X-ray diffraction and solid-state n.m.r. studies of AEL molecular sieves: Effect of hydration

Applications of27Al multiple quantum magic angle spinning NMR to aluminophosphate molecular sieves

“…1(a) shows the absorptive 27 Al triple quantum MAS (3QMAS) spectrum of the calcined and hydrated form of ALPO 4 -11, 13 which is known to contain five equally populated crystallographic sites. 19 Four aluminum sites (Al 1 -Al 4 ) can be distinguished in the 2D plot of the tetrahedral chemical shift region (υ 2 D 50-20 ppm) and a fifth resonance is observed in the octahedral region (not shown). The position of the centre of gravity of each peak allows for the determination of the chemical shift υ cs and the composite quadrupole coupling constant,…”

“…3(a)] are in very good agreement with the expected 1 : 1 : 1 : 1 : 1 Al site populations. 19 The spectrum in Fig. 3(a) and the analysis results in Fig.…”

Phosphate-Based Zeolites and Molecular Sieves

“…These structures withstand heating at temperatures exceeding 1300 K. Only minor structural changes (typically alterations of the crystallographic space group) are observed upon calcination and rehydration [26,60,62,84,85]. t1 [82] ~ (4 and 6; 2)…”

“…Evolution from tetrahedral to octahedral coordination in molecular sieve frameworks. In the topological description of frameworks, the (x; y ) designation specifies that the framework elements occupy x-connected vertices of the three-dimensional network; oxygen atoms occupy y-connected positions between the x-connected vertices [84] In the A1POrhydrates, water molecules play an important structural role. After the crystallization of AIPO r H3 [33] and VPI-5 [66,86] only water molecules are contained in their micropores.…”

Double rotation27Al NMR in molecular sieves

“…12) and upon hydration, after the extraction of the template, the crystal symmetry changes from body-centred orthorhombic (IMA2) to primitive orthorhombic (PNA21) [31]. The 27AI DOR NMR spectra of the fully hydrated A1PO4-11 at various magnetic fields are given in Fig.…”