The oxidative conversion of methane to higher hydrocarbons over alkali-promoted Mn/SiO2

Abstract Increased yields of higher hydrocarbons from methane over manganese oxide-silica are obtained upon the addition of alkali metals and alkaline earths to the catalyst. Running redox cycles of alternating methane and air, a 15% manganese-5% sodium pyrophosphate-silica catalyst repeatedly gives a 17% yield of ethane, ethylene, and higher hydrocarbons (77% selectivity and 22% conversion) for 2 min at 850 °C and 860 GHSV. This represents an improvement of 40 absolute percent selectivity over the alkali-free catalyst. The improvement arises largely by suppression of product oxidation. Further evidence is described for a mechanism involving surface-initiated gas phase methyl radicals.