The need for operando modelling of ²⁷Al NMR in zeolites: the effect of temperature, topology and water

Abstract

Solid state (ss-) 27Al NMR is one of the most valuable tools for experimental characterization of zeolites, owing to its high sensitivity and the detailed structural information which can be...

Simultaneous Control of Aluminum Atoms and Defects in the MOR Zeolite Framework by Postsynthetic Treatments

“…The attachment of H to the O b for charge neutralization significantly reduced the spherical symmetry of the electric field of 27 Al. This trend is consistent with GIPAW calculations in previous studies . These Al sites may correspond to the peaks ranging from 20 to 50 ppm observed in the 27 Al MAS NMR spectrum of steam-treated MOR, which was missing in the 27 Al 3QMAS NMR spectrum.…”

“…The chemical shifts reported in the previous literature for the four Tn sites ranged from 49.7 to 56 ppm, varying by about 2–3 ppm depending on the cell size. In contrast, the chemical shift for the charged D0 model in this study ranged from 46.3 to 49.4 ppm.…”

“…We utilized four aluminosilicate crystals with well-defined crystal structures: andalusite, kyanite, sillimanite, and α-alumina. , A linear relationship between GIPAW results and experimental values was derived from these references, as shown in our previous work δ exp = 1.0302 σ cal + 559.20 where δ exp and σ cal are the experimental and GIPAW-calculated chemical shifts, respectively. In the previous study, aluminum acetylacetonate and three hydrated zeolites in acidic form were used as references, leading to a linear relationship δ exp = 1.116 σ cal + 609.72 Although a linear relationship was established in both studies, the validity of the reference line in the previous study is uncertain because of only four data points. Moreover, the use of hydrated zeolites as a reference poses problems.…”

“…82,83 A linear relationship between GIPAW results and experimental values was derived from these references, as shown in our previous work 84 where δ exp and σ cal are the experimental and GIPAW-calculated chemical shifts, respectively. In the previous study, 101 aluminum acetylacetonate and three hydrated zeolites in acidic form were used as references, leading to a linear relationship…”

Synthetic Placement of Active Sites in MFI Zeolites for Selective Toluene Methylation to para-Xylene

“…Solid-state 27 Al NMR was used to probe the distributions of tetrahedrally coordinated Al in the frameworks of MFI synthesized with TPA + and nonconventional OSDAs. 27 Al MAS NMR spectra showed qualitative differences in spectral features that support the presence of different framework Al distributions among these samples (additional details in Section S5.12, Supporting Information); however, given the well-documented challenges in resolving Al T-site assignments in the low-symmetry MFI framework using NMR, − we turned to DFT to assess plausible locations of occluded SDAs and their influence on the energetics of siting Al among different T-sites in MFI.…”