SURFACE-COMPOSITION AND SELECTIVITY OF SODIUM-COMPOUND-IMPREGNATED CALCIUM-OXIDE CATALYSTS FOR THE OXIDATIVE COUPLING OF METHANE

CaO was impregnated with different sodium compounds (NaNO3, NaOH, NaBH 4, NaNH2, Na2CO3), dried and calcined (873-1023 K). For these material s, which were used as catalysts in oxidative methane coupling (OCM), s urface compositions were determined by X-ray photoelectron spectroscop y after drying, calcining and exposure to OCM. Surface composition dep ends on the type of precursor used, its bulk amount and calcination te mperature. After exposure to OCM surface sodium content decreases. C-2 + selectivity is markedly affected by the sodium content on the surfac e, a minimum content of approximately 30 at.-% of sodium is required f or maximum selectivity.