ZSM-5/SBA-15 microporous/mesoporous composites prepared by a microwave-assisted zeolitisation of Al-SBA-15 mesoporous solids
Résumé
ZSM-5/SBA-15 composites with high textural properties were synthesised by a microwave-assisted zeolitisation of Al-SBA-15 in the presence of tetrapropylammonium bromide. The effect of the hydrothermal treatment temperature and of ammonium fluoride, often used as a catalyst, was studied. Resulting materials were characterised by XRD, SEM, N2 sorption, HR-TEM, hyperpolarised Xe NMR, pyridine sorption as well as by their stability toward boiling water. It was shown that the hydrothermal synthesis has to be carried out at 140 °C in order to better preserve the structure of the mesoporous precursor. Composite materials could be obtained only from a fluoride-free synthesis at short crystallisation times, t < 5 h. Appearance of 2-5 nm nanoparticles in some of the corresponding samples, has been related to the increase in the total acidity. Inclusion of zeolitic material in the remaining Al-SBA-15 structure was demonstrated by hyperpolarised xenon NMR studies.