Characterization and investigation mechanism of hydrothermal stability for micropore-free ordered mesoporous molecular sieves

SBA-15-type mesoporous aluminosilicates molecular sieves (MSAMS-2 and MSAMS-4) were synthesized and characterized by N2 adsorption–desorption, XRD, FT-IR, TG/DTA, FE-SEM, TEM and HR-TEM. N2 adsorption–desorption and t-plots of N2 adsorptions show the two sieves are free of micropores within their mesoporous framework wall. MSAMS-2 and MSAMS-4 exhibit extraordinary stability both in boiling water (over 360 h) and in high temperature steam (800 °C for 6 h). FT-IR together with XRD, TG/DTA, HR-TEM and FE-SEM characterizations demonstrate that five-membered ring subunits with small size rather than zeolite crystals were only formed within the framework pores of MSAMS-2 and MSAMS-4. These five-membered ring subunits are extraordinarily stable and can effectively keep them from water molecule attack, which should play a crucial role in improving the hydrothermal stability for MSAMS-2 and MSAMS-4.