HYMUCAT · Innovative organic/inorganic hybrid materials for multifunctional catalysis

Organic-inorganic hybrids are of great interest because they combine the advantage of inorganic solids (high mechanical, thermal and structural stability) and organic molecules (flexibility and functionality). The heterogeneous catalysts are limited in the nature of the active sites and thus the scope of reactions that they can accomplish, whilst the organic molecules can catalyse a larger variety of reactions but suffer from their inability to be recycled. The goal is to use the organic moiety as the active sites and the inorganic solid to provide a way to recover and to recycle the organic sites. The aim of the HYMUCAT project is the synthesis and the characterisation of innovative hybrid porous silicas to produce a multifunctional catalysts having both basic and acid sites. These active sites can act in cascade reactions to provide catalytic activity and selectivity superior to what can be obtained from monofunctional or homogeneous catalysts. Particular attention will be given to the effect of the spatial arrangement of the organic functionalities on the inner surface of porous silica and to the modulation of the strength of the acid and basic sites. Conventional and non-conventional sol-gel processes carried out by a co-condensation will be used to create organic-inorganic hybrids that contain the organic moiety as part of the silica network. Diamines with neighboring atoms and aromatic frames, such as naphthalene, referred as proton sponges, will be used as organic part, they exhibit unusually high basicity constants. Moreover, the weakly acidic silanols, belonging to the silica network, can preactivate the reagents by interaction of the carbonyl groups. This enables the proton sponge in the hybrid to abstract protons with a higher pKa than that of the plain proton sponge. The hybrids will be tested in Knoevenagel condensations and, after the introduction of strong acid sites will be tested in acid/base cascade reactions for the synthesis of fine chemicals.