The Role of [M+O−] Centers (M+– Group IA Ion) in the Activation of Methane on Metal Oxides

If the ionic radii are compatible, alkali metal ions will substitute for the divalent metal ions in magnesium oxide, calcium oxide and zinc oxide. At high temperatures in the presence of molecular oxygen, centers of the type [M+O−] are formed, where MM+– Group IA ion. The O− ions in equilibrium with these centers are effective in H” abstraction from CH4, which is the first step in the oxidative dimerization reaction. At reaction temperatures >720°C alkali metal oxides formed on the catalytic surface may themselves become active centers. Alkali metal carbonates also may inhibit the activity of the host oxide and sinter the oxide, thereby eliminating corner sites which result in complete oxidation.