Improving the stability of mesoporous MCM-41 silica via thicker more highly condensed pore walls
Improving the stability of mesoporous MCM-41 silica via thicker more highly condensed pore walls
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DOI：
10.1021/jp992233m
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发表时间：
1999-11-18
影响因子：
3.3
通讯作者：
Mokaya, R
中科院分区：
文献类型：
--
作者：
Mokaya, R
通过二次结晶（以煅烧的MCM-41为硅源）或延长结晶时间，制备了具有较好热稳定性和水热稳定性的厚壁介孔MCM-41硅。不同寻常的是，这些Si-MCM-41材料的合成（含有表面活性剂）形式的较厚孔壁主要由完全凝聚的二氧化硅单元组成。Q(4)/Q(3)比值高达3.4或4.5的两步（每48小时）结晶或96小时结晶在150℃下分别获得。提出了一种扩散控制机制，其中硅酸盐单元和表面活性剂分子不断添加到“种子”晶体上（在二次再结晶过程中）或添加到生长中的表面活性剂/硅酸盐聚集体上（在长结晶时间内），以解释孔壁增厚和更高的二氧化硅冷凝。
Thicker-walled mesoporous MCM-41 silicas with improved thermal and hydrothermal stability were prepared via secondary crystallization (in which calcined MCM-41 was used as silica source) or by using long crystallization times. Unusually, the thicker pore walls of the as-synthesized (surfactant containing) forms of these Si-MCM-41 materials are primarily made up of fully condensed silica units. Q(4)/Q(3) ratios as high as 3.4 or 4.5 are obtained for two-step (48 h each) crystallization or 96 h crystallization at 150 degrees C, respectively. A diffusion-controlled mechanism in which silicate units and surfactant molecules are continually added onto the "seed" crystals (during secondary recrystallization) or to the growing surfactant/silicate aggregate (for long crystallization time) is proposed to explain the pore wall thickening and higher silica condensation.