Temperature-Programmed Studies of Surface Oxygen Species in the Oxidative Coupling of Methane

The reactivity of surface oxygen species for the oxidative coupling of methane over various catalysts, [Sm2O3, Li(5%)-Sm2O3, Li-MgO, Bi-P-K/MgO, Bi-P-Na/MgO, and a series of catalysts of the general composition MBi1-xLixOy/MgO, where M=Sr, Ba; x = 0, 0.05, 0.15, 0.20, 0.40, 0.50], has been investigated by means of temperature-programmed desorption (TPD), temperature-programmed reaction (TPRX), and temperature-programmed reduction (TPR) between 100–800°C. The experimental results suggest that simple, adsorbed oxygen species are not the active species for oxidative coupling of methane. Instead, they are responsible for deep oxidation. Simple-oxide catalysts are active only in the presence of gaseous oxygen. For multicomponent-oxide catalysts, surface lattice oxygen directly participates in the reaction, giving a high selectivity toward C2 products.