Synthesis of Zeolite ZSM-5 Small Particle Aggregates by a Two-Step Method in the Absence of an Organic Template

The preparation of zeolite ZSM-5 without using a template was extensively investigated. Zeolite ZSM-5 small particle aggregates were synthesized in the absence of a template using sodium silicate as the silica source and by controlling the nucleation time at high temperature with a simple two-step method in a rotating autoclave on a spit within an oven. The first stage at higher temperature consisted of accelerating the nucleation and the second stage at lower temperature consisted of obtaining small crystals in the absence of a template. The resulting zeolites were characterized by X-ray powder diffraction, scanning electron microscopy, ammonia temperature-programmed desorption, and N2 adsorption. Compared with the micron-sized zeolite crystals that are synthesized in the one-step method, zeolite ZSM-5 small particles prepared by the two-step method have a higher specific surface area and an equivalent acid site content. The sample synthesized by the two-step method mainly contains Brönsted acid sites and a few Lewis acid sites indicating that Al is incorporated into the framework of the zeolite.

摘要在无模板剂存在下, 以硅酸钠为硅源采用简单的变温两步法, 通过控制高温预晶化时间, 在转动烘箱中成功合成了小颗粒 ZSM-5 沸石团聚体. 高温预晶化是为了加快反应液的成核, 而低温晶化是为了获得小的分子筛晶体. 运用 X 射线衍射, 扫描电镜, NH3 程序升温脱附和 N2 吸附-脱附等技术对合成的 ZSM-5 沸石进行了表征. 与一步法合成的微米级颗粒相比较, 两步法合成的小颗粒团聚体 ZSM-5 沸石具有较高比表面积和相同酸量. 得到的沸石的 Brönsted 酸位占主要部分, Lewis 酸位较少, 也说明 Al 基本进入沸石骨架中.

Graphical abstractZeolite ZSM-5 small particle aggregates with a high specific surface area were synthesized without a template using a two-step method in a rotating autoclave on a spit within an oven.Figure optionsDownload full-size imageDownload as PowerPoint slide