Treatment of calcined MSU-S with NaAlO2 solution in the presence of CTAB: Change of acidic and catalytic properties

A hydrothermal post-synthesis modification method is introduced as a convenient but efficient route to improve aluminum content and acid amount of hexagonal MSU-S by treatment of it with NaAlO2 solution in the presence of cationic cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions. The speciality of this post-synthesis method, as compared with those reported studies on post-synthesis of Al-containing mesoporous materials, was that it took advantage of the hydrothermally unstable character of silica/aluminosilicate based mesoporous materials which would be partially dissolved in this highly-basic system and the templating function of CTAB. Indeed, characterization results based on a series of techniques (XRD, SEM, TEM, ICP elemental analysis, DSC, 27Al-NMR, FTIR and NH3-TPD) clearly proved that CTAB added in this modification process played a crucial role in the introduction of Al into the final solids via self-assembly with additionally introduced AlO2- and partly dissolved silicates from the parent MSU-S particles. In this way, Al amount determined by ICP and 27Al-NMR, acid content measured by NH3-TPD and therefore catalytic performance of the resultant samples characterized by cumene cracking were substantially improved in comparison with the parent MSU-S. It was also found that, if no CTAB in the modification procedure, the initial well-ordered MSU-S would be severely destroyed losing its mesoporous feature.