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|Title: ||Oxidative Dimerization of Methane over a Lithium-Promoted Magnesium Oxide Catalyst|
|Authors: ||Tomoyasu Ito;Wang, Ji-Xiang;Lin, Chiu-Hsun;Jack H. Lunsford|
|Issue Date: ||2013-06-05T09:35:32Z
|Publisher: ||American Chemical Society|
|Abstract: ||Lithium-promoted magnesium oxide was used as a catalyst for the partial oxidation of methane by molecular oxygen|
in a conventional flow reactor. Ethane and ethylene (C, compounds) were obtained with 50% selectivity at a 38% conversion of CHI over 4 g of 7 wt % Li-promoted MgO at 720 OC. The initial reactant mixture had a CH, to O2 ratio of ca. two. The other products were CO and CO,. In this reaction system both the C, selectivity and the CH, conversion increased with an increase in reaction temperature up to ca. 700 OC. All catalysts doped with 1 to 26 wt % Li were effective in the C2 production, while undoped and 0.2 wt % Li-promoted MgO caused nonselective oxidation. EPR spectroscopy revealed that [Li'O-] centers probably were the active sites responsible for initiating the reaction by abstracting a hydrogen atom from CH,. The [Li'O-] centers exist in an equilibrium state only at high temperatures in the presence of oxygen. Based on kinetic analyses a mechanism has been proposed in which most of the products, including CO and CO,, are produced via CH,.; the coupling of two CH3. leads to C2H,, which is partly oxidized to C2H4. Below 700 "C CO and CO, are produced by reactions of CH3. with either surface 0,- ions or gaseous 0,. The latter reaction leads to chain reactions in which additional methyl radicals are generated. The Li-promoted MgO contains no transition metals; thus it is a new type of oxidation catalyst on which thermally generated 0- ions activate methane.
|Relation: ||Journal of the American Chemical Society, 107(18): 5062-5068|
|Appears in Collections:||[化學系] 期刊論文|
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