Synthesis of multiwalled carbon nanotubes on Al₂O₃ supported Ni catalysts in a fluidized‐bed

Abstract

Multiwalled carbon nanotubes (MWNTs) were synthesized on Al 2 O 3 supported Ni catalysts from C 2 H 2 and C 2 H 4 feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/U mf ), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized-bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by-product. V

Evaluating the Environmental Impacts of a Nano-Enhanced Field Emission Display Using Life Cycle Assessment: A Screening-Level Study

“…For the purpose of this work, the stages of material acquisition and product manufacturing will be collectively referred to as “manufacturing”. The LCI data corresponding to production of the metal catalyst and synthesis of CNTs are based on the carbon deposition yields (CDYs) and synthesis reaction yields (SRYs) reported in Fazle-Kibria et al, Leone, and Liu and Harris for the use of acetylene with a bimetallic nickel and iron catalyst supported on aluminum oxide. CNTs produced via bimetallic catalyst systems have shown the ability to generate higher field emission efficiencies than those synthesized via monometallic catalytic systems .…”

Controlled Synthesis of Ferromagnetic Semiconducting Silicon Nanotubes

“…The SiNTs have been produced by a conventional CVD technique (at temperatures below the Si–Ni eutectic point). The use of Ni/Al 2 O 3 as catalyst for methane decomposition is a well-known route for the growth of CNTs. − Also, metal nickel (and copper) substrates were shown to act as an effective catalyst for the decomposition of gaseous silane and germane precursors at a broad range of temperatures . We found that Ni/Al 2 O 3 , simply by dipping the AAO membrane in a Ni solution, served as an excellent catalyst for the chemical decomposition of silane onto the AAO pore surface, thus enabling the controllable formation of SiNTs.…”

“…During the growth process, once SiH 4 starts to flow at a temperature of 450 °C, it reduces the absorbed Ni 2+ to form Ni Red /Al 2 O 3 clusters on the membrane surface or alternatively to form Ni x Si y (nickel silicide) crystalline clusters. The Ni Red /Al 2 O 3 (or NiSi/Al 2 O 3 ) clusters serve as catalysts for further SiH 4 decomposition resulting in absorption of Si onto the membrane’s nanochannel inner surfaces, in a manner similar to the decomposition of methane during CNT growth. − The absorbed Si serves in turn to catalyze the decomposition of SiH 4 and encourages the continuous growth of the SiNTs. Nickel atoms can diffuse into the forming silicon layer, spreading evenly into the SiNT walls volume, at the growth temperatures between 450 and 650 °C.…”

Fluidization and Application of Carbon Nano Agglomerations

“…In 2009, Harris et al. [ 94 ] systematically studied the crucial factor of the ratio between superficial gas velocity and minimum fluidization velocity during the fluidization growth of MWCNTs. They discovered that as reaction time increased, pressure drop in the fluidized bed also increased.…”