Abstract
Natural manganese oxides were evaluated as oxidative coupling catalysts to convert methane into C 2-hydrocarbons. Reactions were done in a cyclic redox mode in which the oxidized catalyst was reacted with methane at 850°C in the absence of oxygen. The bulk and surface analyses (XRD, XPS, FT-IR) indicate that the catalyst deactivation in the methane atmosphere is related to reduction of manganese ions, oxygen depletion of the catalyst surface and formation of manganese carbide species. It is proposed that the XPS line of OIs electrons, Eb = 528.6 eV should be assigned to the surface oxygen bound to the reduced Mn 2+ cation with close oxygen vacancies, and lines of Mn2p 3/2 electrons, Eb = 641 eV and C1s at 282.5 eV may be assigned to the surface manganese carbide.
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