27Al MAS n.m.r. evidence for the reversible transformation of the coordination of aluminum in dealuminated mazzite

Steaming Drived Chemical Interactions of ZnClx with Y Zeolite Framework, Its Regulation to Dealumination/Silicon-Healing as well as Enhanced Availability of Brønsted Acidity

“…Therefore, we deduce that [ZnCl] + and [ZnOH] + bonded on the zeolite framework give rise to some partially dealuminated framework. Also, the peak at 60 ppm tetrahedrally coordinated FAl splits out a shoulder peak at near 54 ppm, especially in the final sample, which has also been attributed to tetrahedrally coordinated FAl that is less stable than the aluminum site at 60 ppm. − There is also a broad peak at 30–50 ppm attributed to penta-coordinated or distorted tetrahedral EFAl . Based on the results of peaks fitting and deconvolution (Figure c,d, Table ), it is indicated that steaming treatment without ZnCl 2 leads to continuous removal of FAl at 60 ppm and a growing amount of the less stable FAl at 54 ppm.…”

Migration of Framework Aluminum and Tunable Acidity in Y Zeolite by Post-treatment

“…Since the steaming treatment started from NH 4 Y samples and they could be converted into HY samples at high temperatures, thus, the corresponding NH 4 Y and HY samples derived from different parent NaY zeolites were analyzed by 27 Al NMR spectra to study their Al states. Generally, for zeolite samples, the peak at around 0 ppm is attributed to octahedral Al­(VI), the broad peak in the range of 20–40 ppm is attributed to Al­(V), the peak at 55 ppm is attributed to tetrahedral Al­(IVb) existing in distorted structure, such as (SiO) 3 AlOH, and the peak at 60 ppm is due to Al­(IVa) species that are intact in the zeolite framework connected with four bridging oxygen bonds. , The octahedral Al­(VI) can be further divided into two kinds: the broad peak is assigned to Al­(VIa), while the other sharp peak is ascribed to Al­(VIb), which are reversible octahedral Al species and can become tetrahedral Al in the presence of extra-framework cations (e.g., Na + and NH 4 + ) . Al­(V) and Al­(VI) are generally regarded as EFAL species; nevertheless, it is essential to distinguish the concept of EFAL from framework-associated Al .…”

Influence of Dealumination by Acetylacetone on Acidity and Activity of Amorphous Silica‐Aluminas

“…Dealumination process is rather complicated, as many thermodynamic or kinetic factors will affect it significantly depending on the experimental conditions . Dealumination can be achieved by steaming, leaching with acids, treatment with chelating agents such as hexafluorosilicate, ammonium hydrogen difluoride (NH 4 HF 2 ), ethylenediamine tetracetic acid, acetylacetone− and many others. Acetylacetone as a bidentate and nonacidic ligand is a suitable agent for mild dealumination leading to the extraction of “loosely bond” aluminum atoms in zeolites .…”