Formation of integrated MCM-41 mesostructure in fluoride medium: An improvement of hydrothermal stability

Abstract

The formation of regular hexagonal MCM-41 framework was systematically studied with cetyltrimethyl ammonium bromide as surfactant and aerosil-200 powder silica as silica source under static conditions in the presence of fluoride anions. The influence of various parameters like F-/Si ratio, Na+/Si ratio, CTMABr/Si ratio, temperature and Al/Si ratio, has been investigated. The optimal crystallization conditions are found to be within the range of F-/Si: 0.28-0.34, Na+/Si: 0.50-1.0, CTMABr/Si: about 0.50, and Si/Al>40 at 100-135°C with a fixed H2O/Si ratio of 100. The results show that the hydrothermal stability of MCM-41 synthesized in the presence of fluoride anions has been largely improved as compared to that prepared in the presence of chloride anions. The improvement of hydrothermal stability is suggested to be attributed to the formation of surface Si-F bonds having natural resistance to the hydrolysis with water molecules. © 2000 Elsevier Science B.V. All rights reserved.