Diffusion of Lattice Oxygen during the Reduction and Reoxidation Process of Trisiiver 12-Molybdophosphate

Abstract

Reduction and reoxidation properties of trisilver dodecamolybdophosphate (Ag₃PMo₁₂O₄₀) in solid phase were examined. The rate of reduction was the first order with respect to hydro gen pressure and it had a high dependence on the average degree of oxdidation in the solid. Kinetic isotope effects on the rate of reduction with H₂ or D₂ was not found. A pulse reoxidation method indicated that the oxygen comsumption rate depended on the pulse interval: the longer the intermission, greater the reoxidation rate.
These results are interpreted on the basis of co ncentration gradient of oxide ion in the solid lattice. The high dependence of reduction rate on the average degree of oxidation in the solid is due to the difference between bulk and surface oxide ion concentration. The diffusion coefficients were evaluated by fitting the experimental curve to the theoretical one derived from a basic diffusional equation. The diffusion coefficients of oxide ion in the solid, obtained from both reduction and reoxidation experiments, agree ith one another in the order of magnitude, 10^-12∼10^-13cm²/s. The value is extraordinary high, when compared with that for usu al oxides.