Multicomponent diffusion in zeolites and multicomponent surface diffusion

Recent development of theoretical models and experimental results on multicomponent surface diffusion and diffusion in molecular sieves have been briefly summarized. The model development of multicomponent diffusion have been focused on four most attractive approaches which are: single-file approach, Maxwell-Stefan approach, irreversible thermodynamics approach and kinetic approach and with a more detailed model derivations on the last one. A step by step procedures for predicting multicomponent diffusion from single component information have been demonstrated in the examples. Besides, a direct comparison between these four models for co- and counter-diffusion cases are also presented. The single-file and irreversible thermodynamic models have the advantage of being easy to use and having no adjustable parameters. The only information required for this prediction is single component diffusivities. They can be used to predict multicomponent diffusion, especially, at low surface loadings. The kinetic model is capable of predicting multicomponent diffusion between lambda(ij) from 0 to 1. The lambda(ij) is indicative of the level of molecular interactions which can be directly obtained from single component information. Based on these comparisons, it is clear that the kinetic model is superior to the others.