Conception de matériaux poreux hiérarchisés synthétisés au départ de précurseurs moléculaires uniques

Abstract

With the decline in reserves of certain raw materials, coupled with the ever growing needs of the population, there is increased pressure on industries to devise novel synthetic processes. The main way to improve the efficiency of those chemicals processes is the design of a new generation of inorganic chemistry based catalysts. The Sol-gel process is one of the most promising technologies permitting the development of an amazing new generation of mixed oxide materials featuring porous organizations at the nanometric scale, a controlled stoichiometry and an excellent homogeneity of the active sites. This class of materials could serve as catalysts for the fine chemistry as well as for petroleum cracking processes. However, the mixed oxide catalytical efficiency is strongly linked to the degree of the active sites dispersion into the silica framework. Usual synthetic methods systematically drive to a phase separation phenomenon, resulting from the different reactivity of the starting independent inorganic precursors used. Synthesized materials are inhomogeneous due to the formation of a poor loaded silica framework and independent metal oxide nanoparticles, characterized by a low catalytical activity. Currently, many efforts are devoted to the improvement of the incorporation of increasing amount of active metal centers into the framework without any phase separation processes. A very promising strategy consists in the use of single molecular source, instead of a mixture of independent inorganic precursors with different reactivities. The aqueous conversions of these single sources allow the construction of materials featuring unmatched homogeneity and totally controlled stoichiometry. This present work aims in the design of a new generation of homogeneous and porous mixed oxides, prepared from single molecular precursors, for some further catalytical applications. This lead first to the conception of porous and homogenenous zirconosilicate materials (Si/Zr ~ 4), followed by the design of macro-mesoporous aluminosilicate solids with high loading of tetrahedral aluminium species (1 < Si/Al < 2), by the controlled (pH adjusting step, use of chelating agents, addition of silica co-reactant,…) polymerisation of selected/synthesized single molecular precursors. These new materials have been intensively characterized by a large panel of techniques (NMR, BET, SEM, TEM,…) in order to highlight their higher chemical homogeneity, and large efforts were dedicated to the fine tuning of the multiscaled porous systems. The mechanisms of spontaneous generations of hierarchical macro-mesoporosities within aluminosilicates samples were carefully studied, notably by optical microscopy. Finally, the ionic exchange and thermal stability properties of these new materials were assessed.

Date of Award	22 Oct 2010
Original language	French
Awarding Institution	University of Namur
Supervisor	BAO LIAN SU (Supervisor), Robert Sporken (President), Alain KRIEF (Jury), Alexandre Leonard (Jury), Paul THIRY (Jury), Rénal BACKOV (Jury) & Clément Sanchez (Jury)