DEMOURGUES, Alain; FRANCKE, Loïc; DURAND, Etienne; TRESSAUD, Alain

doi:10.1016/S0022-1139(02)00031-3

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DEMOURGUES, Alain
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

FRANCKE, Loïc
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

DURAND, Etienne
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

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Journal of Fluorine Chemistry. 2002, vol. 114, n° 2, p. 229-236

Elsevier

Résumé en anglais

The stability of Al, Cr and Fe hydroxy-fluorides MF3−x(OH)x which adopt the hexagonal-tungsten-bronze (HTB)-type structure has been discussed by considering the lability of water coordinated to metals from a kinetic point of view. Thus, in the case of Al or Fe compounds, the easy departure of water contributes to the stabilization of fluoride ions as well as isolated hydroxyl groups around the metal, leading to the formation of the HTB structure. The stabilization of the HTB structure with respect to another structural type, the pyrochlore, with a lower density, is governed by this kinetic feature as well as the ability of fluorinated salts used as precursors to attract hydroxyls. Al(III) and Fe(III) represent the strongest acidic cations and the associated HTB-type structure containing isolated OH groups can easily be stabilized. In the case of Cr, a mixture of pyrochlore and HTB-type structure is generally obtained. We have succeeded in preparing, using supercritical medium, new (Fe, Cr) oxyhydroxy-fluorides which exhibit edge-shared octahedra and large 1D tunnels. These compounds can be considered as potential candidates for acid catalysts.< Réduire

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Oxyhydroxy-fluorides

Brønsted/Lewis sites

Acid catalysts

Supercritical medium

FTIR

Hexagonal-tungsten-bronze

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Chemistry and key structural features of oxyhydroxy-fluorides : relationships with the acidic character, thermal stability and surface area

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