Aluminum incorporation and interfacial structures in AISBA-15 mesoporous solids: double resonance and optically pumped hyperpolarized 129 Xe NMR studies

Aluminum-incorporated SBA-15 mesoporous materials have been obtained by direct synthesis. The surfactant—aluminosilicate interaction during synthesis was studied by double resonance NMR and confronted with the structural properties of the materials obtained after calcinations. Continuous-flow laser-polarized 129 Xe NMR spectroscopy was applied for the first time to explore the porosity of the AlSBA-15 mesoporous molecular sieves. TRAPDOR experiments firmly established a strong interaction between segments of the PEO block of the surfactant with the silica-alumina framework. 1 H Dipolar Dephasing revealed that the amount of segments rigidified by this interaction increased with the maturation time. The increased rigidity of the surfactant is to be linked with the increased mesoscopic ordering during maturation, resulting in the higher mesoporous surface obtained after calcinations. The invariability of the TRAPDOR effect proved that the strength of the interaction, that is the degree of interpenetration of the organic/inorganic phases remained the same irrespective of maturation time. Togethe with the dramatic decrease of the microporous volume with maturation time, this established that the origin of the microporosity of AlSBA-15 is to be found in the incomplete hydrolysis of the TEOS precursor itself rather than in the incomplete PEO— aluminosilicate phase separation.