Lithium-7 NMR Studies of Li1−xCoO2 Battery Cathodes

1994 ◽  
Vol 369 ◽  
Author(s):  
B. Ouyang ◽  
X. Cao ◽  
H.W. Lin ◽  
S. Slane ◽  
S. Kostov ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Parent Compound ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Nmr Studies ◽  
Relaxation Measurements ◽  
Angle Spinning

AbstractLithium-deficient cathode materials Li1-xCoO2 where x = 0.1, 0.4 and 0.6 were prepared electrochemically from the stoichiometric parent compound (x = 0.0).The materials were observed to be air-stable, and x-ray diffraction characterization yielded good agreement with the in situ studies of Dahn and co-workers, regarding changes in lattice parameters. In addition to both static and magic angle spinning (MAS) 7Li NMR, measurements, the samples were investigated by EPR and cobalt K-edge NEXAFS. The removal of Li is accompanied by compensating electrons from the Co d-orbitals, asevidenced by both shifts in the NEXAFS peak and the observation of EPR signals due to spins localized on the Co ions. These spins, in turn, result in dramatic 7Li chemical shifts (89 ppm for x = 0.6) and line broadening. Whereas MAS analysis of Li0.9CoO2 indicates two magnetically inequivalent Li sites, the spectra becometoo broad to resolve different sites for higher values of x. Finally NMR linewidth and spinlattice relaxation measurements as a function of temperature suggest a modest increase in Li+ ion mobility for Li-deficient samples as compared to the parent compound.

Continuous Flow Hyper-Polarized 129Xe-Mas Nmr Studies of Microporous Materials.

2003 ◽  
Vol 775 ◽  
Author(s):  
Andrei Nossov ◽  
Flavien Guenneau ◽  
Marie-Anne Springuel-Huet ◽  
Valérie Montouillout ◽  
Jean-Pierre Cognec ◽  
...  
Keyword(s):  
Continuous Flow ◽  
Nmr Spectra ◽  
Magic Angle Spinning ◽  
Mas Nmr ◽  
Magic Angle ◽  
Original Design ◽  
Nmr Studies ◽  
Powder Samples ◽  
Angle Spinning

Summary:A Magic Angle Spinning (MAS) NMR probe has been designed allowing the in-situ measurements of NMR spectra of working catalyst. The probe was built following the original design of M. Hunger [Hunger, 1995 #2]. It allows the magic angle spinning of powder samples up to 3.5 kHz, under gas flowing conditions, and at temperatures up to 573K.

A multinuclear MAS NMR study of the short-range structure of fluorophosphate glass

1992 ◽  
Vol 7 (7) ◽  
pp. 1892-1899 ◽  
Author(s):  
R.K. Brow ◽  
Z.A. Osborne ◽  
R.J. Kirkpatrick
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Spectroscopic Studies ◽  
Magic Angle Spinning ◽  
Mas Nmr ◽  
Magic Angle ◽  
Nmr Studies ◽  
Nmr Study ◽  
Fluorophosphate Glass ◽  
Angle Spinning

We have examined the bonding arrangements in Na–P–O–F and Na–Al–P–O–F glasses using 19F, 27Al, and 31P solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. For the Al-free series of glasses, the 19F NMR spectra are dominated by peaks near +90 ppm, representative of F terminating P-chains. The formation of these bonds has little effect on the 31P chemical shifts, indicating that F preferentially replaces bridging oxygen on the phosphate tetrahedra, consistent with previous NMR studies of crystalline fluorophosphates and other spectroscopic studies of fluorophosphate glass. For the Na–Al–P–O–F glasses, 27Al NMR detects only octahedral Al-sites, the 19F NMR spectra include a second peak near −12 ppm due to F bonded to Al, and the 31P NMR spectra contain signals due to Q1-sites with one or more Al next-nearest neighbors. The relative intensity of the two 19F peaks correlates well with previous spectroscopic studies and shows that a greater fraction of F–P bonds forms when the base glass is remelted in NH4HF2.

scholarly journals Adsorbate-induced Active Site in Zeolite

2020 ◽  
Author(s):  
Guangchao Li ◽  
Christopher Foo ◽  
Xianfeng Yi ◽  
Wei Chen ◽  
Pu Zhao ◽  
...  
Keyword(s):  
Active Sites ◽  
Industrial Applications ◽  
Magic Angle Spinning ◽  
Basic Site ◽  
Magic Angle ◽  
X Ray Diffraction ◽  
Molecular Binding ◽  
Angle Spinning ◽  
Diffuse Reflectance Infrared

Abstract There has been a long debate on how and where active sites are created for molecular adsorption and catalysis in zeolites which underpin many important industrial applications. For example, Lewis acidic site (LAS) and basic site (LBS) are generally believed to be the extra-framework Al species and residue anion (OH−) species formed at fixed crystallographic positions on the zeolite structures after their synthesis. Here, direct experimental observation of adsorbate-induced active sites in silicoaluminophosphate (SAPO) zeolites is for the first time made, which contradicts the traditional view of the fixed active sites in zeolites. Evidence shows that induced Frustrated Lewis pair (three-coordinated framework Al as LAS and SiO(H) as LBS) can be transiently favored for heterolytic molecular binding/reactions of competitive polar adsorbates due to their ineffective orbitals overlap in the rigid framework. High resolution magic-angle spinning solid-state nuclear magnetic resonance (MAS-SSNMR), synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD), in-situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (in-situ DRIFT) and ab initio molecular dynamic (AIMD) demonstrate the presence of only one type of Bronsted acid site (BAS) in the H-SAPO-34, however, when exposed to polar adsorbates such as methanol, the methoxy moiety is shown to be directly coordinated to the framework Al (induced LAS) and the proton to the O(H)-Si (induced LBS) by the induced FLP. Our unprecedented finding opens up a new avenue to understanding of the dynamic establishment of active sites for adsorption or chemical reactions under molecular bombardments to zeolitic structures.

scholarly journals Conversion of sub-µm calcium carbonate (calcite) particles to hollow hydroxyapatite agglomerates in K2HPO4 solutions

2020 ◽  
Vol 9 (1) ◽  
pp. 945-960
Author(s):  
Sun Yanyan ◽  
Wang Guangxin ◽  
Li Wuhui ◽  
Wang Yaming ◽  
Satoshi Hayakawa ◽  
...  
Keyword(s):  
Activation Energy ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Cross Polarization ◽  
X Ray Diffraction ◽  
Nmr Studies ◽  
X Ray ◽  
Order Of Magnitude ◽  
Angle Spinning ◽  
Cp Mas Nmr

AbstractSub-µm CaCO3 (calcite; CC) particles were converted to calcium monohydrogenphosphate dihydrate (DCPD) and hydroxyapatite (HAp) via soaking treatments in K2HPO4 solutions with varied pH (3–12) and concentrations (0.1–1.5 M) at 37°C for up to 10 days. DCPD was derived from the solutions with pH ≤ 6; while hollow HAp was yielded when pH ≥ 7 in assemblies of petal-like crystallites. Results of magic angle spinning (MAS) and cross-polarization magic angle spinning (CP-MAS) NMR studies have shown that the HAp lattice has only PO42− but no HPO42− at B (phosphate) sites. Trace amounts of CO32− have occupied both A (OH) and B (PO4) sites, and H2O is adsorbed on surface crystallites. The primary crystallite size of HAp derived from Scherrer equation increases quickly in a 12 h period and becomes gradually stable afterward. Samples of particles soaked within 3 h in a temperature range of 20–80°C were analyzed by X-ray diffraction. It is shown that the rate constant of 1 M solution is about an order of magnitude greater than that of 0.1 M solution and the apparent activation energy is 33 kJ/mol. In this work, the conversion of CC to HAp can be quantitatively controlled to solve the problem of slow degradation of HAp.

13C-LABELLING FOR NMR STUDIES OF SOILS: CPMAS NMR OBSERVATION OF 13C-ACETATE TRANSFORMATION IN A MINERAL SOIL

1983 ◽  
Vol 63 (3) ◽  
pp. 495-500 ◽  
Author(s):  
CAROLINE M. PRESTON ◽  
J. A. RIPMEESTER
Keyword(s):  
Mineral Soil ◽  
Size Fraction ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Line Broadening ◽  
Difference Spectra ◽  
Nmr Studies ◽  
Fine Size ◽  
Angle Spinning ◽  
C Nmr

Few nmr studies with whole soil have been successfully attempted. Solid-state 13C nmr spectra were obtained for Bainsville clay loam an orthic humic gleysol with 3% carbon, using the CPMAS technique (cross-polarization magic-angle spinning). Results for the whole soil were limited by poor signal/noise and lack of resolution, possibly due to line-broadening by iron. Better results were obtained by employing a < 50 μm fine-size fraction, and difference spectra techniques, allowing observation of added 13C-labelled acetate, and its transformation during incubation. Key words: 13C nmr, CPMAS, labelling, soil

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