微米级MEL分子筛聚集体的制备

使用四丁基氢氧化铵-正硅酸四乙酯-水（TBAOH-TEOS-H₂O）简单体系一步水热制备了具有多级孔道的微米级MEL结构分子筛聚集体. 得到的silicalite-2 微米球直径大于10 μm且具有高达460 m²·g^-1的比表面积和0.74 cm³·g^-1的孔体积. 微米球的生成一定程度上解决了催化应用过程中催化剂的分离和回收问题. 同时，水热晶化过程中由纳米粒子自组装而成的晶间介孔缩短了反应物分子的扩散路径，保持了分子筛纳米晶粒的优势. 此外，钛活性位的引入并未明显影响MEL微米球的形貌和结构，含钛的MEL微米球TS（钛硅分子筛）-2在苯酚羟基化反应中具有与纳米尺寸TS-1（100-200 nm）相当的催化活性，且TS-2 可以通过简单过滤得到，简化了纳米级TS-1的分离和回收过程.

Synthesis of Micro-Sized MEL-Type Zeolite Aggregates

Hierarchical micro-sized zeolite aggregates with the MEL structure were prepared hydrothermally froma tetrabutylammoniumhydroxide (TBAOH)-tetraethyl orthosilicate (TEOS)-H₂O system. The obtained microsized silicalite-2 microspheres had sizes larger than 10 μm, high BET surface area (460 m²·g^-1), and large pore volume (0.74 cm³·g^-1). The formation of micro-sized spheres alleviates preparation and application difficulties. The presence of inter-crystalline mesopores originating from the spontaneous assembly of nano-sized primary particles during hydrothermal synthesis gives the advantages of nanoparticles, reducing diffusion limitations. The introduction of titanium does not strongly affect the morphology and textural properties of the MEL-type zeolite, which are quite similar to those of silicalite-2 aggregates. The micro-sized titanium silicalite-2 (TS-2) microspheres showed comparable catalytic activity in phenol hydroxylation to that of titanium silicalite-1 (TS-1) of size 100-200 nm, and were easily recovered by traditional filtration, simplifying the separation and recovery compared with nano-sized TS-1.