) images of purified nanotubes have been compared to the images of a sample that has been irradiated by 0-15 keV bremsstrahlung in order to determine if the XRF analysis of the nanotubes is in any way destructive. No obvious structural defects were observed as the result of irradiation.     

有机膦酸盐衍生的氮掺杂的磷酸钴/碳纳米管杂化材料作为高效氧还原电催化剂（英文）

随着环境污染和能源危机的日益严重,探索高效的非贵金属氧还原电催化剂来替代商业Pt/C迫在眉睫.其中,报道比较多的是具有钴基活性物种和氮掺杂碳的复合材料例如Co-Nx-C, Co3O4/GO, Co-N/CNT等,该复合材料具有高导电性、良好的稳定性和优异的催化活性.与其他钴基催化剂相比,磷酸钴由于其成本低廉,对环境友好,多功能的优良特性,已被广泛应用于催化、吸附、分离及储能等领域,在电催化方面也有极大的应用潜力.研究表明,磷酸基团不仅可以充当质子受体,也会诱导局部钴原子的几何结构发生扭曲,从而有利于水分子的吸附并促进析氧反应的发生.此外,磷酸钴也被证实具有一定的氧还原活性.尽管磷酸钴电催化剂的研究已经取得了一定进展,磷酸根有利于质子传输,但是其导电性很差,不利于电荷的转移和传输,使得其电催化活性不高.将磷酸钴和导电碳材料复合是解决问题的有效方法.而且,磷酸钴在碱性溶液中并不稳定,极大限制了其在电催化氧还原中的应用.金属有机膦酸盐是一类包含金属离子和有机膦酸配体的杂化材料,通过简单的焙烧便可以很容易地得到金属无机磷酸盐,并且在焙烧过程中氮掺杂的碳也会原位产生,并包覆在磷酸钴的表面,使得其导电性和催化活性大大提高.为此,本研究组制备了有机膦酸钴衍生的磷酸钴和氮磷掺杂的石墨烯的复合材料并用于电催化氧还原和析氧反应,所得到的材料导电性和稳定性良好,然而,该催化剂的表观活性与商业Pt/C相比仍有较大差距,且使用有机膦酸钴作为前驱体对活性的影响也不甚清楚.因此,本文采用含氮的有机膦酸配体乙二胺四亚甲基膦酸钠(EDTMPS)为磷源制备了氮掺杂的磷酸钴/碳纳米管杂化材料(CoPiC-N/CNT-3),其催化活性和稳定性良好,并进一步探讨了各种不同因素对电催化活性的影响.XRD和TEM结果表明,用这种方法得到的磷酸钴(CoPiC)为Co2P2O7物相,与磷酸二氢钠为磷源制备得到的CoPi相比,CoPiC的表面有石墨化碳层的存在, EDS图谱表明, Co, P, C, N均匀地掺杂到复合材料的骨架结构中.Raman光谱结果表明,石墨化碳层的存在和适量的碳纳米管的引入均可以增强复合材料的石墨化程度并提高了导电性,而氮掺杂导致其缺陷位点增多.XPS结果进一步表明,有机膦酸钴可以作为前驱体可制得氮掺杂的磷酸钴/碳纳米管杂化材料.电催化反应测试表明, CoPi C-N/CNT-3的氧还原活性与商业Pt/C相当,其遵循的是4电子的反应路径,而且抗甲醇氧化能力和稳定性均优于Pt/C.原因主要归结于以下几点:(1)磷酸钴颗粒与氧化碳纳米管的协同作用可以显著增强氧还原催化活性,引入的碳纳米管可以克服磷酸钴导电性差的缺陷;(2)磷酸钴在复合材料中分散均匀,使得可以充分利用催化剂的活性位点;(3)氮掺杂可以调变材料的电子结构,从而改善催化活性;(4)石墨化碳层的存在可以改善材料的电子导电性和稳定性,有利于电子转移并可以保护磷酸钴颗粒在催化氧还原反应过程中不被电解液腐蚀.可见,所制有机膦酸衍生的氮掺杂的磷酸钴/碳纳米管杂化材料有望替代Pt/C催化剂,并推动清洁可再生能源领域的相关研究.     

CVD Growth of Carbon Nanotubes and Nanofibers: Big Length and Constant Diameter

Summary: We report mass production of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) with relatively high length and aspect ratio. We synthesized carbon nanomaterials by chemical vapor deposition (CVD) of methane as the feeding gas on Fe/Mo nanoparticles that use alumina-aerogel support. Alumina-aerogel-supported Fe/Mo catalyst was prepared using sol-gel. Drying step performed using rotary evaporation and freeze-drying. CVD was performed using a quartz tube furnace. Samples were analyzed using scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Raman spectroscopy.     

利用无水乙醇分解制备碳纳米管

利用CVD法高温分解无水乙醇,以分子筛（合成皂石）基体上的Fe颗粒为催化剂,制备出了管壁更薄、端部为开口结构的碳纳米管.本实验制备出的碳纳米管,相对于传统CVD方法制备出的碳纳米管,在实验条件控制稳定的情况下,管壁较直、缺陷较少、管内径较大.具有这样结构的碳纳米管在储氢等方面应具备更为优良的效果,从而有着潜在的应用前景.     

催化剂对东都风化煤硝酸氧解及其产物特性的影响

对东都风化煤进行硝酸氧解，利用元素分析与红外光谱分析研究产物硝基腐植酸（NHA）的结构和性质，讨论硝酸氧解中催化剂对硝基腐植酸的产率、元素组成和官能团的影响。结果表明，浓硫酸、过氧化氢、碳纳米管负载过渡金属和固体酸催化剂都能显著提高煤氧解NHA的产率，产物C、H的质量分数和H/C原子比降低，氮的质量分数增加，E4/E6增加。固体酸与浓硫酸对提高产物氮的质量分数更明显，镀镍碳纳米管（CNTs）负载三氧化二铁、碳纳米管负载镍和浓硫酸作为催化剂得到腐植酸分子更小。催化剂存在下产物活性官能团增加更多，不同催化剂对产物有不同的影响。     

Preparation and characterization of CNTs/PE micro‐nanofibers

Multiwalled carbon nanotubes (CNTs)/polyethylene micro‐nanofibers with content ranging from 0.5 to 10 wt% of CNTs were prepared for the first time by melt extrusion of immiscible blends with cellulose acetate butyrate (CAB) and subsequent removal of CAB matrix. The morphology development of dispersed phase was studied with samples collected at different zones in a twin‐screw extruder. The morphology of the CNTs in PE was found to be in forms of both individual and agglomerations. The average diameters of CNTs/PE nanofibers increased with increasing the CNTs content. The electrical conductivity of CNTs/PE nanofibers was studied and a percolation threshold of about 4 wt% was obtained. In addition, the crystalline structures of the CNTs/PE nanofibers were analyzed, indicating a decrease in the crystallinity with the addition of CNTs. The thermal properties of composite fibrils were also modified. This paper demonstrates a good approach for the preparation of CNTs/TP nanofibers by in situ microfibrillar formation. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of CNT incorporation on PAN/PPy nanofibers synthesized by electrospinning method

In this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H₂SO₄/HNO₃/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.     

高温退火一步非破坏性纯化碳纳米管

针对催化化学气相法合成的碳纳米管含有金属、金属氧化物和碳杂质, 且缺陷较多进行了非破坏性纯化研究. 基于碳纳米管与碳杂质间结构、性质的微小差异, 1800 ℃使粗制的碳纳米管高温退火3 h, 为避免碳纳米管氧化, 高温退火过程在氩气气氛中完成. 运用扫描电镜、透射电镜观察碳纳米管的形貌和结构, 发现高温退火后, 碳纳米管的端帽大部分被打开. 能谱检测显示, 粗制的碳纳米管中的杂质(Al, Si, Ni, Cu 质量分数w分别为4.67%, 0.27%, 40.12%和1.34%)退火后被除去. 拉曼分析表明, 退火前后石墨D, G峰面积S_D, S_G分别从1314900降至474921, 767157降至566292, 退火不仅有效地去除了样品中的碳杂质, 而且使碳纳米管的缺陷得到一定程度的修复, 石墨化度随之大大提高. 研究提出了一种简单的、非破坏性的、便于规模化的纯化方法.     

助剂铬对Ni/MgO催化剂CVD法制备碳纳米管的促进作用

采用溶胶-凝胶法制备了助剂Cr改性的Ni/MgO催化剂, 用化学气相沉积(CVD)法在600 ℃下裂解甲烷生长碳纳米管, 研究了助剂Cr的引入对催化剂微结构和制备碳纳米管性能的影响. 催化剂样品用XRD, TPR和CO-TPD进行了分析, 制备的碳纳米管用TEM和XRD进行了表征. 实验结果表明, NiO和MgO之间存在着强相互作用而形成固溶体, Ni/MgO催化剂经氢气处理后其中的镍氧化物只有极少部分被还原成为镍. 助剂铬的引入明显促进了镍的还原, 使得催化剂表面的Ni活性中心数增多, 从而使催化剂的活性和性能得到了明显的改进. 在加入助剂后碳纳米管的产率明显增加, 当Cr质量分数为8%时, 碳纳米管的产量为未加助剂时产量的5倍, 碳纳米管和催化剂的质量比达到1928. 当Cr含量进一步增加时, Ni在催剂表面聚集形成大颗粒, 制备出的产品中含有大量的碳纳米纤维和无定形碳. 以8%Cr-Ni/MgO催化剂合成的碳纳米管具有比较高的产率且质量较好.     

酞菁裂解法多壁碳纳米管的制备、表征和应用

In order to investigate the catalytic activity of high temperature treated CoPc toward oxygen reduction, and find the active site of the catalyst, using cobalt (Ⅱ) phthalocyanine (CoPc) as raw material, through thermal chemical vapor deposition method at 850℃ under a current of Ar/H2, two layer well-aligned multiwalled carbon nanotubes (CNTs) were made. The diameters of the well-aligned carbon nanotubes were distributed in the range of 60～120 nm and the length was about 40 μm. The Co particle with 10 nm in diameter was encapsulated in the CNTs compartment. The products were observed by field emission scanning electron microscope (SEM), and transmission electron microscope (TEM). The well-aligned carbon nanotubes were characteriszed by Raman scattering spectrum and X-ray diffraction (XRD). The cyclic voltammetric measurement demonstrates that the CNTs have some effect to prevent the metal nanoparticle encapsulated from eroding rapidly. It is assumed that the small amount of the N element in the CNTs is very necessary for the bamboo-like morphology and the protected action for metal particles against dissolution in the acid medium. The radian of the winding wall should be affected by the amount of the N and the interaction between the N in the carbon network and the metal cluster. In addition, the CNTs greater electrochemically active surface area is a great advantage for any electrocatalytic application.     

Graphitic encapsulation of catalyst particles in carbon nanotube production

A new model is proposed for the encapsulation of catalyst metal particles by graphite layers that are obtained, for example, in low-temperature chemical vapor deposition production of carbon nanotubes (CNTs). In this model graphite layers are primarily formed from the dissolved carbon atoms in the metal-carbide particle when the particle cools. This mechanism is in good agreement with molecular dynamics simulations (which show that precipitated carbon atoms preferentially form graphite sheets instead of CNTs at low temperatures) and experimental results (e.g., encapsulated metal particles are found in low-temperature zones and CNTs in high-temperature regions of production apparatus, very small catalyst particles are generally not encapsulated, and the ratio of the number of graphitic layers to the diameter of the catalyst particle is typically 0.25 nm(-1)).     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe-MgO、Co-MgO和Ni-MgO为催化剂,CH4为碳源气,H2为还原气,在873、973和1073 K制备出碳纳米管,通过TEM和拉曼光谱表征,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响.结果表明:不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异.其中Fe-MgO催化剂制备的碳纳米管管径粗,且大小不均匀,而Ni-MgO催化剂制备的碳纳米管管径较细、较均匀.碳纳米管的产率随着裂解温度的变化而改变.Fe-MgO催化剂制备碳纳米管的产率随制备温度的升高而提高,而Ni-MgO催化剂制备碳纳米管的产率随制备温度的升高而降低.Fe-MgO催化剂制备碳纳米管,在1073K甚至更高的制备温度才能达到其最高产率.Co-MgO催化剂制备碳纳米管的产率在973 K左右产率较高,而用Ni-MgO催化剂制备碳纳米管,则在873 K甚至更低的制备温度就能达到最高产率.反应时间与碳纳米管的产率不成正比,有一最佳反应时间,如Ni-MgO催化剂的最佳反应时间为2 h.