晶化温度及 pH 值调节对中孔 MCM-41 分子筛合成的影响

Effects of Crystallization Temperature and pH Adjustment on Mesoporous MCM 41 Molecular Sieve Synthesis

在ＳｉＯ２－Ｎａ２Ｏ－Ｃ１６ＴＭＡ－Ｈ２Ｏ的四元水热体系中，借助ＸＲＤ及Ｎ２吸附等温线等测试手段详细考察了晶化温度的变化对中孔ＭＣＭ－４１分子筛合成的影响。实验结果表明，随晶化温度的提高，产物ＸＲＤ主衍射峰向２θ角的低角方向移动，孔壁硅酸盐的聚合度增大，孔壁厚度增加，这在一定程度上将有利于产物热稳定性的提高。但由于用作模板剂的表面活性剂分子聚集体形成的胶团因晶化温度的提高而发生变形或部分破坏，进而使产物中孔孔道结构的有序度严重下降。然而，若在高温晶化期间适当调节反应体系的ｐＨ值，却能明显改善高温对产物中孔孔道结构有序度的破坏程度。说明高质量中孔ＭＣＭ－４１分子筛的合成不仅受晶化温度变化的影响，而且与晶化期间ｐＨ值的调节密切相关。

The effect of crystallization temperature change on mesoporous MCM 41 molecular sieve synthesis is studied systematically in the hydrothermal system of Na 2O SiO 2 C 16 TMA H 2O using a combination of XRD and N 2 adsorption measurements.The experimental results show that rising crystallization temperature will shift the major XRD peak of products to smaller 2 θ angle,and both the degree of polymerization of the silicate on the product pore wall and its thickness of the pore wall will increase markedly.This will be advantageous to the improvement of the thermal stability of products.Unfortunately,the crystallinity of the samples and the ordered level of mesoporous molecular sieve framework are rapidly deteriorated as the micellar formation is not favourable or has been disrupted during high temperature crystallization.However,this deterioration tendency of mesoporous framework structure caused by high temperature can be improved greatly by means of pH adjustment for reaction mixture during synthesis.These facts indicate that the synthesis of high quality mesoporous MCM 41 molecular sieve is related not only to the change of synthesis temperature,but also to the pH adjustment during crystallization.