title: Coupling sol-gel synthesis and microwave-assisted techniques: a new route from amorphous to crystalline high-surface-area aluminium fluoride.
abstract: A non-aqueous sol-gel Al-based fluoride has been subjected to the microwave solvothermal process. The final material depends on the temperature heat treatment used. Three types of material have been prepared: 1) for low temperature heat treatment (90 degrees C) X-ray amorphous alkoxy fluoride was obtained; 2) for the highest temperature used (200 degrees C) the metastable form beta-AlF3 was obtained with a very large surface area of 125 m2 g(-1). The mechanism of the amorphous=crystalline transformation has been rationalised by the occurrence of a decomposition reaction of the gel fluoride induced by the microwave irradiation. 3) Finally, at intermediate temperature (180 degrees C) a multi-component material mixture exhibiting a huge surface area of 525 m2 g(-1) has been obtained and further investigated after mild post-treatment fluorination using F2 gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m2 g(-1). HRTEM revealed that the solid is built from large particles (50 nm) identified as alpha-AlF3, and small ones (10 nm), relative to an unidentified phase. This new high-surface-area material exhibits strong Lewis acidity as revealed by pyridine adsorption and catalytic tests. By comparison with other materials, it has been shown that whatever the composition/structure of the Al-based fluoride materials, the number of strong Lewis acid sites is related to the surface area, highlighting the role of surface reconstruction occurring on a nanoscopic scale on the formation of the strongest Lewis acid sites.
authors.affiliation: Institut de Chimie de la Matière Condensée de Bordeaux-CNRS, Université Bordeaux 1, 87, Avenue du Dr. A. Schweitzer, 33608 Pessac cedex, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Dambournet
authors.forename: Gehan
authors.initials: G
authors.lastname: Eltanamy
authors.forename: Alexandre
authors.initials: A
authors.lastname: Vimont
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Lavalley
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Goupil
authors.forename: Alain
authors.initials: A
authors.lastname: Demourgues
authors.forename: Etienne
authors.initials: E
authors.lastname: Durand
authors.forename: Jérôme
authors.initials: J
authors.lastname: Majimel
authors.forename: Stephan
authors.initials: S
authors.lastname: Rudiger
authors.forename: Erhard
authors.initials: E
authors.lastname: Kemnitz
authors.forename: John M
authors.initials: JM
authors.lastname: Winfield
authors.forename: Alain
authors.initials: A
authors.lastname: Tressaud