Intra-crystallite diffusion

Xenon NMR spectroscopy was used to characterize xenon in Ca, Mg, Ni, Ag, La, Ce and Rb - exchanged Y and X zeolites. We report here some examples concerning the location of these cations and their inter - and - intra crystallite diffusion... 

NMR study of intra- and inter- crystallite diffusion of cations in faujasite zeolites... 

Since the first " Xe NMR study of xenon adsorbed on a zeolite, this technique has been shown to be of interest for the investigation of the distribution and the size of supported metal particles, the quantitative distribution of phases chemisorbed on these particles, the dimensions of the void spaces of zeolites, the detection of structure defects, the location of cations and the effect of electric fields they create [i,2 ]. We report here some typical applications related to the study of intra-and inter-crystallite diffusion of cations in faujasite zeolites. 

A further distinction has to be made between reactions taking place within a molecular crystal and reactions of a molecular crystal A with a molecular crystaT B (see Scheme 2 A and B can also be the same crystal) [7bj. Reactions of the former type, or intra-solid reactions, can be either under topochemical control, depending on the proximity of the reactants, or may imply extensive molecular motion within the crystal lattice. Reactions of the second type, or inter-solid reactions, can either take place on the crystallite surface or require molecular diffusion through the lattice. Inter-solid reactions are often accompanied by formation of eutectics. 

Figure 30 compares the long-range diffusivity of n-butane in a loose bed of NaX zeolite crystallites with that of the same sample after compaction under a pressure of 2.5 MPa. It is found that long-range diffusion in the compacted material is reduced by a factor on the order of 3, which may be attributed to a reduction of both (diminution of the intercrystalline void volume) and (decrease of the intercrystalline pore diameters and hence of the effective mean free path). This experimental result confirms that the contribution of intra-... 

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