Résumé
The synthesis procedure brings about a low threshold value for the surface concentration of Al species and renders MCM-41 a model system for the study of silica-alumina phases. On severely outgassed samples, two types of Lewis sites are present, differing in their protrusion from the surface, as well as Brønsted sites engaged in lateral H-bonding, evidenced by the interaction with NH3 and CO. The conversion of Lewis sites into Brønsted ones by water adsorption shows that the Brønsted species are Si(OH)Al, typical of zeolites, and Si-Al(OH)-Si, found in de aluminated zeolites. The flexibility of the amorphous framework accounts for the differences with zeolitic aluminosilicates.