Enhanced Activation and Decomposition of CH4 by the Addition of C2H4 or C2H2 for Hydrogen and Carbon Nanotube Production

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• 作者：Weizhong Qian ; Tao Tian ; Chenyi Guo ; Qian Wen ; Kuangjie Li ; Hongbo Zhang ; Haibo Shi ; Dezheng Wang ; Yi Liu ; Qiang Zhang ; Yongxiong Zhang ; Fei Wei ; Zhanwen Wang ; Xiaodong Li ; Yongdan Li
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：May 22, 2008
• 年：2008
• 卷：112
• 期：20
• 页码：7588 - 7593
• 全文大小：1436K
• 年卷期：v.112,no.20(May 22, 2008)
• ISSN：1932-7455

文摘

The decomposition of CH₄ in the presence of C₂H₄ or C₂H₂ using a nanosized iron or nickel based catalyst with volume ratios of C₂H₄ or C₂H₂ to CH₄ of 1.75:1 to 0.55:1 was investigated. The presence of C₂H₄ or C₂H₂ increased the conversion of CH₄ to 3 to 5 times that with no C₂H₄ or C₂H₂; that is, it significantly increased the production rate of carbon from 20−30 to 45–75 g/gcat/h at 723–873 K. The online detection of the time dependent composition of the product gas and experiments in which the feeding sequence of CH₄ and C₂H₄/C₂H₂ was changed allowed us to propose a mechanism for the enhanced decomposition as follows. First, the facile exothermic adsorption and decomposition of C₂H₄ or C₂H₂ provides the driving force for the in situ endothermic decomposition of CH₄. Subsequently, the thermodynamically favored intermediate products of aromatics or poly aromatics are formed by the insertion of CH₄ into adsorbed C₂H₄ or C₂H₂ fragments. Finally, the intermediate products are rapidly dehydrogenated on the high activity catalyst to form carbon nanotubes (CNTs). The enhancement effect is dependent on the ratio of C₂H₄ to CH₄ but independent of the ratio of C₂H₂ to CH₄, which was explained as being due to the different exothermicities of the C₂H₄ and C₂H₂ reactions. This finding provides a new stimulus for methane activation at low temperature to produce hydrogen and CNTs with high efficiency.