High-resolution aluminum-27 NMR of aluminosilicates

The Influence of Si/Al Ratio on the Distribution of OH Groups in Zeolites with MWW Topology

“…Since Al atoms may be located in two distinct pore systems proposed for this zeolite, the presence of the two sets of signals derived from tetrahedral Al is understandable [34]. Lippmaa et al [35] showed that the chemical shifts of tetrahedral Al correlate with average Al-O-Si angles in zeolite frameworks and on this basis the average angles of 152 o and 164 o for the 55 and 48 ppm components were assigned. Keneddy et al [17] then assigned the presence of the 55 ppm peak to the population of T1, T3, T4, T5, T8 sites and the 48 ppm peak to T6 and T7 sites.…”

Synthesis of stoichiometrically controlled reactive aluminosilicate and calcium-aluminosilicate powders

“…This was done manually (using the diffractogram of an empty sample holder) in order to preserve any diffraction intensity from the amorphous content of the powders, however this introduces a small broad hump at lower angles due to differences in diffraction plane height between full and empty sample holders. [46,47], zeolites [48] and mullite [49]. Al(V) and Al(IV) are commonly observed in mullite-like structures in aluminosilicate glasses where charge balancing cations are not in excess [43], and as such any Al existing as Al(V) and Al(VI) in samples A and B is likely to provide some charge balancing to the negative charge associated with tetrahedral Al sites.…”

Procedures for Labeling the High-Resolution Axis of Two-Dimensional MQ-MAS NMR Spectra of Half-Integer Quadrupole Spins

“…Knowing the observed chemical shifts of the center of gravity of a peak in the two dimensions allows us to extract the isotropic chemical shift δ iso CS and the second-order quadrupole shift ω (2)iso −1/2 1/2 of the peak. These two parameters characterize the local symmetry of a crystallographic site in solids [94].…”