The oxidation of methane with oxygen-18 to carbon dioxide and water at 400 °C has been examined on a series of antimony–tin oxide catalysts containing up to 17.9% antimony. The otherwise high rates of exchange of oxygen between the products and catalysts were suppressed by freezing out the former as they were generated. This technique permitted the application of the isotope kinetics described in the previous paper. Thus the participation of both adsorbed and lattice oxygen in the formation of carbon dioxide has been confirmed and the relative activities of the two forms measured. It was found that utilisation of adsorbed oxygen, substantial on tin oxide, decreased sharply with increasing antimony content in the mixed-oxide catalysts, being completely suppressed on the 17.9% antimony-containing catalyst.

Rates of exchange of oxygen with the same catalyst series, measured at 580 °C, were also found to decline with increasing antimony content, as did the relative importance of the heteromolecular exchange process between a molecule of oxygen and one lattice oxygen atom compared with exchange with two lattice atoms.

The results obtained in the oxidation and exchange experiments are compared and possible mechanisms advanced for the interaction of oxygen with antimony–tin oxide catalysts.