DOUBLE RESONANCE NMR STUDY OF MESOSCOPIC INTERACTION BETWEEN SURFACTANT AND SILICA-ALUMINA DURING THE DIRECT SYNTHESIS OF A1SBA-15 MESOPOROUS SOLIDS

摘要

The occurrence of a dipolar interaction of constant strength between the CH and CH_2 protons of the surfactant and the ~(27)A1 of the aluminosilicate in the composite parent material irrespective of the microporous volume of the final A1SBA-15 solid precluded the possibility that the microporosity of SBA-15 originates from the occlusion of part of the template in the oxide. The increased rigidity of the PPO-PEO-PPO backbone evidenced by the increasing fraction of protons in strong homonuclear interaction must be attributed to the forming mesoporous surface and thus to a larger amount of PPO fragments interacting with it. Actually, the microporous volume decreased drastically with maturation time as hydrolysis proceeded therefore suggesting that it resulted instead from incomplete condensation due to the TEOS not being fully hydrolyzed. In other words, the appearance of the microporous "corona" is not related to the surfactant behavior but is only due to the hydrolysis kinetics of TEOS under acidic conditions.