Oxidative Coupling of Methane on Strontium Titanate with Oxide Ion Defects—Structure and catalytic activity–

Perovskite type strontium titanate, in which Ti⁴⁺ion was partly substituted by Mg²⁺ and the oxide ion defects were formed, was prepared by doping MgO to SrCO₃-TiO₂ mixture at 1473K. We found that this oxide was active catalyst for the oxidative coupling of methane (OCM) and its activity increased with increasing the amount of oxide ion defects and reached the maximum level at the substitution ratio of 40-60%. The reaction of methane with SrTi_0.4Mg_0.6O_3-δand SrTiO₃in the absence of oxygen gave C₂ hydrocarbons and COx. The selectivity at the initial stage agreed with that of the steady-state catalytic reaction of the oxidative coupling of methane. From these results and O₂TPD result which has been reported, it is suggested that the addition of Mg²⁺ modify the reactivity of the lattice oxide ion and the lattice oxide ion, which desorbed in the temperature range 873 K-1273 K on TPD measurement, is responsible for the selective oxidative coupling of methane.