A multiple-field 23Na NMR study of sodium species in porous carbons

Freitas, Jair C. C.; Schettino, Miguel A.; Emmerich, Francisco G.; Wong, Alan; Smith, Mark E.

doi:10.1016/j.ssnmr.2007.10.002

Cited by 13 publications

(3 citation statements)

References 36 publications

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“…Coal samples K1 and K2 were further analyzed by solidstate 27 Al nuclear magnetic resonance ( 27 Al MAS NMR). Using this method, aluminum complexes with organic ligands in coal organic mass were identified according to (Straka 2016) and with regard to the works (Howarth et al 1987;Kirkpatrick 1988;Burchil et al 1991;Kanehashi and Saito 2004;Smith and van Eck 1999;MacKenzie and Smith 2002;Freitas et al 2007). The solid-state 27 Al MAS NMR spectra were recorded using a Bruker Avance 500 WB/US NMR spectrometer (Karlsruhe, Germany) with 4-mm double-resonance probe heads at the MAS rate of x r / 2p = 11 kHz.…”

Section: Analytical Proceduresmentioning

confidence: 99%

Coalification and coal alteration under mild thermal conditions

Straka

Sýkorová

2018

Int J Coal Sci Technol

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Coalification temperatures are often considered to be approximately 100-170°C for bituminous coal and 170-275°C for anthracite. However, our micropetrographic observations, solid state 27 Al magic-angle spinning nuclear magnetic resonance measurements, interpretation of d 13 C values for whewellite in pelosiderite concretions from Carboniferous sediments, and assessment of whewellite thermal stability show that coalification temperatures can be significantly lower. Also the temperatures of coal alteration may be substantially lower than is stated. Ordinarily, hightemperature alteration is reported, but microthermometric measurements of fluids temperatures and micropetrographic observations show that the coal alteration can take place at low temperatures. For this reason, coals from the Kladno-Rakovník Basin, part of Late Paleozoic continental basins of the Czech Republic, were analyzed. Regarding coalification, micropetrographic characterizations of unaltered coals, the presence of thermally unstable Al complexes in the coal organic mass documented using 27 Al MAS NMR method, and proven occurrence of whewellite in pelosiderite concretions suggest a lower coalification temperature, max.~70°C. Regarding coal alteration, micropetrographic observations revealed (a) the weaker intensity of fluorescence of liptinite, (b) mylonitic structures and microbreccia with carbonate fluid penetration, and (c) high oxygen content in coals (37-38 wt.%). These phenomena are typical for thermal and oxidative alteration of coal. As the temperature of carbonate fluids inferred from fluid inclusion analysis was evaluated as * 100-113°C, the temperature of coal alteration was suggested as * 113°C; the alteration was caused by hot hydrothermal fluids.

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Section: Analytical Proceduresmentioning

confidence: 99%

Coalification and coal alteration under mild thermal conditions

Straka

Sýkorová

2018

Int J Coal Sci Technol

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“…Isotropic peaks are evident at −9 ppm and +4 ppm (no metallic 23 Na resonances are observed), and there is a broad unresolved feature underneath the peaks. Freitas et al 25 measured the 23 Na resonance within the range of 0 to −30 ppm for Na + infused carbon (with a much smaller average pore size than that reported here). This Na site was characterized by a large quadrupole coupling constant of about 1.2 to 1.8 MHz.…”

Section: Bet Area Total Porousmentioning

confidence: 44%

NaAlH₄Nanoconfinement in a Mesoporous Carbon for Application in Lithium Ion Batteries

Silvestri

Paolone

Cirrincione

et al. 2017

J. Electrochem. Soc.

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Alanates have recently attracted attention as new anodic materials for lithium ion batteries. The electrochemical activity of sodium alanate has been already reported and the conversion mechanism explained. Through a complex conversion reaction, this compound is able to develop almost all the theoretical capacity, achieving more than 1700 mAh/g upon first discharge with an efficiency of 70%. Nevertheless alanate undergoes to capacity fade in few cycles. This is mainly due to the severe structural reorganization following the conversion reaction, that results in electrode pulverization and loss of electric contact. Here, we present a nanocomposite material consisting of NaAlH4 confined in the nanoporous of a carbon matrix able to mitigate the effect of volume expansion and improve the cyclability. Specifically, the nanocomposite has been studied in terms of structure, morphology and hydrogen content by the means of Infrared Spectroscopy, solid state NMR, electronic microscopy and thermal analysis. Finally, its performance in lithium cells is presented.

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“…Second and based on the previously mentioned papers, ,− we will assign the various precursor and HS-AlF 3 NMR signalspuzzled out of the featureless NMR spectrato specific structures that exist in these samples. Magic angle sample spinning (MAS) and triple quantum experiments (3QMAS) − at different magnetic fields (14.1−19.9 T) have been carried out to reduce line broadenings due to both distributions of isotropic chemical shifts and second order quadrupolar interactions − that hamper an unambiguous assignment of aluminum sites present in these materials.…”

Section: Introductionmentioning

confidence: 99%

Access to Local Structures of HS-AlF₃ and Its Precursor Determined by High-Resolution Solid-State NMR

et al. 2009

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High-surface aluminum fluoride (HS-AlF3) is an interesting catalytic material and possesses high surface areas compared to crystalline aluminum fluorides and strong Lewis acidity. HS-AlF3 and its precursor aluminum isopropoxide fluoride are X-ray amorphous, which makes precise structural elucidations very difficult, which is, in turn, the prerequisite for understanding its extraordinary properties. For this reason 27Al NMR using magic angle sample spinning (MAS) and multiple quantum NMR (MQMAS) has been carried out at different magnetic field strengths up to 19.9 T in order to gain maximum information about the various AlF6−x O x (x = 0, 1, 2, ...) octahedra present in the precursor and HS-AlF3 structure. The 27Al NMR spectra are almost featureless irrespective of the applied B 0 fields because of distributions of isotropic chemical shifts and second order quadrupolar effects. Nevertheless, it was possible to verify the presence of four different octahedra in the materials following the results of earlier investigations of the sol−gel of these HS-AlF3 samples. Different oxygen-containing AlF5O and AlF4O2 are found in the precursor structure, whereas AlF6 sites determine the HS-AlF3 structure besides residual AlF5O and AlF4O2 octahedra after postfluorination of the precursor.

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A multiple-field 23Na NMR study of sodium species in porous carbons

Cited by 13 publications

References 36 publications

Coalification and coal alteration under mild thermal conditions

Coalification and coal alteration under mild thermal conditions

NaAlH₄Nanoconfinement in a Mesoporous Carbon for Application in Lithium Ion Batteries

Access to Local Structures of HS-AlF₃ and Its Precursor Determined by High-Resolution Solid-State NMR

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A multiple-field 23Na NMR study of sodium species in porous carbons

Cited by 13 publications

References 36 publications

Coalification and coal alteration under mild thermal conditions

Coalification and coal alteration under mild thermal conditions

NaAlH4Nanoconfinement in a Mesoporous Carbon for Application in Lithium Ion Batteries

Access to Local Structures of HS-AlF3 and Its Precursor Determined by High-Resolution Solid-State NMR

Contact Info

Product

Resources

About

NaAlH₄Nanoconfinement in a Mesoporous Carbon for Application in Lithium Ion Batteries

Access to Local Structures of HS-AlF₃ and Its Precursor Determined by High-Resolution Solid-State NMR