ZSM‑5 Zeolite: Complete Al Bond Connectivity and Implications on Structure Formation from Solid-State NMR and Quantum Chemistry Calculations

Al site distribution in the structurally complex and industrially important ZSM-5 zeolite is determined by studying the spectroscopic response of Al­(OSi)₄ units and using a self-consistent combination of up-to-date solid-state NMR correlations (²⁹Si–²⁷Al and ¹H–²⁷Al <i>D</i>-HMQC) and quantum chemistry methods (DFT-D). To unravel the driving forces behind specific Al sitting positions, our approach focuses on ZSM-5 containing its more efficient OSDA, tetrapropylammonium

Temperature-Dependent 4‑, 5- and 6‑Fold Coordination of Aluminum in MOCVD-Grown Amorphous Alumina Films: A Very High Field ²⁷Al-NMR study

The only easy way to prepare amorphous alumina is via thin film deposition. For this reason, the disorder in amorphous alumina has not yet been fully investigated. We have used very high-field (20 T) solid state ²⁷Al NMR spectroscopy to analyze the structural modifications of amorphous alumina thin films with deposition temperature (<i>T</i>_d). The films were deposited by metalorganic chemical vapor deposition in the <i>T</i>_d range of 360–720 °C. Depending on <i>T</i>_d, film composition is either AlO_1+<i>x</i>(OH)_{1–2<i>x</i>} (0 ≤ <i>x</i> ≤ 0.5) or Al₂O₃. From ²⁷Al 1D magic angle spinning (MAS) and 2D multiple-quantum magic angle spinning (MQMAS) NMR analyses, the films grown between 360 and 600 °C contain between 38 and 43 atom % of 5-fold coordinated aluminum sites (^[5]Al). The percentages of ^[6]Al and ^[4]Al sites vary spectacularly, reaching their respective minimum (5 atom %) and maximum (54 atom %) around 515 °C. The analysis of a very thin film (85 nm) of Al₂O₃ reveals the presence of metallic aluminum at the interface with the substrate and suggests that the respective percentages of ^[<i>n</i>]Al sites slightly differ from those in thicker films. The observed <i>T</i>_d dependence of amorphous alumina structure can be correlated with that of film properties previously reported, namely, Young’s modulus, hardness, and corrosion protection

Probing Disorder in Al-ZSM‑5 Zeolites by ¹⁴N NMR Spectroscopy

¹⁴N solid-state NMR spectroscopy is used to investigate and quantify the nanometer scale disorder promoted by Al/Si substitution in ZSM-5 zeolites. After a preliminary characterization by SEM, XRD, and multinuclear (¹H, ¹³C, ¹⁹F, ²⁷Al, ²⁹Si) solid-state NMR, the ¹⁴N MAS NMR spectra of a series of as-synthesized ZSM-5 zeolites containing various amounts of Al are analyzed. The ¹⁴N spinning sideband patterns are shown to evolve with the Si/Al ratio. The modeling of the NMR spectra allows one to estimate the local disorder arising from the Al site distribution within the tetrahedral sites of the zeolites, the variations of F locations, and the presence of silanol defects. The influence of the zeolite framework modifications due to Al/Si substitution on ¹⁴N NMR parameters is discussed on the basis of the results obtained with the Density Functional Theory periodic quantum chemical calculations augmented with an empirical London dispersion term. Analysis of the results highlighted the influence of CNC angle variations on the ¹⁴N quadrupole coupling constant distributions

Solid-State NMR of the Family of Positive Electrode Materials Li₂Ru_1–<i>y</i>Sn_<i>y</i>O₃ for Lithium-Ion Batteries

The possibilities offered by ex situ and in situ operando ⁷Li solid-state nuclear magnetic resonance (NMR) are explored for the Li₂Ru_1–<i>y</i>Sn_<i>y</i>O₃ family (0 < <i>y</i> < 1), shown previously to display cationic and anionic redox activity when used as a positive electrode for Li ion batteries. Ex situ NMR spectroscopic studies indicate a nonrandom Sn/Ru substitution in the family. In the first charge, an increased metallicity at 4 V is deduced from the NMR spectra. Surprisingly, no striking difference is observed at 4.6 V compared to the pristine electrode, although the electronic structure is expected to be very different and the local cation environment to be distorted. For in situ operando measurements, we designed a new electrochemical cell that is compatible with NMR spectroscopy and one-dimensional magnetic resonance imaging (MRI). These operando measurements validate the ex situ observations and indicate that the environment formed at 4 V is specific of the initial charge and that there is little, if no, electrolyte decomposition, even at 4.6 V. This is another attractive feature of these compounds

Solid-State NMR of the Family of Positive Electrode Materials Li₂Ru_1–<i>y</i>Sn_<i>y</i>O₃ for Lithium-Ion Batteries

The possibilities offered by ex situ and in situ operando ⁷Li solid-state nuclear magnetic resonance (NMR) are explored for the Li₂Ru_1–<i>y</i>Sn_<i>y</i>O₃ family (0 < <i>y</i> < 1), shown previously to display cationic and anionic redox activity when used as a positive electrode for Li ion batteries. Ex situ NMR spectroscopic studies indicate a nonrandom Sn/Ru substitution in the family. In the first charge, an increased metallicity at 4 V is deduced from the NMR spectra. Surprisingly, no striking difference is observed at 4.6 V compared to the pristine electrode, although the electronic structure is expected to be very different and the local cation environment to be distorted. For in situ operando measurements, we designed a new electrochemical cell that is compatible with NMR spectroscopy and one-dimensional magnetic resonance imaging (MRI). These operando measurements validate the ex situ observations and indicate that the environment formed at 4 V is specific of the initial charge and that there is little, if no, electrolyte decomposition, even at 4.6 V. This is another attractive feature of these compounds