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

Abstract

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% SiO 2 ratio of (NH 4 ) 2 SiF 6 and SBA-15. The modified SBA-15 kept its ordered meso-structure well even when kept under boiling water for 14 d or 100 % H 2 O stream at 800 °C for 12 h, and still had BET surface areas as high as 310 and 213 m 2 /g, respectively, after these treatments. Two possible reasons for the stabilization were: (i) surface defects of SBA-15 were partially repaired by silicon insertion and (ii) some silicon hydroxyls were replaced by F − ions. Larger amounts of ammonium hexafluorosilicate did not give more stabilization. (NH 4 ) 2 SiF 6 预处理可对 SBA-15 介孔材料的表面缺陷进行补硅修正以及表面疏水化, 从而明显改善 SBA-15 材料的水热稳定性. 结果表明, 用摩尔分数为 5% 的 (NH 4 ) 2 SiF 6 水溶液, 按引入 1% 的 SiO 2 计量对 SBA-15 进行处理后, 其水热稳定性明显改善, 在 100 r{ }C 沸水中处理 14 d, 或在 800 r{ }C 下用 100% 水蒸气处理 12 h 后, 均保持较好的介观有序度、形貌及六方孔道结构, 比表面积分别高达 310 和 213 m 2 /g, 但 (NH 4 ) 2 SiF 6 处理量过高, SBA-15 水热稳定性反而下降. Mesoporous silica SBA-15 modified by (NH 4 ) 2 SiF 6 exhibited improved hydrothermal stability, and could maintain its structure under boiling water for 14 days or 100% H 2 O stream at 800 °C for 12 hours.