Improving the Hydrothermal Stability of Mesoporous Silica SBA-15 by Pre-treatment with (NH4)(2)SiF6

The hydrothermal stability of the mesoporous silica material SBA-15 was improved by a pre-treatment of 5 mol% ammonium hexafluorosilicate solution with 1 mol% SiO2 ratio of (NH4)(2)SiF6 and SBA-15. The modified SBA-15 kept its ordered meso-structure well even when kept under boiling water for 14 d or 100% H2O stream at 800 degrees C for 12 h, and still had BET surface areas as high as 310 and 213 m(2)/g, respectively, after these treatments. The possible reasons for the stabilization were that the surface defects of SBA-15 were partially repaired by silicon insertion and some silicon hydroxyls were replaced by F- ions. Larger amounts of ammonium hexafluorosilicate did not give more stabilization.