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The process of methane oxidative coupling (MOC) is promising for the development of methane-based industries. Many papers exist on the preparation of catalysts and the mechanism of the reaction. In the MOC reaction, methane is supposed to be activated through abstraction of an H atom from CH[sub 4] by an active oxygen species. Lunsford and his co-workers detected (Li[sup +]O[sup [minus]]) centers in an Li/MgO catalyst by ESR and proposed that O[sup [minus]] species were responsible for the activation of methane over Li/MgO. For TiO[sub 2]-based catalysts, when TiO[sub 2] alone was used as a catalyst, whether as anatase or rutile, little or no coupling activity was observed. However, the addition of Li drastically improved the selectivity to C2 hydrocarbons, with optimum effectiveness at 10 wt% or 16.2 wt% Li. At selected conditions, the selectivity to C2 hydrocarbons and the conversion of methane reached 75.3 and 13.5%, respectively, for a 10-wt% Li/TiO[sub 2] catalyst. Therefore, it is interesting to study the role of Li and other promoters in the MOC reaction. In this paper the authors report the results of a dynamic ESR study for O[sub 2] chemisorption on model TiO[sub 2]-based catalysts to elucidate the active species which existmore » on the surface of catalysts.« less |
