Ordering of aluminium and silicon in synthetic faujasites

摘要: The distribution of aluminium and silicon atoms on the tetrahedral sites in synthetic faujasites (zeolites X Y) has been debated for many years. Although framework structure zeolite is known1, detailed Si Al lattice cannot be established by conventional methods, partly because very similar scattering powers rays difficulties obtaining crystals adequate size perfection. Some inferences have, however, made basis four indirect approaches: variation (cubic) parameter as a function content2,3; electrostatic calculations4; change zeolitic acidity successive extraction from framework5–7; kinetics crystallization8. All these approaches have assumed validity ‘Loewenstein's rule’ which forbids occupying neighbouring sites. High-resolution solid-state 29Si NMR (with magic angle spinning) can determine Si, ordering zeolites9–16 . coupled with electron diffraction studies revealed that Loewenstein's rule, generally treated axiomatic, broken Linde A10,13,14 at least three other zeolites where Si/Al nominally unity15. In view its importance an archetypal zeolite, particularly commercially, we re-examined question faujasite. We propose new schemes explain discontinuities unit cell constant composition.