Oxygen coordination of aluminum cations in dehydrated AlPW12O40 investigated by solid-state NMR spectroscopy

Solid-state nuclear magnetic resonance investigations of the nature, property, and activity of acid sites on solid catalysts

“…This finding indicates that dehydroxylation of AlPW 12 O 40 should change the oxygen coordination of the extra-framework aluminum cations in this material. In agreement with this assumption, variable-field 27 Al MAS NMR studies of dehydrated AlPW 12 O 40 evidenced that the dehydroxylation of AlOH groups occurring upon increasing the dehydration temperature from 473 to 573 K is accompanied by a decrease of the number of octahedrally coordinated aluminum species and a corresponding increase of the number of pentacoordinated aluminum species [143].…”

Ethanol conversion over cesium-doped mono- and bi-cationic aluminum and gallium H3PW12O40 salts

“…This is probable the result of metal cations ability to promote formation of additional protons which may be the source of acidity in GaPW and AlPW samples. According to the literature [39] the protons which are formed during water dissociation (Reaction (1)) should be easier create by Ga 3+ ions than Al 3+ one, due to the fact that gallium has higher electronegativity (3.23) than aluminum (1.94) according to Sanderson's scale [40]. Both IR (Fig.…”

Effect of Dehydration on the Local Structure of Framework Aluminum Atoms in Mixed Linker MIL-53(Al) Materials Studied by Solid-State NMR Spectroscopy

“…This finding demonstrates that the functionalization of MIL-53(Al) by amine groups induced the decrease of the C Q value by ∼1 MHz. A smaller C Q value indicates a more isotropic charge distribution in the local structure of the resonating quadrupolar 27 Al nuclei . Moreover, the very small asymmetry parameter of ∼0.1 (see Table ) used to simulate both the quadrupolar patterns QB and QA is a hint to a high local symmetry for aluminum atoms in the above-mentioned nonequivalent local structures.…”

“…A smaller C Q value indicates a more isotropic charge distribution in the local structure of the resonating quadrupolar 27 Al nuclei. 25 Moreover, the very small asymmetry parameter of ∼0.1 (see Table 2) used to simulate both the quadrupolar patterns QB and QA is a hint to a high local symmetry for aluminum atoms in the above-mentioned nonequivalent local structures. The relative intensity of 15% corresponding to the molar fraction of framework aluminum atoms coordinated to organic ABDC linkers is very similar to the molar fraction of 10% ABDC utilized as organic linkers in the synthesis mixture.…”