Crystalline Aluminum Hydroxide Fluorides AlFx(OH)3−x·H2O: Structural Insights from 1H and 2H Solid State NMR and Vibrational Spectroscopy

Scholz, Gudrun; Brehme, Sven; König, R.; Heidemann, D.; Kemnitz, Erhard

doi:10.1021/jp1023857

Cited by 22 publications

(12 citation statements)

References 18 publications

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“…F and OH groups were statistically distributed at the corners of the octahedrons, while water molecules, present in the channels and on the surface of aluminum hydroxide fluorides, were hydrogen bonded with the AlF x O 6-x network. Also, a minor amount of β-AlF 3 was present in the fresh AF solid [50,51,52].…”

Section: Resultsmentioning

confidence: 99%

Towards a Rational Design of a Continuous-Flow Method for the Acetalization of Crude Glycerol: Scope and Limitations of Commercial Amberlyst 36 and AlF3·3H2O as Model Catalysts

et al. 2016

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Abstract:The acetalization of six different types of glycerol including pure, wet, and crude-like grade compounds of compositions simulating those of crude glycerols produced by the biodiesel manufacture, was carried out with two model ketones such as acetone and 2-butanone. The reaction was investigated under continuous-flow (CF) conditions through a comparative analysis of an already known acetalization catalyst such as Amberlyst 36 (A36), and aluminum fluoride three hydrate (AlF 3¨3 H 2 O, AF) whose use was never previously reported for the synthesis of acetals. At 10 bar and 25˝C, A36 was a highly active catalyst allowing good-to-excellent conversion (85%-97%) and selectivity (99%) when either pure or wet glycerol was used as a reagent. This catalyst however, proved unsuitable for the CF acetalization of crude-like glycerol (CG) since it severely and irreversibly deactivated in a few hours by the presence of low amounts of NaCl (2.5 wt %) which is a typical inorganic impurity of raw glycerol from the biorefinery. Higher temperature and pressure (up to 100˝C and 30 bar) were not successful to improve the outcome. By contrast, at 10 bar and 100˝C, AF catalyzed the acetalization of CG with both acetone and 2-butanone, yielding stable conversion and productivity up to 78% and 5.6 h´1, respectively. A XRD analysis of fresh and used catalysts proved that the active phase was a solid solution (SS) of formula Al 2 [F 1-x (OH) x ] 6 (H 2 O) y present as a component of the investigated commercial AF sample. A hypothesis to explain the role of such SS phase was then formulated based on the Brønsted acidity of OH groups of the solid framework. Overall, the AF catalyst allowed not only a straightforward upgrading of CG to acetals, but also a more cost-efficient protocol avoiding the expensive refining of raw glycerol itself.

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Section: Resultsmentioning

confidence: 99%

Towards a Rational Design of a Continuous-Flow Method for the Acetalization of Crude Glycerol: Scope and Limitations of Commercial Amberlyst 36 and AlF3·3H2O as Model Catalysts

et al. 2016

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“…[62][63][64][65] In the course of intensive mechanistic investigations that are reviewed in ref. 9 and 10, the presence of intermediately formed metal alkoxide fluorides was evidenced by both MAS-NMR 22,[66][67][68][69][70][71][72] and single crystal structure determination. 73 This will be exemplarily shown for the aluminium fluoride system.…”

Section: Binary Metal Hydroxide Fluoridesmentioning

confidence: 99%

Nanoscale metal fluorides: a new class of heterogeneous catalysts

Kemnitz

2015

Catal. Sci. Technol.

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“…A new signal occurs at 3646 cm −1 for ν(OH), which can be assigned to bridging Al-OH groups or bridging Al-F groups coordinating water. 11 In Fig. 4c the FT-IR spectrum of the aluminium trifluoroacetate fluoride (3) synthesized by the alkoxide free synthesis is presented.…”

Section: Mas Nmr Measurementsmentioning

confidence: 99%

Preparation and stabilization of aluminium trifluoroacetate fluoride sols for optical coatings

et al. 2012

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For the first time, aluminium fluorides in liquid phase are available for optical applications. By modifying the conditions of the fluorolytic sol-gel synthesis of aluminium fluorides transparent sols with low viscosities were obtained. These sols consist mainly of small oligomeric or cluster units of aluminium fluoride which are not measurable by DLS, WAXS, SAXS and show unusual narrow signals in solid state NMR. Isolated particles with diameters up to five nanometers can be identified by TEM measurements and allow the use of their sols in optical and anti reflecting coatings. The sol particles were modified by trifluoroacetic acid to prevent agglomeration, and as a result, the obtained xerogels can be re-dispersed transparently in organic solvents.

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Crystalline Aluminum Hydroxide Fluorides AlF_x(OH)_3−x·H₂O: Structural Insights from ¹H and ²H Solid State NMR and Vibrational Spectroscopy

Cited by 22 publications

References 18 publications

Towards a Rational Design of a Continuous-Flow Method for the Acetalization of Crude Glycerol: Scope and Limitations of Commercial Amberlyst 36 and AlF3·3H2O as Model Catalysts

Towards a Rational Design of a Continuous-Flow Method for the Acetalization of Crude Glycerol: Scope and Limitations of Commercial Amberlyst 36 and AlF3·3H2O as Model Catalysts

Nanoscale metal fluorides: a new class of heterogeneous catalysts

Preparation and stabilization of aluminium trifluoroacetate fluoride sols for optical coatings

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