Effect of stability and diffusivity of extra-framework oxygen species on the formation of oxygen radicals in 12CaO·7Al2O3

The thermodynamics and kinetics of oxygen radical formation process in a nanoporous crystal, 12CaO·7Al2O3, were examined by isothermal annealing experiments in dry atmospheres. It is clarified that the formation of oxygen radicals, O2− and O−, in the crystal occurs in the following three steps; outward diffusion of extra-framework oxide ions, its oxidation by absorbed oxygen molecules to form O− and O2− at the surface, and subsequent inward diffusion of the oxygen radicals. The instability of the extra-framework oxide ions is essentially the driving force for the process. Further, the analyses allow to predict the total oxygen radical content for a given annealing condition.