Direct Synthesis and Characterization of Titanium-Substituted Mesoporous Molecular Sieve SBA-15

Abstract

Ti-substituted mesoporous SBA-15 (Ti−SBA-15) materials have been synthesized by using a new approach in which the hydrolysis of the silicon precursor (tetramethoxysilane, TMOS) is accelerated by fluoride. These materials were characterized by powder X-ray diffraction patterns (XRD), X-ray fluorescence spectroscopy (XRF), N2 sorption isotherms, diffuse-reflectance UV−visible (UV−vis) and UV−Raman spectroscopy, 29Si MAS NMR, and the catalytic epoxidation reaction of styrene. Experiments show that Ti−SBA-15 samples of high quality can be obtained under the following conditions: F/Si ≥ 0.03 (molar ratio), pH ≤ 1.0, aging temperature ≤ 80 °C, and Ti/Si ≤ 0.01. It was found that the hydrolysis rate of TMOS was remarkably accelerated by fluoride, which was suggested to play the main role in the formation of Ti−SBA-15 materials of high quality. There is no stoichiometric incorporation of Ti, and the Ti contents that are obtained are quite low in the case of the approach that is proposed. The calcined Ti−SBA-15 materials show highly catalytic activity in the epoxidation of styrene.