Diffusion pathways of benzene, toluene and p-xylene in MFI |
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Authors: | OC Gobin SJ Reitmeier A Jentys JA Lercher |
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Affiliation: | aDepartment of Chemistry, Technische Universität München, Lichtenbergstraße 4, D-85748 Garching, Germany |
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Abstract: | The diffusion of alkyl-substituted aromatic molecules in H-ZSM-5 was investigated by means of the frequency response method decoupling particle size effects and intracrystalline diffusion. For zeolite crystals above 5 μm average diameter, the transport in the zeolite pores exerts a significant effect on the overall transport causing anisotropic diffusion as the aspect ratio of the aromatic molecules increases. Diffusion of benzene is nearly isotropic, while p-xylene shows marked differences between the diffusive processes in the straight and sinusoidal channel system of ZSM-5. The isotropic diffusion of benzene is rationalized on the basis of its ability to reorient between the two channel systems without major hindrances. For p-xylene, switching between the channels is only possible by energetically unfavorable rotational motions leading to a low probability for changing between both channel systems. |
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Keywords: | Frequency response Particle size distribution MFI-type zeolites Aromatics Intra-crystalline diffusion |
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