Low-temperature growth of carbon nanotubes from the catalytic decomposition of carbon tetrachloride

Multiwall carbon nanotubes (MWNTs) were synthesized via the decomposition of CCl4 in supercritical CO2 at 175 degrees C and 27.6 MPa using an iron-encapsulated dendrimer as a growth catalyst. The average diameter of resultant nanotubes was 20-25 nm, obtained after a 24-h reaction time. Our conditions represent the first application for CX4 precursors, as well as the lowest-reported temperature regime for carbon nanotube growth, allowing the use of other temperature-sensitive catalytic substrates.     

CVD synthesis of spiral carbon nanotubes over asymmetric catalytic particles

The influence of asymmetric catalytic particles prepared by various methods was investigated on the growth of spiral carbon nanotubes using the CVD method. Asymmetric particles were prepared by either milling or crystallization from oversaturated solution onto the surface of catalyst support or catalyst impregnation at pH 8–9. As-prepared catalysts were tested in the decomposition of acetylene. Carbon deposit, thus carbon nanotubes and spirals were observed by transmission electron microscopy the activity was characterized by carbon yield.     

Combinatorial synthesis of carbon nanotubes by the catalytic chemical vapor deposition method

Summary Bimetallic (Fe-Co) catalyst samples prepared from different precursors over various supports were tested in carbon nanotube (CNT) production. In order to quicken the evaluation of the performance of the catalysts a combinatorial arrangement was used.</o:p>     

High-density growth of carbon nanotubes with catalytic sites activated on nickel substrate

We describe the growth of carbon nanotubes (CNTs) from catalytic nanoparticles formed on a nickel surface. For the growth of CNTs, a chemical vapor deposition (CVD) furnace was set up and ethanol was used as carbon source. Observation of SEM images shows that CNTs grew densely on the nickel surface and that nanoparticles play a key role in the growth of the CNTs. XRD and Raman analyses reveal that the obtained products have graphitic pattern of multi-walled carbon nanotubes (MWCNTs). Also HRTEM images confirm clearly that the product was a MWCNT and their diameter was in the range of 20–50 nm.     

Low-temperature single-wall carbon nanotubes synthesis: feedstock decomposition limited growth

We report on the lowest temperature of SWCNT growth using endothermic decomposition of CH4 gas on a specially activated alumina-supported Fe:Mo catalyst. However, the observed lowest growth temperature (560 degrees C) is higher than that reported previously for exothermic feedstock type. Our observation indicates that the decomposition threshold temperature of the feedstock limits the SWCNT growth. This study also suggests that, by using more active carbon feedstock or somehow facilitating its decomposition, one could enable the synthesis of SWCNT at an even lower temperature.     

溶剂热合成碳纳米管

自1991年Iijima发现碳纳米管以来,碳纳米管因其独特的结构和物理化学性质而成为人们的研究热点。     

Supramolecular catalysts for the gas-phase synthesis of single-walled carbon nanotubes

Reversed micelles containing metallic ions have been used as precursors of novel catalysts for the gas-phase synthesis of single-walled carbon nanotubes (SWNTs). This technique possesses the following advantages: (i) excellent solubility in organic solvents, which are used as reactants and (ii) facile preparation of multicomponent catalysts enabling systematic screening of catalyst compositions for the synthesis of SWNTs. In this study, we report the results of the screening study on the catalytic behavior of Fe-Mo binary catalysts during the synthesis of SWNTs. The results suggested that the catalytic ability was closely related to the strain of the crystal structure of Fe-Mo catalysts formed in the reaction and/or the phase transition caused by dissolution of the Mo atoms. The addition of lithium to the Fe-Mo binary catalysts has revealed an increase in the yield of SWNTs.     

Role of surface defects of carbon nanotubes on catalytic performance of barium promoted ruthenium catalyst for ammonia synthesis

Carbon nanotubes(CNTs) with abundant surface defects are prepared by a liquid oxidation and thermal annealing method. The defective CNTs-D supported Ba–Ru/CNTs-D catalysts exhibit superior catalytic performance in ammonia synthesis with a TOF be increased up to 0.30 s-1, which is 2.5 times of oxidized CNTs-O supported Ba–Ru/CNTs-O catalysts and 5 times of the Ba–Ru/CNTs. The characterizations by CO chemisorption, transmission electron microscope, Raman, and X-ray photoelectron spectroscopy revealed that the uniformly well dispersed Ru NPs can be stabilized on the defective sites of CNTs-D. The great improvement of the catalytic performance and stability of the Ba–Ru/CNTs-D is contributed to the strong interaction between Ru NPs and surface defect of the CNTs.     

The synthesis of few-walled carbon nanotubes by the catalytic pyrolysis of methane and the kinetics of their accumulation

The kinetic dependences of the accumulation of carbon during pyrolysis of CH₄ mixed with H₂ on an Mo-Co/MgO catalyst with the atomic ratio Mo: Co: Mg = 3: 1: 76 at atmospheric pressure, temperature 900°C, and various CH₄ and H₂ partial pressures were determined by direct thermogravimetric measurements in combination with electron microscopic examination. The main solid pyrolysis products were found to be carbon nanotubes with two to five walls. The outside diameter of nanotubes changed from ～3 to 9 nm. A kinetic model of the accumulation of carbon was suggested. The model took into account the formation of two products, nanotubes and carbon deposited on their surface, process reversibility, and catalyst deactivation by nanotubes formed.     

Doping effects of manganese on the catalytic performance and structure of NiMgO catalysts for controllabe synthesis of multi-walled carbon nanotubes

Doping effects of manganese （Mn） on catalytic performance and structure evolution of NiMgO catalysts for synthesis of multi-walled carbon nanotubes （MWCNTs） from methane were investigated for the first time. Addition of Mn in NiMgO catalyst can greatly improve the MWCNTs yield. Mno.2NiMgO catalyst among the tested ones gives the highest MWCNTs yield as 2244%, which is two times higher than that of the catalyst without Mn. The structure evolution, reduction behaviors and surface chemical properties of MnNiMgO catalysts with various Mn contents were studied in detail. It was found that the stable solid solution of NiMgO2 formed in NiMgO catalyst was disturbed by the addition of Mn. Instead, another solid solution of MnMg608 is formed. More amount of Ni can be reduced and dispersed on the catalyst surface to be acted as active sites. Importantly, the changes of Ni content on the surface are correlated with the Ni particle size and the outer diameter of MWCNTs, suggesting the controllable synthesis of MWCNTs over MnNiMgO catalysts.     

Formation and growth mechanism of dissimilar coiled carbon nanotubes by reduced-pressure catalytic chemical vapor deposition

Dissimilar coiled carbon nanotubes were prepared by catalytic chemical vapor deposition (CCVD) on finely divided Co nanoparticles supported on silica gel under reduced pressure and at lower gas flow rates. The morphology of the regular coiled carbon nanotubes were examined by TEM, while the polygonization characteristics of the helix were examined by SAED. Observations were made on other forms of irregular coils with various shapes by TEM. On the basis of the heptagon-pentagon construction theory, we proposed a helix formation mechanism, which involves a carbon core formation centering on a catalytic particle followed by carbon helices growth controlled by kinetics.     

A reevaluation of the correlation between the synthesis parameters and structure and properties of nitrogen-doped carbon nanotubes

Nitrogen-doped carbon nanotubes(NCNTs) were synthesized by chemical vapor deposition using cobaltbased oxides as catalyst and ethylenediamine(EDA) as carbon/nitrogen precursor. The influence of growth time,EDA concentration and growth temperature on the morphology,yield,composition,graphitization and oxidation resistance of the NCNTs was systematically investigated by using Raman spectroscopy,temperature-programmed oxidation and other techniques. The NCNT growth from ethylenediamine with a high N/C ratio involves several processes including mainly(1) catalytic growth of NCNTs,(2) homogeneous gas-phase decomposition of EDA,(3) non-catalytic deposition of pyrolytic carbon/nitrogen species and(4)surface etching of amorphous carbon or carbon at defect sites through gasification. At a later growth stage the etching process appears to be dominating,leading to the thinning of nanotubes and the decrease of yield.Moreover,the surface etching through carbon gasification strongly influences the structure and degree of graphitization of NCNTs.     

High-yield synthesis of single-wall carbon nanotubes on MCM41 using catalytic chemical vapor deposition of acetylene

High-quality single-wall carbon nanotubes (SWNTs) with narrow diameter distribution have been grown on Fe/Co-loaded MCM41 by using acetylene as the carbon source within a short reaction period, typically 10 min or less. The optimum temperature for SWNTs synthesis is 850 degrees C. Longer reaction time (i.e., 30 min) favors the formation of multiwall carbon nanotubes (MWNTs) and graphitic carbon. When the reaction time is reduced to less than 10 min, formation of MWNTs and graphitic carbon is greatly suppressed, and high-quality SWNTs dominates the yield. The surface of the as-grown SWNTs is found to be free from amorphous carbon, as observed from high-resolution transmission electron microscope (HRTEM) analysis. Raman spectral data show a G/D ratio above 10, indicating that the as-grown SWNTs have very few defects. Furthermore, radial breathing mode (RBM) analysis reveals that the diameter distribution of the current SWNTs is narrow and ranges from 0.64 to 1.36 nm.     

Influence of a Fe/activated carbon catalyst and reaction parameters on methane decomposition during the synthesis of carbon nanotubes

In our experimental work on carbon nanotubes synthesis, the influence of pre-treatment and reaction temperature conditions over Fe catalyst loaded on low-cost activated carbon (AC) in the catalytic chemical vapor deposition of methane was studied. Catalyst with the metal concentration of 5 mass % calcined at 350°C and reduced at 450°C was effective in CH₄ decomposition giving 98 % conversions. TEM images showed that thin multi-walled carbon nanotubes (MWNTs) with the average internal diameter of ∼ 8 nm and the wall thickness of ∼ 2.5 nm were obtained over unreduced Fe/AC catalyst at the reaction temperature of 850°C. On the other hand, broader filamentous nanostructures with the diameter of ∼ 22 nm and the wall thickness of ∼ 3.72 nm were observed over reduced catalyst.     

全氟磺酸功能化碳纳米管的制备及其催化性能

采用全氟磺酸-全氟乙烯共聚物的液相沉积方法制备了全氟磺酸功能化碳纳米管催化剂,利用N2吸附、扫描电子显微镜、透射电子显微镜、傅里叶变换红外光谱以及酸碱滴定等方法对材料的结构和酸性进行了表征,考察了温度和溶剂对催化剂稳定性的影响.结果表明,催化剂在极性和非极性溶液中均十分稳定,并且具有良好的热稳定性,使用温度可达300°C.该催化剂在对苯二酚与叔丁醇的烷基化反应中表现出优异的催化性能,其催化活性与稳定性均高于聚苯乙烯磺酸功能化的碳纳米管催化剂.     

Decorating catalytic palladium nanoparticles on carbon nanotubes in supercritical carbon dioxide

Hydrogen reduction of a Pd(II)-beta-diketone precursor in supercritical carbon dioxide produces palladium nanoparticles on multi-walled carbon nanotubes that exhibit promising catalytic properties for hydrogenation of olefins in carbon dioxide as well as electro-reduction of oxygen in fuel cell applications.     

Tandem sequential catalytic enantioselective synthesis of highly-functionalised tetrahydroindolizine derivatives

An isothiourea-catalysed enantioselective synthesis of novel tetrahydroindolizine derivatives is reported through a one-pot tandem sequential process. The application of 2-(pyrrol-1-yl)acetic acid in combination with either a trifluoromethyl enone or an α-keto-β,γ-unsaturated ester in an enantioselective Michael addition–lactonisation process, followed by in situ ring-opening and cyclisation, led to a range of 24 tetrahydroindolizine derivatives containing three stereocentres in up to >95 : 5 dr and >99 : 1 er.

The isothiourea-catalysed enantioselective synthesis of tetrahydroindolizine derivatives containing three stereocentres is reported through a one-pot tandem sequential process.     

Gram-scale CCVD synthesis of double-walled carbon nanotubes

Synthesis of clean double-walled carbon nanotubes by a catalytic chemical vapour deposition (CCVD) method is reported; the catalyst is a Mg(1 - x)Co(x)O solid solution containing additions of Mo oxide; this MgO-based catalyst can be easily removed, leading to gram-scale amounts of clean carbon nanotubes, 77% of which are double-walled carbon nanotubes.