Diffusion in microporous solids

Application of Nuclear Shielding Surfaces to the Fundamental Understanding of Adsorption and Diffusion in Microporous Solids... 

A summary of the major experimental techniques that have been applied to study diffusion in microporous solids is given in Table 1. These can be classified according to the nature of the measurement (transient or steady state), the scale of the measurement (micro, meso or macro) and the type of process (transport or self-diffusion). Additional details with complete references are given in recent reviews [10-12]. 

Measurement of Diffusion in Microporous Solids by Macroscopic Methods... 

Abstract In this chapter the main macroscopic experimental methods for measuring diffusion in microporous solids are reviewed and the advantages and disadvantages of the various techniques are discussed. For several systems experimental measurements have been made by more than one technique, and in Part 3 the results of such comparative studies are reviewed. While in some cases the results show satisfactory consistency, there are also many systems for which the apparent intracrystaUine diffusivities derived from macroscopic measurements are substantially smaUer than the values from microscopic measurements such as PFG NMR. Recent measurements of the transient intracrystalline concentration profiles show that sirnface resistance and intracrystalline barriers are both... 

In this chapter the discussion will be mainly focused on the theories and experimental principles of this gaseous batch system subject to square wave volume perturbations and the applications of the method to determine the diffusivities in microporous solid materials. Some other FR techniques, including both theories and apparatus will also be briefly described. 

Diffusion in microporous solids occurs by activated jumps along the pore channels or across cages within the structure. The rate of diffusion over short distances, of the order of the unit cell repeat, is determined by the frequency of re-orientation of molecules into configurations that permit motion, the strength of interaction with the framework, the distance between adsorption sites and the presence of other molecules in the pores. Structural defects, including... 

Brandani, S., Analysis of the Piezometric Method for the Study of Diffusion in Microporous Solids Isothermal Case, Adsorption, 4, 17 (1998). 

D. M. Ruthven, S. Brandani and M. Eic, Measurement of Diffusion in Microporous Solids by Macroscopic Methods , in Molecular Sieves, eds. H. G. Karge and J. Weitkamp, Springer GmbH, 2008, Vol. 7, Adsorption and Diffusion, p. 45. 

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