It was found that under the reaction conditions suitable for oxidative coupling of methane over a half of ethylene formed from the ethane-oxygen feedstock in the presence of Na+/CaO catalyst may derive from thermal transformations of ethane rather than from its oxidative dehydrogenation. The total selectivity of ethane conversion towards all hydrocarbons formed is high and at 1073 K is close to 99%. The selectivity of ethylene formation is about 86 - 88% at 873 K. An increase in the temperature to 923 K causes an approximately 10% decrease in the ethylene selectivity. However, at about 973 K ethylene selectivity returns to the level of 87 - 90% which is sustained until 1073 K. The minimum selectivity of ethylene formation is accompanied by the corresponding maxima in C3+ hydrocarbons and methane selectivities, which suggest that disproportionation of C2 species is favoured at 873 - 973 K.
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