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Issue 21, 2008
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Structural investigations and acidic properties of high surface area pyrochlore aluminium hydroxyfluoride

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Abstract

High surface area aluminium hydroxyfluoride exhibiting the pyrochlore-type structure has been synthesized using microwave hydrothermal process. The optimization of the crystallite size and surface area of the material has been performed by varying some synthesis parameters, i.e. the nature of the aluminium precursor, the choice of solvents and the addition of a small amount of ether. The as-prepared solid contains nanosized particles as calculated by XRD (average particle size: 12 nm) leading to a surface area around 140 m2 g−1. These results have been confirmed by TEM observations. The framework is built of AlF6−x(OH)x species which have been characterized and quantified by high field 27Al NMR. A random distribution of F atoms and OH groups is evidenced to occur on the 48f sites. Inside the channels, water molecules interact with the framework by hydrogen bonding either with fluoride ions or OH groups present in their vicinity. The use of probe molecules has shown that the pyrochlore exhibits a Lewis acidity lying between that of γ-Al2O3 and that of the strong Lewis acid β-AlF3 adopting the hexagonal tungsten bronze form. Surface OH groups have been characterized by IR spectroscopy and exhibit weak Brønsted acidity.

Graphical abstract: Structural investigations and acidic properties of high surface area pyrochlore aluminium hydroxyfluoride

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Publication details

The article was received on 06 Dec 2007, accepted on 12 Feb 2008 and first published on 25 Mar 2008


Article type: Paper
DOI: 10.1039/B718856K
Citation: J. Mater. Chem., 2008,18, 2483-2492
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    Structural investigations and acidic properties of high surface area pyrochlore aluminium hydroxyfluoride

    D. Dambournet, A. Demourgues, C. Martineau, E. Durand, J. Majimel, A. Vimont, H. Leclerc, J.-C. Lavalley, M. Daturi, C. Legein, J.-Y. Buzaré, F. Fayon and A. Tressaud, J. Mater. Chem., 2008, 18, 2483
    DOI: 10.1039/B718856K

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