Preparation of MCM-48 materials with enhanced hydrothermal stability

A supercritical fluid method has been developed to prepare hydrothermally stable, high quality mesoporous MCM-48 materials. Pure silica MCM-48 materials were post-treated by supercritical carbon dioxide containing a small amount of aluminum tri-sec-butoxide (sc-CO₂/Al). The hydrothermal stability of these treated MCM-48 materials in boiling water was studied by powder X-ray diffraction, nitrogen absorption analysis, transmission electron microscopy, and ²⁹Si and ²⁷Al MAS NMR. ²⁷Al MAS NMR studies suggest that incorporation of the tetrahedral Al atoms into the framework of MCM-48 plays an essential role in enhancing the hydrothermal stability of these materials. For comparison, precursors containing other atoms, including Zr and Ti were also tested but most of these were found to have little influence on the hydrothermal stability of MCM-48.