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The oxidative coupling of methane (OCM) is a type of chemical reaction discovered in the 1980s for the direct conversion of natural gas, primarily consisting of methane, into value-added chemicals. Direct conversion of methane into other useful products is one of the most challenging subjects to be studied in heterogeneous catalysis. Methane activation is difficult because of its thermodynamic stability with a noble gas-like electronic configuration. The tetrahedral arrangement of strong C–H bonds (435 kJ/mol) offer no functional group, magnetic moments or polar distributions to undergo chemical attack. This makes methane less reactive than nearly all of its conversion products, limiting efficient utilization of natural gas, the world’s most abundant petrochemical resource. == Ethylene production == The principal product of OCM is ethylene, the world’s largest commodity chemical and the chemical industry's fundamental building block. While converting methane to ethylene would offer enormous economic benefits, it is a major scientific challenge. Thirty years of research failed to produce a commercial OCM catalyst, preventing this process from commercial applications. Ethylene production is an estimated $160 billion/year. Ethylene derivatives are found in food packaging, eyeglasses, cars, medical devices, lubricants, engine coolants and liquid crystal displays. Ethylene production by steam cracking consumes large amounts of energy, uses valuable oil fractions, such as naphtha and is the largest contributor to Greenhouse gas emissions in the chemical industry. The oxidative coupling of methane to ethylene is written below:〔Olah, G., Molnar, A. “Hydrocarbon Chemistry” John Wiley & Sons, New York, 2003. ISBN 978-0-471-41782-8.〕 : 2 + → + 2 The reaction is exothermic (∆H = -280 kJ/mol) and occurs at high temperatures (750–950 ˚C). In the reaction, methane () is activated heterogeneously on the catalyst surface, forming methyl free radicals, which then couple in the gas phase to form ethane (). The ethane subsequently undergoes dehydrogenation to form ethylene (). The yield of the desired products is reduced by non-selective reactions of methyl radicals with the surface and oxygen in the gas phase, which produce (undesirable) carbon monoxide and carbon dioxide. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oxidative coupling of methane」の詳細全文を読む スポンサード リンク
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