Mesoscopic interaction between surfactant and silica-alumina during the direct synthesis of AlSBA-15 mesoporous molecular sieves: double resonance NMR study and consequences on structural properties.

摘要

Aluminum-incorporated SBA-15 mesoporous materials have been obtainedrnby direct synthesis. The surfactant – aluminosilicate interaction duringrnsynthesis was studied by double resonance NMR and confronted with thernstructural properties of the materials obtained after calcinations. TRAPDORrnexperiments firmly established a strong interaction between segments of thernPEO block of the surfactant with the silica-alumina framework. ~1H DipolarrnDephasing revealed that the amount of segments rigidified by this interactionrnincreased with the maturation time. The increased rigidity of the surfactant is tornbe linked with the increased mesoscopic ordering during maturation, resulting inrnthe higher mesoporous surface obtained after calcinations. The invariability ofrnthe TRAPDOR effect proved that the strength of the interaction, that is therndegree of interpenetration of the organic/inorganic phases remained the samernirrespective of maturation time. Together with the dramatic decrease of thernmicroporous volume with maturation time, this established that the origin of thernmicroporosity of AlSBA-15 is to be found in the incomplete hydrolysis of thernTEOS precursor itself rather than in the incomplete PEO– aluminosilicate phasernseparation.