Synthesis Of Carbon Nanotubes Via Decomposition Of Methane Using Carbon Supported Catalysts
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Date
2011-05
Authors
Murugaiyan, Sivakumar Vaiyazhipalayam
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Publisher
Universiti Sains Malaysia
Abstract
Carbon nanotubes (CNTs) with their special properties find applications in many areas. Owing to its global demand, its synthesis at a cheaper cost is inevitable. In this study, low-cost carbon materials like carbon molecular sieves (CMS-G, CMS-IN) and activated carbon (AC) were examined as supports for three different active metals (Ni, Co and Fe) for methane chemical vapour decomposition (m-CVD) process to produce CNTs. Blank studies and active metal impregnated (5, 10 and 15 wt% loadings) catalysts activity were studied at temperatures 650, 750 and 850 oC for maximum methane (CH4) conversion and optimum CNTs growth. The synthesized metal catalysts over AC support were relatively better in CH4 conversion and formed CNTs compared to CMS type supports. In-depth analysis of individual catalysts like Ni/AC, Co/AC and Fe/AC were made by varying the parameters of catalyst preparation and reaction conditions. 5 wt% Ni/AC catalysts calcined at 350 oC, reduced at 550 oC was found to give maximum CH4 conversion of 96.81% at 850 oC. Higher population of CNTs with average internal diameter of 14 nm and thickness of 3 nm was obtained under these conditions. SEM/EDX analyses were used to confirm the formed CNTs and metal content on synthesized catalysts. Methane to nitrogen (CH4:N2) gas ratio of 1:2 was found to posses prolonged catalyst activity better than a ratio of 1:3. Temperature programmed reduction profiles (TPR) of Ni/AC catalyst showed that nickel oxides NiO formed below 450 oC. TEM study of product samples revealed that multi-walled carbon nanotubes (MWNTs) with thin and broader filamentous type having average internal diameters of around 2.5 and 27 nm, respectively were formed over 5 wt% Ni/AC catalyst under different preparation and reaction conditions. Similarly, Co/AC catalyst with 15 wt% loading, calcined at 350 oC and reduced at 450 oC recorded a maximum CH4 conversion of 89% at 850 oC. Twisted ribbon-like MWNTs with average internal diameter of around 16 nm were formed. Fe/AC catalysts with 5 wt % loading reported maximum CH4 conversion of 98.6% at 750 oC. Prolonged catalyst activity of longer than 2 h was demonstrated by 5 wt% Fe/AC catalyst compared to the other catalysts.
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Keywords
Synthesis of carbon nanotubes via decomposition , of methane using carbon supported catalysts