Controlling the yield and structure of carbon nanofibers grown on a nickel/activated carbon catalyst (original) (raw)
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Applied Catalysis A: General, 2007
Carbon nanofibers (CNFs) were prepared by the catalytic decomposition of ethylene over Ni/Y-zeolite at 550 8C, followed by catalyst removal with hydrofluoric acid. The demineralised CNFs were impregnated in an aqueous solution of Ni(II) nitrate. The CNF-supported Ni exhibited high catalytic activity in the CVD synthesis of CNFs, proving that the structured CNF support served to stabilize Ni activity. Results clearly indicated that careful control of temperature and H 2 content was important to achieve the desired product. Changing the total flow rate did not seem to alter the type of carbon deposited but did change the deposition rate. #
Growth of Carbon Nanofibers on Ni-Catalysts by Chemical Vapor Deposition Method
Advanced Science, Engineering and Medicine, 2012
High quality, uniform distribution and rather straight carbon nanofibers (CNFs) with diameter between 10-100 nm were produced by catalytic chemical vapor deposition (CCVD) method. We also prepared multiwalled carbon nanotubes (MWCNTs) by this method. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and FT-Raman scattering. CNFs were synthesized at 450-800 C using Ni-based catalyst. Nickel was deposited on clinopetilolite (a natural zeolite), alumina and carbon as support. Acetylene and, hydrogen and argon were used as carbon source and as carrier respectively. It was found that Ni/clinoptilolite catalyst exhibited a best catalytic activity for growth of CNFs at the temperature between 600-700 C. The effect of various experimental parameters such as: supports type, reaction temperature, acetylene and hydrogen flow rate, were investigated.
Topics in Catalysis, 2007
Carbon nanofibers (CNFs) with a uniform diameter of ca. 30 nm have been grown via catalytic decomposition of C 2 H 6 /H 2 mixture over a nickel (1 wt.%) catalyst supported on graphite microfibers which constitutes the macroscopic shape of the final C/C composite. The productivity reached 50 g of CNFs / g of Ni / h on stream and is among the highest reported to date. The resulting composite consisting in a web-like network of CNFs covering the starting catalyst was characterized by SEM and TEM in order to get more insight on the relationship between the starting nickel catalyst particles and the as-grown CNFs. Apparently the CNFs growth proceeds from different mechanisms: base-growth mechanism involving especially the large nickel particles, tip-growth mechanism involving the smaller nickel particles and tip/octopus-growth mechanism, the most frequent involving all particles. The restructuration of the nickel particle from a globular to a more faceted structure seems to be the key step to produce an extremely large quantity of CNF with yields up to 100 wt.% after 2 h of synthesis.
Production of carbon nanofibers (CNFS) on impregnated activated carbon
2008
Carbon nanofibers (CNFs) were synthesized by catalytic decomposition of benzene, as carbon source, on powdered activated carbon (PAC) impregnated with 3% of nickel (II) in acetone. The calcination and reduction of the impregnated PAC were conducted in presence of pure N 2 at 350ºC and H 2 gas at 400ºC, respectively. The synthesis occurred in a tubular chemical vapour deposition (CVD) reactor at atmospheric pressure in presence of benzene and hydrogen at 680ºC for 1 hour. SEM, TEM and TGA were used for the characterization of the product. Growth of CNFs was uniform over the nickel impregnated activated carbon substrates with most of their diameters ranging from 95 to 140 nm.
About the octopus-like growth mechanism of carbon nanofibers over graphite supported nickel catalyst
Journal of Catalysis, 2006
Carbon nanofibers (CNFs) with a uniform diameter of ca. 30 nm and a productivity of 50 g/(g Ni h) were grown by catalytic decomposition of a C 2 H 6 /H 2 mixture over a nickel (1 wt%) catalyst supported on graphite microfibers, which constitutes the macroscopic shape of the final C/C composite. The catalyst particle size and dispersion before CNF growth was characterized by high-resolution scanning electron microscopy (SEM). The resulting composite consisting of a weblike network of CNFs covering the starting catalyst was characterized by SEM and transmission electron microscopy to gain more insight into the relationship between the starting nickel catalyst particles and the as-grown CNFs. Apparently, CNF growth proceeds from different mechanisms: a base-growth mechanism, involving especially the large nickel particles; a tip-growth mechanism, involving mostly the smaller nickel particles; and a tip/octopus-growth mechanism (the most common), involving all particles. In all cases, restructuring of the nickel particle from a globular to a more faceted structure seems to be the key step in producing an extremely large quantity of CNFs with yields up to 100 wt%.
Synthesis and Characterization of Carbon Nanofibers Grown on Powdered Activated Carbon
Journal of Nanotechnology, 2016
Carbon nanofibers (CNFs) were synthesized through nickel ion (Ni 2+) impregnation of powdered activated carbon (PAC). Chemical Vapor Deposition (CVD) using acetylene gas, in the presence of hydrogen gas, was employed for the synthesis process. Various percentages (1, 3, 5, and 7 wt. %) of Ni 2+ catalysts were used in the impregnation of Ni 2+ into PAC. Field Emission Scanning Electron Microscope (FESEM), Fourier Transform Infrared (FTIR) Spectroscopy, Energy Dispersive X-Ray Analyzer (EDX), Transmission Electron Microscopy (TEM), Thermal Gravimetric Analysis (TGA), zeta potential, and Brunauer, Emmett, and Teller (BET) were utilized for the characterization of the novel composite, which possessed micro and nanodimensions. FESEM and TEM images revealed that the carbonaceous structure of the nanomaterials was fibrous instead of tubular with average width varying from 100 to 200 nanometers. The PAC surface area increased from 101 m 2 /g to 837 m 2 /g after the growth of CNF. TGA combustion temperature range was within 400 ∘ C and 570 ∘ C, while the average zeta potential of the nanocomposite materials was −24.9 mV, indicating its moderate dispersive nature in water.
Synthesis of carbon nanofibers on impregnated powdered activated carbon as cheap substrate
The catalysis and characterization of carbon nanofibers (CNFs) composite are reported in this work. Carbon nanofibers were produced on oil palm shell powdered activated carbon (PAC), which was impregnated with nickel. Chemical Vapor Deposition (CVD) of C 2 H 2 was used in the presence of hydrogen at $650°C. The flow rates of carbon source and hydrogen were fixed. The CNFs formed directly on the surface of the impregnated PAC. Variable weight percentages (1%, 3%, 5%, 7% and 9%) of the catalyst salt (Ni +2 ) were used for the impregnation. However, the best catalysis was observed on the substrate with 3% Ni +2 . The product displayed a relatively high surface area, essentially constituted by the external surface. New functional groups also appeared compared to those in the PAC. Field Emission Scanning Microscopy (FESEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FTIR), BET surface area analysis and energy dispersive X-ray (EDX) were used for the characterization of the new carbon nano product, which was produced through a clean novel process. ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.
Synthesis of carbon nanofibers: effects of Ni crystal size during methane decomposition
Journal of Catalysis, 2005
The effect of the crystal size of Ni on the growth of carbon nanofibers (CNFs) was studied in a tapered oscillating element microbalance reactor. Small Ni crystals yield a low growth rate and fast deactivation and thus a low final yield of CNF. Large Ni crystals reduce the growth rate because of low surface area. An optimum growth rate and yield of carbon nanofibers can be achieved on optimally sized Ni crystals (around 34 nm). A model has been proposed for interpreting the kinetic effects of the Ni crystal size based on a detailed mechanism of the carbon nanofiber growth. The reduced coking rate on a small-sized Ni crystal is a result of increased saturation concentration of CNF and thus a low driving force for carbon diffusion through the Ni crystals. As a consequence, the surface coverage of carbon increases, which enhances the formation of encapsulating carbon and thus the deactivation. Both the low initial coking rate and the fast deactivation result in a low yield of carbon nanofibers on small-sized crystals. The results also indicate that hydrogen has a significant effect on the formation of CNF, and an optimum partial pressure of hydrogen exists for the CNF growth.
Carbon, 2006
Carbon nanofibers (CNF) are non-microporous graphitic materials with a high surface area (100-200 m 2 /g), high purity and tunable surface chemistry. Therefore the material has a high potential for use as catalyst support. However, in some instances it is claimed that the low density and low mechanical strength of the macroscopic particles hamper their application. In this study we show that the bulk density and mechanical strength of CNF bodies can be tuned to values comparable to that of commercial fluid-bed and fixed-bed catalysts. The fibers were prepared by the chemical decomposition of CO/H 2 over Ni/SiO 2 catalysts. The resulting fibers bodies (1.2 m mm) were replicates of the Ni/SiO 2 bodies (0.5 mm) from which they were grown. The bulk density of CNF bodies crucially depended on the metal loading in the growth catalyst. Over 5 wt% Ni/SiO 2 low density bodies (0.4 g/ml) are obtained while 20 wt% Ni/SiO 2 leads to bulk densities up to 0.9 g/ml with a bulk crushing strength of 1.2 MPa. The 20 wt% catalysts grow fibers with diameters of 22 nm, which grow irregularly in space, resulting in a higher entanglement and a concomitant higher density and strength as compared to the thinner fibers (12 nm) grown from 5 wt% Ni/SiO 2 .
Metals, 2018
Mechanical alloying (MA) has been and continues to be thoroughly examined for creating structural materials, but the production of catalysts is relatively rare. This is especially true for catalysts used in the production of carbon nanofibers (CNFs), a versatile material for applications such as energy storage, catalyst support, advanced composites and others. The application of MA to create CNFs presents a valuable tool in reducing their cost and complexity, and thereby may increase their commercial potential. In this study, the effects of milling duration on CNF deposition are studied by the complementary methods of X-ray diffraction, compositional mapping, electron microscopy, particle size analysis and surface area analysis. These were used to determine microstructural and macroscale evolution of the catalyst powder and its effects on the kinetics and characteristics of carbon deposition using Ni and Ni 30 at % Cu. The results have important implications for low cost catalyst production and provide general guidance on the development of catalytic materials in miscible systems.