具有强酸性位的高水热稳定介孔分子筛的合成

Hydrothermally Stable Mesoporous Aluminosilicates with Strongly Acidic Sites

在强酸性介质中,以预先制备的β沸石纳米簇作为前驱体,通过S+X-I+路线及氨水热后处理步骤合成具有强酸性位的高水热稳定性介孔分子筛.XRD、氮气吸附、HRTEM和SEM分析表明所得样品具有普通MCM-41的典型介孔结构和表观形貌.较短的组装周期和室温的组装条件减弱了脱铝效应,27AlMASNMR表明铝元素主要以四配位状态存在于介孔分子筛骨架中.采用NH3-TPD和水热老化方法分别考察了其固体酸性和水热稳定性,结果表明此介孔分子筛相对于普通MCM-41分子筛具有较强酸性位和较高的水热稳定性.沸石纳米簇的引入提高了分子筛骨架的聚合度和孔壁的厚度,是水热稳定性提高的主要原因.

Mesoporous aluminosilicates were synthesized through S+X-I+ route using preformed beta zeolitic nanoclusters as building units in acidic media and subsequent ammonia hydrothermal treatment. The ordered mesoporous aluminosilicates were characterized by XRD, N-2 adsorption and desorption, HRTEM, SEM, NMR and NH3-TPD methods. The results indicated that the sample had the same hexagonal mesostructures as normal MCM-41 synthesized in acidic media. The presence of strongly acidic sites was substantiated by NH3-TPD study, and the hexagonal mesoporous structure was maintained even after 120 h treatment in boiling water. The synthesized materials were superior to conventional MCM-41 with respect to their stronger acidity and higher hydrothermal stability. The short period of assembly in acidic media and the ambient temperature reduced the dealumination effect considerably. The retention of zeolite-like connectivity of tetrahedral AlO4 and SiO4 units upon assembling the nanoclusters into mesostructured materials and the thicker framework pore walls contributed to the especially good hydrothermal stability greatly, which also gave rise to the presence of strong acidity.