Study of carbon dioxide diffusion in zeolites with one- and three-dimensional channel networks by MD simulations and FR methods

Abstract

Molecular dynamics (MD) simulations and frequency response (FR) methods have been used to study the diffusion of carbon dioxide in the 10-ring pore zeolites, theta-1 and silicalite-1, which have one- and three-dimensional channel networks, respectively. A good agreement on the diffusivities in silicalite-1 at various coverges has been obtained between MD simulations, FR and PFG NMR methods. The diffusivities in theta-1 calculated from the MD simulations using one molecule were about one order of magnitude faster than when two or more molecules were involved in the simulations. The diffusivities in theta-1 calculated from the MD simulations when more than one molecule was used in the simulations were in reasonable agreement with those determined by the FR method. For CO₂ diffusion in theta-1 the MD simulations showed a transition from normal to single-file diffusion when more than one molecule were involved, while the FR measurements showed a surface resistance at pore entrances due to single-file diffusion, but these effects were not observed in silicalite-1.