Adsorption and decomposition of nitrous oxide on γ-irradiated magnesium oxide

Abstract

The decomposition of nitrous oxide has been investigated over magnesium oxide at temperatures between 423 and 773 K with and without the influence of γ-irradiation. Initial pressures of 8.0 and 7330 N m^–2(0.06 and 55 Torr) of N₂O were used. Measurements of the decomposition of 7330 N m^–2 of N₂O in which the system was continuously γ-irradiated, indicated that two processes of activation energy, E_a, of 148.8 ± 5.0 kJ mol^–1 and 39.9 ± 4.0 kJ mol^–1 were operative above and below ca. 720 K respectively. The thermal catalytic decomposition of 7330 N m^–2 of N₂O occurred over the complete temperature range 673 to 773 K with a value of E_a of 148.8 ± 5.0 kJ mol^–1. It was concluded that the radiation catalytic process below ca. 720 K occurred via ionic intermediates, (N₂O^–|□^–_s)_ads, which were produced by the interaction of gaseous N₂O molecules with radiation induced F⁺_s centres on the surface of the magnesia. Both the radiation catalytic decomposition above ca. 720 K and the unirradiated process probably occurred without an electron transfer process. The low pressure (8.0 N m^–2) thermal decomposition also proceeds via the ionic intermediate at temperatures between 423 and 553 K.

Adsorption of N₂O could be detected on unirradiated MgO between 77 and 294 K. On γ-radiolysis, however, the decomposition of these physically adsorbed species was induced. The effect of pre-adsorbed oxygen is studied and post-irradiation effects are discussed.