It was recalled that standard models for single-file diffusion in zeolites assumed that the adsorbate diffusion mechanisms at high and low pore loadings were identical. However, atomistic models of single-file systems had shown that clusters of adsorbed molecules could diffuse via concerted motions that were not available to individual adsorbates. Molecular dynamics simulations were made here of CF4 clusters in AlPO4-5 and of Xe clusters in AlPO4-31. These simulations were used to characterize the diffusion and dissociation mechanisms and rates of these clusters as a function of temperature and cluster size. The molecular dynamics results were also used to parametrize coarse-grained models for adsorbed cluster dynamics. By using kinetic Monte Carlo simulations of these coarse-grained models, pores which contained hundreds of interacting clusters were simulated at μs time-scales. The simulations offered a first opportunity to examine single-file diffusion in models that accurately accounted for the existence of concerted cluster diffusion. The simulation results showed that concerted cluster motions made large contributions to single-file mobilities. Deviations of the calculated single-file mobilities from the results for hard-sphere diffusion were considered, as were the implications of using the latter model to interpret experimental measurements of single-file diffusion.

Influences of Concerted Cluster Diffusion on Single-File Diffusion of CF4 in AlPO4-5 and Xe in AlPO4-31. D.S.Sholl, C.K.Lee: Journal of Chemical Physics, 2000, 112[2], 817-24