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Préparation et caractérisation d'hydroxy- et d'oxyhy-droxyfluorures d'aluminium, de fer ou de chrome. Corrélation entre la composition/structure, la stabilité thermique et les propriétés acides.

Abstract : The aim of this work was to prepare fluorinated HTB- or hollandite-type compounds in which anions such as OH- or O2- are substituting fluorine. On a structural point of view, frameworks exhibit tunnels along one direction. The competition between fluorination and hydroxylation has been studied on the basis of the crystal structure and FTIR investigations in order to explain the thermal stability of these compounds. Finally, surface acidity, which is different than in the case of oxides, has been investigated. The aim of these studies was to propose a solid state chemistry approach in order to explain the morphology, thermal stability and acidic properties of hydroxy- and oxyhydroxyfluorides which exhibit an open structure. This work also shows the influence of cation and the route of synthesis. Then it will be described the preparation and a characterization of new hollandite-type iron and iron/chromium oxyhydroxyfluorides has been studied. Finally, on the basis of neutron diffraction experiments, the two frameworks HTB and hollandite led to show the effect of the structure on these physico-chemical properties. Our results have shown the key role of the cations, anions and crystal structure in the different properties and particularly the importance of a new parameter, /r, which depends on the nature of the cation and which characterizes both the Lewis acid sites strength and the thermal stability. Inner water molecules and the amount and nature of hydroxyl groups are key elements which influence the thermal stability and acidic properties of the final material.
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Submitted on : Monday, October 13, 2003 - 10:01:27 AM
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Loïc Francke. Préparation et caractérisation d'hydroxy- et d'oxyhy-droxyfluorures d'aluminium, de fer ou de chrome. Corrélation entre la composition/structure, la stabilité thermique et les propriétés acides.. Catalyse. Université Sciences et Technologies - Bordeaux I, 2002. Français. ⟨tel-00003522⟩

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