Coupling sol-gel synthesis and microwave-assisted techniques: A new route from amorphous to crystalline high-surface-area aluminium fluoride

Dambournet, D. et al. (2008) Coupling sol-gel synthesis and microwave-assisted techniques: A new route from amorphous to crystalline high-surface-area aluminium fluoride. Chemistry: A European Journal, 14(20), pp. 6205-6212. (doi: 10.1002/chem.200701831)

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 m(2)g(-1). ne 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 m(2)g(-1) has been obtained and further investigated after mild post-treatment fluorination using F-2 gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m(2)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.

• Item Type: Articles
• Keywords: ACID ADSORPTION BETA-ALF3 CRYSTALLINE Decomposition FLUORIDES GALLIUM GAS high surface area HYDROXYFLUORIDES Lewis acidity Lewis acids LOW-TEMPERATURE MECHANISM METAL FLUORIDES microwave solvothermal processes NANOSTRUCTURES OXIDE PARTICLES PHASE Pyridine ROUTE sol-gel processes SOL-GEL SYNTHESIS SURFACE SURFACE-AREA TEMPERATURE TRANSFORMATION X-RAY
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Winfield, Professor John
• Authors: Dambournet, D., Eltanamy, G., Vimont, A., Lavalley, J. C., Goupil, J. M., Demourgues, A., Durand, E., Majimel, J., Rudiger, S., Kemnitz, E., Winfield, J. M., and Tressaud, A.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Chemistry: A European Journal
• ISSN: 0947-6539
• ISSN (Online): 1521-3765