The diffusion of hydrogen in sodium aluminum sodalite was modelled, allowing full flexibility of the host framework, at 800 to 1200K. From the simulations, the self-diffusion coefficient was determined as a function of temperature, and the hydrogen uptake at low equilibrium hydrogen concentrations was estimated at 573K. The influence of the cation distribution upon hydrogen self-diffusion was investigated by comparing results, involving a low-energy fully-ordered cation distribution, with those obtained using a less ordered distribution. The cation distribution was found to have a surprisingly large influence upon the diffusion, which appeared to be due to the difference in framework flexibility for different cation distributions, the occurrence of correlated hopping in the case of an ordered distribution and the differing natures of the diffusion processes in each system. Compared to previously reported calculations on all silica sodalites, the hydrogen diffusion coefficient of this sodalite was higher in the case of an ordered distribution and lower in case of a disordered one.

Effect of Cation Distribution on Self-Diffusion of Molecular Hydrogen in Na3Al3Si3O12 Sodalite: a Molecular Dynamics Study. Van Den Berg, A.W.C., Bromley, S.T., Flikkema, E., Jansen, J.C.: Journal of Chemical Physics, 2004, 121[20], 10209-16