Perovskite type strontium titanate, in which Ti4+ion was partly substituted by Mg2+ and the oxide ion defects were formed, was prepared by doping Mg0 to SrCO3-Ti02 mixture at 1473K. We found that this oxide was active catalyst for the oxidative coupling of methane (0CM) and its activity increased with increasing the amountof oxide ion defects and reached the maximum level at the substitution ratio of 40-60%. The reaction of methane with SrTi0.4Mg0.6O3-δ and SrTiO3 in 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 O2 TPD 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 re-sponsible for the selective oxidative coupling of methane.
A surface reaction occurs on a catalyst surface when the catalyst sample is heated up to a certain temperature in a reactive mixture. After the surface reaction occurs, a steady state is observed without energy supply because the heat produced by the surface reaction is balanced with the heat loss caused by convection, conduction and radiation. The heat release of the surface reaction can be evaluated by the surface temperature of the catalyst sample at the steady state. This paper treats the effects of the equivalence ratio (ER) and the dilution ratio (DR) of the reactive mixture on the surface reaction. Hydrogen and oxygen are used as reactive mixture and nitrogen as inert gas. The height, width and length of the combustion chamber are 76mm, 140mm and 140mm, respectively. A spherical Pt catalyst sample of 1.5mm in diameter is sustained in the chamber with two wires of 0.1 mm in diameter. The chamber is filled with a hydrogen-oxygen-nitrogen mixture at the atmospheric pressure and the room temperature. The surface temperature is measured with a thermocouple. As the results, the heat produced by the surface reaction decreases with increasing dilution ratio, and hydrogen is adsorbed more easily compared with oxygen.
Dehydrogenative coupling of methane in the thermal diffusion reactor was carried out, using a carbon rod and a tungsten wire as pyrogens. Pyrogens were studied of durability, reaction activity and electric power required. Three results were obtained. 1) 3.0mm of carbon rod made from carbon black and artificial graphite exhibits high persistence at high reaction temperature. 2) The reaction rate of methane per surface area of carbon rod used as pyrogen is same as that of tungsten wire. 3) At the limit temperature of pyrogen reuse, the electricity consumption of carbon rod for getting the specified activity is about 1.7 times that of tungsten wire.