OXIDATIVE COUPLINGS OF METHANE, ETHANE, AND PROPANE WITH SODIUM PEROXIDE AT LOW-TEMPERATURES

Partial oxidations of CH4, C2H6, and C3H8 proceeded over sodium peroxide at low temperatures (600-650 K). The only partial oxidation product from CH4 was ethane, a coupling product. The quantity of its formation depended on the second order of the methane pressure. The products from C2H6 were ethylene and butane. The formation rate of ethylene depended on the first order but that of butane depended on the second order of the ethane pressure. In the case of C3H8, the products were C6 alkanes, C4 alkanes, ethylene, and traces of propylene. The formation rates of C6 and C4 alkanes depended on the second order but those of ethylene and propylene depended on the first order of the propane pressure. The activation energies for the conversions of CH4 (127 kJ mol-1) were considerably larger than those of C2H6 (83) and C3H8 (89). The transition state of CH4 in its activation is suggested to be different from those of C2H6 and C3H8. The presence of gaseous oxygen decreased the selectivities to the coupling products and to the dehydrogenation products, although the rates of conversion of alkanes were not affected by gaseous oxygen. These observations suggest that the activation of alkanes is caused only by peroxide anions, but the selectivities to further reactions of the surface alkyl groups formed are affected strongly by the presence of gaseous oxygen. © 1990.