The active phase in sodium-doped calcium oxide catalysts for oxidative coupling of methane

The reactivity of pure and sodium-promoted calcium oxide catalysts toward the oxidative coupling of methane at 640°C has been investigated. While the pure calcium oxide was essentially a combustion catalyst, sodium-promoted calcium oxide exhibited significant C₂ productivity. Study of the deactivation of both pure and promoted catalysts demonstrated that the presence of calcium oxide was necessary for both catalysts to be active. This observation, combined with the effects of sodium doping on C₂ selectivity, suggests that the active phase on Na/CaO catalysts toward C₂ formation consists of sodium species associated with calcium oxide. This active phase was destroyed when calcium oxide was converted into calcium carbonate under reaction conditions.