一步法合成多级孔结构ZSM-5分子筛

多级孔结构ZSM-5分子筛的合成过程复杂。利用双模板剂,通过优化晶化条件(如晶化时间与晶化温度)和Si/Al物质的量比等一步水热晶化合成了具有多级孔结构的ZSM-5分子筛,并采用XRD、N₂吸附-脱附、吡啶红外吸脱附、SEM和TEM等方法对样品的晶体结构、孔道结构、表面酸性和形貌等进行了表征。结果表明,一步法合成多级孔结构ZSM-5分子筛的适宜条件是:晶化温度160-180℃,晶化时间24-96 h,反应物组成为SiO₂/Al₂O₃/Na₂O/CTAB/TPABr/H₂O=1/x/0.4/0.05/0.12/280,(x:50-240)。其中,晶化温度160℃、晶化时间48 h和以Si/Al物质的量比50的凝胶合成的样品具有有序的介孔(平均尺寸3.60 nm)结构、较高的结晶度和较强的酸性。

One-step synthesis of hierarchical-structured ZSM-5 zeolite

Generally, the process for synthesis of hierarchical-structured ZSM-5 zeolite is complex. Here, the polygonal three-dimensional ZSM-5 zeolite with hierarchical structure was hydrothermally synthesized by one-step synthesis method with dual templates. The effects of crystallization conditions and synthesis gel compositions, including crystallization temperature, crystallization time, Si/Al molar ratio, on the products were investigated for optimizing synthesis conditions. The X-ray diffraction (XRD), N₂ adsorption-desorption experiment, Pyridine adsorption FT-IR (Py-FTIR), scanning electron microscopy (SEM) and transmission electron microscope (TEM) were used to characterize the crystalline structure, pore structure, surface acidity and crystal morphology of products. It was shown that the hierarchical-structured ZSM-5 zeolite can be synthesized under the following conditions: crystallization temperature of 160-180℃, crystallization time of 24-96 h, the SiO₂/Al₂O₃/Na₂O/CTAB/TPABr/H₂O ratio of 1/x/0.4/0.05/0.12/280, (x: 50-240). The sample crystallized at 160℃ for 48 h with a synthesis gel having a Si/Al molar ratio of 50 had uniform cylindrical crystal morphology, high crystallinity and ordered mesoporous structure with a pore diameter of 3.60 nm. It contains both strong Brønsted and Lewis acid sites at 300℃, which contribute to its catalytic properties.