Journal
CHEMPHYSCHEM
Volume 10, Issue 14, Pages 2429-2433Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.200900279
Keywords
diffusion; electron microscopy; neutron scattering; NMR spectrocopy; zeolites
Funding
- DFG
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By applying pulsed-field gradient nuclear magnetic resonance (PFG NMR) in comparison to quasi-elastic neutron scattering (QENS), we sense by measurement of the diffusion of n-octane on different length scales, transport resistances in faujasite type X (which is isostructural with type Y and differs by the lower Si/Al ratio only) with mutual distances of less than 300 nm. Direct observation of the real structure of zeolite X by transmission electron microscopy identifies them as stacking faults of mirror-twin type on (111)-type planes of the cubic d framework. Thus, direct experimental proof is given that, in general, nanoporous host systems such as zeolite crystals cannot be considered as a mere arrangement of cavities. It is rather the presence of structural defects that dominates their properties as soon as transport phenomena with practical relevance, including chemical conversion by heterogeneous catalysis and chemical separation by molecular sieving and selective adsorption, become relevant.
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