THE ROLE OF SODIUM-CARBONATE AND OXIDES SUPPORTED ON LANTHANIDE OXIDES IN THE OXIDATIVE DIMERIZATION OF METHANE

The addition of Na2CO3 to three representative lanthanide oxides, La2O3, CeO2, and Yb2O3, has a marked effect on the catalytic properties of these materials for the oxidative dimerization of methane. The effect is most dramatic for CeO2, which, upon addition of Na2CO3, is transformed from a total oxidation catalyst to one which is reasonably selective for the conversion of CH4 to C2H4 and C2H6. Results obtained by X-ray photoelectron spectroscopy and ion scattering spectroscopy show that a sodium carbonate /sodium oxide phase largely covers the lanthanide oxide surface, thus the catalytic properties are those of the sodium phase, rather than those of the lanthanide oxide. Indeed, the specific activities of the Na+/LnxOy catalysts and of pure Na2CO3 were the same within a factor of 2.5, with Na+/Yb2O3 at the high end of the range. The specific activities of pure lanthanide oxides were considerably greater than those of the modified catalysts. Although Na2CO3 is the principal compound present on the surface of the Na+/LnxOy catalysts, it is probable that Na2O2 is responsible for the activation of CH4. © 1990.