Synthesis of MCM-48 via phase transformation with direct addition of NaF and enhancement of hydrothermal stability by post-treatment in NaF solution

The effects of direct addition of NaF to reacting solution and post-hydrothermal treatment in 0.1 N NaF solutions on phase transformation and hydrothermal stability of mesoporous material, M41S, have been investigated. Hydrothermally stable MCM-48 was successfully synthesized at 150 degreesC for various reaction times through phase transformation depending on the amount of NaF added to reacting solution. The results show that NaF as well as surfactant to silica ratio plays an important role for the formation of pure MCM-48. It was observed that pure MCM-48 appears to be formed easily but in limited region on ternary diagram such as SiO2 > 45, HTA (surfactant) > 30 and NaF < 20 in percent mole. The results also clearly show that a hydrothermal post-treatment in 0.1 N NaF solution as well as direct addition of NaF could further enhance the hydrothermal stability of MCM-48. XRD, Si-29-MAS n.m.r. spectra, BET and TEM clearly support that a combined effect of NaF addition and hydrothermal post-treatment could maximize the hydrothermal stability of MCM-48. (C) 2001 Elsevier Science B.V. All rights reserved.