Abstract:

The external surface of 2D (two-dimensional) ZSM-5 zeolite was passivated by fabricating full silica Silicalite-1 through secondary crystallization technique. The obtained catalysts were characterized by XRD, SEM, TEM, N₂ adsorption-desorption isotherms, and Py-IR, etc. The catalytic performances of the surface passivated two-dimensional ZSM-5 zeolite in the alkylation between toluene and methanol were evaluated in a fixed-bed reactor. The characterization results showed that the full silica Silicalite-1 passivated 2D ZSM-5 zeolites with internal 2D lamellar structure were successfully constructed, and the Silicalite-1 not only effectively shielded the Brønsted acid sites on the external surface of 2D ZSM-5 zeolite and inhibited the occurrence of xylene isomerization, but also possessed the ability of shape-selectivity towards PX (p-xylene), which greatly improved the selectivity of p-xylene. The surface passivated 2D ZSM-5 zeolite also showed a long lifetime at 673K, and WHSV=10h^-1, and maintained high activity after 40h, with the selectivity of p-xylene about 35%, indicating an excellent catalytic performance in the alkylation of toluene with methanol. The present research could accelerate the industrialization procedure of alkylation between toluene and methanol.

Key words: ZSM-5, nanostructure, p-xylene, zeolite, multiphase reaction

摘要：

采用二次晶化技术在二维ZSM-5分子筛表面构筑了具有外表面钝化作用的全硅Silicalite-1结构，通过XRD、SEM、TEM、N₂吸附-脱附等温线、Py-IR等手段对所制备的催化剂进行表征，采用固定床反应器评价了表面钝化型二维ZSM-5分子筛在甲苯和甲醇烷基化反应中的催化性能。表征结果表明：二次晶化技术在保留ZSM-5分子筛内部二维片层结构的同时成功构筑了全硅Silicalite-1钝化表面，Silicalite-1钝化结构不仅能有效屏蔽二维ZSM-5分子筛外表面Brønsted酸位点，抑制二甲苯异构化副反应的发生，而且对PX（对二甲苯）具有择形扩散的性能，极大提高对二甲苯选择性。实验结果显示：表面钝化型二维ZSM-5分子筛在673K、WHSV=10h^-1的条件下表现出了较长的寿命，同时在反应40h后依然有较高的活性，且对二甲苯选择性达到了约35%，在甲苯与甲醇烷基化反应中表现出优异的催化性能，有效促进了甲苯与甲苯烷基化高选择性地制备对二甲苯的工业化应用进程。

关键词: ZSM-5, 纳米结构, 对二甲苯, 分子筛, 多相反应