Concentration Of Catalyst Precursor Research Articles

Highly individual single-walled carbon nanotubes synthesized by floating catalyst chemical vapor deposition for transparent conducting films

The bundle formation of single-walled carbon nanotubes (SWCNTs) has dramatically hindered their performances of transparent conducting films (TCFs). Herein, we synthesized less bundled SWCNTs by reducing the concentration of catalyst precursor in floating catalyst chemical vapor deposition. The gas-phase number concentration of SWCNTs could be reduced from 1.6×106 to 4×105 cm−3 by decreasing the catalyst precursor and thus, the bundle formation due to nanotube collisions induced by Brownian diffusion was significantly inhibited. ∼42% of SWCNTs were found to be individual with a mean tube diameter of 1.0 nm, mean length of 2.5 μm and mean bundle diameter of 2.1 nm, the corresponding SWCNT TCF exhibited a sheet resistance of 109 Ω/sq. at 90% optical transmittance. Our work provides a strategy of synthesizing highly individual SWCNTs for enhanced performance of TCFs, implying great potential in electronic applications.

Growing carbon nanotubes on continuous carbon fibers to produce composites with improved interfacial properties: A step towards commercial production and application

A scalable manufacturing process has been developed to grow carbon nanotubes (CNTs) in situ on the surface of continuous carbon fibers (CFs) and achieve their uniform distribution. The successful growth of CNTs on the fiber surfaces was proved by studying the various stages in the continuous growth process. Electrochemical anodization achieved significant modification of CFs and promoted effective coating of catalyst precursors. The average tensile strength of the CNTs/CF reinforcement was improved when the concentration of catalyst precursor was 0.05 mol/L, indicating that the damage caused by catalyst reduction was repaired in chemical vapor deposition (CVD) process. The simple measurement of growth kinetics explained the rate at different stages of CNT growth. The CNT layer improved the wettability between CFs and epoxy, and effectively inhibited expansion of interfacial cracks so that the interfacial shear strength (IFSS) of composite material reached 91.17 MPa with a significant increase of 95.43%. Significantly, this process can realize the industrialization of the preparation of composite reinforcement.

A lightweight CNWs-SiO2/3Al2O3·2SiO2 porous ceramic with excellent microwave absorption and thermal insulation properties

To obtain excellent microwave absorption and thermal insulation properties, carbon nanowires reinforced SiO2/3Al2O3·2SiO2 composite ceramics (CNWs-SiO2/3Al2O3·2SiO2) were fabricated by catalytic chemical vapor deposition (CCVD) using C2H4 as the carbon source. The content of CNWs in SiO2/3Al2O3·2SiO2 porous ceramics can be adjusted by controlling the concentration of the catalyst precursor and the CCVD time. A higher concentration of catalyst precursor and longer CCVD time are beneficial for the growth of CNWs and for improving the electromagnetic wave (EMW) absorption properties of CNWs-SiO2/3Al2O3·2SiO2. However, CNWs are harmful to impendence matching due to the strong reflection and weak absorption when the content exceeds the threshold (30 wt%) in SiO2/3Al2O3·2SiO2 porous ceramics. CNWs are also harmful to the thermal insulation properties due to their high thermal conductivity. The results show that CNWs-SiO2/3Al2O3·2SiO2 can attain good EMW absorption and thermal insulation properties if the content of CNWs is 30 wt% when the concentration of the catalyst precursor is 3 wt% and the CCVD time is 15 min. The effective absorption bandwidth (EAB) can cover from 8.2 to 12.4 GHz (the whole X-band), and the minimum reflection coefficient (RCmin) is -31 dB at 9.1 GHz. The temperature gradient is 218 °C, which can satisfy the design requirement. Thus, the dielectric and thermal insulation properties are designable for CNWs reinforced SiO2/3Al2O3·2SiO2 porous ceramics to obtain excellent EMW absorption and thermal insulation properties.

In situ growth of CNTs on carbon fiber by chemical vapor deposition

Carbon nanotubes (CNTs), as a kind of one-dimensional nanomaterial with special structure, have excellent properties in various aspects. Grafting CNTs onto carbon fiber (CF) surface to improve the mechanical properties of carbon fiber reinforced composites has been the focus at home and abroad. In this paper, chemical vapor deposition (CVD) was used to in situ grow CNTs on CF surface with carbon monoxide (CO) as carbon source and ferric nitrate (Fe (NO3)3·9H2O) as catalyst. The effect of different process conditions on the growth of CNTs were explored and the mechanism was briefly described. It is found that the oxidation treatment of CF could introduce a large number of reactive groups on the surface of CF, which was conducive to uniform dispersion of the catalyst. The morphology of CNTs were characterized by scanning electron microscopy (SEM). The results showed that the optimum growth concentration of catalyst precursor was 0.05 mol/L.

Experimental Study on Homogeneous Catalytic Upgrading of Heavy Oil

Four catalyst precursors were prepared to assess the performance on the upgrading process of heavy oil. It has been showed that viscosity of Lukeqin heavy oil was decreased significantly, which revealed a viscosity reduction ratio of up to 99.28% with a catalyst precursor concentration of 0.12 wt %, reaction temperature of 365°С and reaction time of 40 min. Analysis of the oil after upgrading showed an obviously change in the composition of hydrocarbon components. The increase of light fractions after reaction improved the properties of heavy oil which is benefit to the pipeline transportation and downstream refining. Meanwhile, the mechanism of upgrading was also investigated. This work proved that heavy oil can be effectively upgraded with the catalyst precursor of petroleum acid iron.

Friedel-Crafts Alkylation of Toluene as a Parallel Reaction in Propylene Dimerization Catalyzed by Nickel β-Diimine Complex/EASC in Homogeneous Phase

A oligomerizacao do propeno foi realizada utilizando o complexo dibromo-bis(N,N'- difenilpentano-2,4-diimina)niquel(II) como precursor catalitico combinado ao sesquicloreto de etilaluminio (Al2Et3Cl3, EASC) como co-catalisador. A 10 oC, usando o tolueno como solvente, altas frequencias de rotacao foram obtidas (ate 57000 h–1) com alta seletividade em produtos C6 (ate > 99%) e seletividade moderada em C6 linear (ate 29%). Observou-se que nas condicoes experimentais empregadas o propeno reagiu com tolueno por reacao de Friedel-Crafts. O aumento da concentracao de precursor catalitico, mantendo constante a relacao precursor/co-catalisador, teve por efeito de aumentar a selectividade para os produtos de oligomerizacao em relacao aos produtos de alquilacao por reacao de Friedel-Crafts.

Towards a ‘catalyst activity map’ regarding the nucleation and growth of single walled carbon nanotubes

Quantification using scanning electron microscopy (SEM) of single walled carbon nanotubes (SWNTs) grown per unit area using a Co-Fe (50:50) catalyst system, prepared by the incorporation of the appropriate metal salts into a Spin-On Glass substrate, at 900°C. The effects of substrate, as well as catalyst precursor concentration, were investigated. SWNT growth density is maximised with a catalyst precursor concentration of ≥2.5 mM, associated with the formation of catalyst nanoparticles of a critical size for SWNT nucleation. Samples were subjected to secondary growth, using a range of H2:CH4 ratios to determine the optimum precursor composition. It was found that nucleation and growth stages are optimal under different conditions. Optimum conditions for nucleation resulted in >10× increase in SWNT density. Optimisation is dependent on temperature and the partial pressure of reagent gas species.

Preparation of Ru–Cs catalyst and its application on hydrogen production by ammonia decomposition

Ammonia can be a hydrogen source for many applications including fuel cells. Using Ru or Cs–Ru as the catalyst, hydrogen is generated from ammonia by decomposition reaction. These catalysts are deposited on carbon powder by either chemical reduction or precipitation method in this study. Different carbon powder pre-treatment solutions and catalyst deposition conditions are evaluated. Nitric acid pre-treatment followed by precipitation at pH of 6 produces the highest catalyst loading from solution with given concentration of catalyst precursor. Hydrogen generation rate is measured at different catalyst compositions, ammonia inlet flow rates, decomposition temperatures, amount of catalyst packing, and ratio of Cs/Ru. The optimal condition for the ammonia decomposition reaction is Cs/Ru weight ratio at 3, ammonia inlet flow at 6 ml min−1, reaction temperature at 400 °C. At this condition, the ammonia conversion rate reaches 90% and hydrogen generation rate reaches 29.8 mmol/min-gcat.

Controllable growth of single-walled carbon nanotubes by ethanol-ferrocene aerosol method

Aerosol-assisted chemical vapor deposition (AACVD), a method for producing single-walled carbon nanotubes (SWCNTs) with the use of ethanol and ferrocene as the sources of carbon and a catalyst introduced into a reactor by means of an ultrasound nebulizer, is described. The influence of different parameters such as temperature, growth time, and catalyst precursor concentration on the diameter and chirality of SWCNTs is studied by optical absorption spectroscopy. The suggested technique makes the production of small-diameter SWCNTs (0.75–1.43 nm) with sufficiently stable chirality distribution close to the achiral structures.

Fabrication of ACF/CNT Composites by CVD Method

Aiming at a novel adsorption agent material, ACF/CNT composites were fabricated by growing carbon nanotubes (CNTs) on the surface of activated carbon fibers (ACFs) with chemical vapor deposition (CVD) method. The characteristics of ACF/CNT composites were investigated by SEM. The variables effects on CNTs size, uniformity and density were evaluated. Three major variables were optimized as the concentration of catalyst precursor 0.07 mol/L, pyrolysis temperature 750 and pyrolysis time 40 min respectively. The results show that CNTs are uniform distribution on the surface of ACFs and the diameter of CNTs is in the range of 30-60 nm and BET specific surface area is 65.39 m2/g. ACF/CNT composites are looked forward to be a promising materials for wastewater and flue gas treatment and hydrogen storage for proton exchange membrane fuel cells.

Electrospinning of carbon nanofiber supported Fe/Co/Ni ternary alloy nanoparticles

Polyacrylonitrile (PAN)-based carbon nanofiber supported Fe/Co/Ni ternary alloy nanoparticles were prepared by using the electrospinning technique for potential fuel cell applications. The solution was prepared by adding pre-solved catalytic precursor into PAN/DMF solution. The effect of PAN and catalyst precursor concentration on solution properties (viscosity and conductivity) and heat stabilization temperature has been investigated. Electrospun nanofibers were characterized by field emission scanning electron microscope, transmission electron microscope, energy dispersive spectrometer and X-ray diffractometer. It has been found that ternary nanoparticle size is in the range of 5–115 nm (average: 20 nm) and is a crystal alloy of Fe, Co and Ni. Also, TEM results demonstrate that in some regions metal nanoparticles tend to agglomerate into larger particles mainly due to the non-uniform distribution of nanoparticles in as-spun condition. PAN-derived carbon nanofiber mean diameter was measured as 200 nm by varying from 40 nm to 420 nm.

Large scale synthesis of vertical aligned CNT array on irregular quartz particles

ABSTRACTVertically aligned carbon nanotube (VACNT) arrays grown on quartz particles were produced in large amount via a floating catalysis process. Initially fast synchronous growth of VACNT arrays was observed, which is independently of the irregular shape and rough surface of the quartz particles. However, long VACNT arrays cracked and scattered anisotropically, depending on the irregular particles. The VACNTs have inner diameter of about 8.0 nm and relatively wide outer diameter distribution with a mean value of 36 nm. The outer diameter of CNTs, however, can be further decreased to 19 nm by tuning carbon source and concentration of catalyst precursor. The VACNTs have a high purity up to 97%. This work presents a simple way for controllable continuous production of VACNT array in large scale.

A 20–40 SECOND PROCESS FOR SYNTHESIS OF MULTI-WALLED CARBON NANOTUBES

We report on a 20–40 s process for growing aligned, uniformed, high purity multi-walled carbon nanotubes (MWNTs) using an alcohol lamp burner. With an appropriate catalyst precursor concentration, MWNTs can be grown on a Co-coated 304 stainless steel mesh under incomplete combustion conditions at 680–700°C. The process provides a rapid, easy, economic and safe method for the formation of carbon nanotubes. We suggest that the proposed method be considered as an educational kit for college or high school level experiments.

Syndiospecific styrene polymerization with CpTiCl3/MAO: Effects of the order of reactant addition on polymerization and polymer properties

AbstractSyndiospecific styrene (St) polymerization, catalyzed by the CpTiCl3/methylaluminoxane (MAO) system, was investigated using two different activation procedures. The polymerization parameters included polymerization time, temperature (∼25–100°C), ratio of [Al]/[Ti] (∼100–1000), and catalyst precursor concentration (∼0.5–10.0 × 10−4 mol Ti/L). It was found that adding reactants in the order of (CpTiCl3 + MAO) + St (Injection of Styrene mode) gave much higher monomer conversion rates, higher weight‐average molecular weights, and narrower molecular weight distributions than for the (St + MAO) + CpTiCl3 (Injection of Catalyst mode). The former also yielded significantly higher syndiotacticity fractions. Differential scanning calorimetry measurements showed multiple peaks exhibiting polymorphism in crystalline syndiotactic polystyrene samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1449–1455, 2004

Fe(NO3)3.9H2O and Fe3(CO)12 as catalyst precursors for the elaboration of VGCF: SEM and TEM study—improvement of the process

Using Grafoil® (Union Carbide) as a substrate, we compare the effect of two catalyst precursors, namely Fe(NO3)3.9H2O and Fe3(CO)12 on the elaboration of carbon fibres. For each precursor, the mass of deposited carbon, of carbon fibres, and especially the fibre length was found to be strongly dependent on the concentration of catalyst precursor over the support. Moreover the methane percentage in the gas mixture plays an important role in the mass of gathered fibres. To observe the modification of the substrate morphology with increasing temperature, several experiments were interrupted at different temperatures within the 900–1110°C range. The results obtained from SEM and TEM revealed that at least two kinds of filaments had grown on the substrate, and that only one of them could give rise to carbon fibres. Precursor filaments were evidenced as having a nanotubular structure and were sometimes agglomerated in bundles. The different stages of fibre growth are also discussed.