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-hydroth ermal treatment in 0.1 N NaF solutions on phase transformation and hydrothe rmal stability of mesoporous material, M41S, have been investigated. Hydrot hermally stable MCM-48 was successfully synthesized at 150 degreesC for var ious reaction times through phase transformation depending on the amount of NaF added to reacting solution. The results show that NaF as well as surfa ctant 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 li mited region on ternary diagram such as SiO2 > 45, HTA (surfactant) > 30 an d NaF < 20 in percent mole. The results also clearly show that a hydrotherm al post-treatment in 0.1 N NaF solution as well as direct addition of NaF c ould 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 ad dition and hydrothermal post-treatment could maximize the hydrothermal stab ility of MCM-48. (C) 2001 Elsevier Science B.V. All rights reserved.