AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM4
Oxidative Coupling of Methane to Higher Hydrocarbons Using Li@sub 2@O/MgO Catalysts

Tuesday, November 5, 2002, 9:20 am, Room C-108

Session: Hydrocarbon Catalysis
Presenter: F. Behrendt, Technische Universität Berlin, Germany
Authors: J. Langohr, Technische Universität Berlin, Germany
R. Heinisch, Technische Universität Berlin, Germany
F. Behrendt, Technische Universität Berlin, Germany
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Oxidative coupling of methane represents an important pathway to produce higher hydrocarbons especially those with two carbon atoms, i. e, ethane and ethane, representing a key component for chemical industry. The reaction scheme ­ which still is not completely understood -involves a number of steps with the heterogeneous formation of methyl radicals and the homogeneous recombination of methyl radicals to ethane as key parts. The second of these reactions is in competition with reactions leading to the total oxidation products carbon dioxide and water ­ a pathway occurring both homogeneously and heterogeneously. With respect to the concentration of methyl radicals the reaction order is one for the total oxidation but two for the formation of ethane. An increase of the concentration of methyl radicals should promote an increased production of the C@sub 2@ hydrocarbons. For the example of a set of Li@sub 2@O/MgO catalysts it is shown that an increase of the BET surface area ­ resulting in a higher number of active sites at the catalyst¹s surface ­ results in an increased yield of C@sub 2@ hydrocarbons. By variation of the preparation technique (aqueous mixtures of various Li and Mg salts are dried and then calcinated at different temperatures and periods of time) catalysts are produced which indeed show an increase in methane turn-over - without losing selectivity for C@sub 2@ hydrocarbons - with increasing surface area. The BET surface area is varied between 0.3 and 4.2 m@super 2@/g. Ongoing experiments aim at further increasing this surface area. Modifications of the preparation technique will include calcination under low-pressure conditions and on carrier materials having high surface areas themselves, e. g., polyurethane foams or activated carbon.