ICGM UMR 5253 CNRS-Univ Montpellier-ENSCM , ENSCM 240 Avenue Pr E. Jeanbrau , 34296 Montpellier Cedex 5, France.
Laboratoire de Chimie de la Matière Condensée, LCMCP, Collège de France , Sorbonne Université, CNRS , F-75005 Paris , France.
Langmuir. 2018 Sep 25;34(38):11414-11423. doi: 10.1021/acs.langmuir.8b03010. Epub 2018 Sep 14.
The texture of mesoporous FAU-Y (FAUmes) prepared by surfactant-templating in basic media is a subject of debate. It is proposed that mesoporous FAU-Y consists of: (1) ordered mesoporous zeolite networks formed by a surfactant-assisted zeolite rearrangement process involving local dissolution and reconstruction of the crystalline framework, and (2) ordered mesoporous amorphous phases as Al-MCM-41, which coexist with zeolite nanodomains obtained by a dissolution-reassembly process. By the present systematic study, performed with FAU-Y (Si/Al = 15) in the presence of octadecyltrimethylammonium bromide and 0 < NaOH/Si ratio < 0.25 at 115 °C for 20 h, we demonstrate that mesoporous FAU zeolites consist, in fact, of a complex family of materials with textural features strongly impacted by the experimental conditions. Two main families have been disclosed: (1) for 0.0625 < NaOH/Si < 0.10, FAUmes are ordered mesoporous materials with zeolite walls, which coexist with zeolite nanodomains (100-200 nm) and (2) for 0.125 < NaOH/Si < 0.25, FAUmes are ordered mesoporous materials with amorphous walls as Al-MCM-41, which coexist with zeolite nanodomains (5-100 nm). The zeolite nanodomains decrease in size with the increase of NaOH/Si ratio. Increasing NaOH/Si ratio leads to an increase of mesopore volume, while the total surface area remains constant, and to a decrease of strong acidity in line with the decrease of micropore volume. The ordered mesoporous materials with zeolite walls feature the highest acidity strength. The ordered mesoporous materials with amorphous walls present additional large pores (50-200 nm), which increase in size and amount with the increase of NaOH/Si ratio. This alkaline treatment of FAU-Y represents a way to obtain ordered mesoporous materials with zeolite walls with high mesopore volume for NaOH/Si = 0.10 and a new way to synthesize mesoporous Al-MCM-41 materials containing extralarge pores (50-200 nm) ideal for optimal diffusion (NaOH/Si = 0.25).
介孔 FAU-Y（FAUmes）的结构一直存在争议，其是通过表面活性剂模板在碱性介质中制备的。有人提出介孔 FAU-Y 由以下两部分组成：（1）由表面活性剂辅助沸石重排过程形成的有序介孔沸石网络，涉及晶体骨架的局部溶解和重建；（2）与通过溶解-重组过程获得的沸石纳米域共存的有序介孔无定形相，如 Al-MCM-41。通过本系统研究，使用 Si/Al 比为 15 的 FAU-Y，在 115°C 下，使用十六烷基三甲基溴化铵，0 < NaOH/Si 比 < 0.25，反应 20 小时，我们证明介孔 FAU 沸石实际上由具有强烈受实验条件影响的结构特征的复杂材料家族组成。已经揭示了两个主要家族：（1）对于 0.0625 < NaOH/Si < 0.10，FAUmes 是具有沸石壁的有序介孔材料，与沸石纳米域（100-200nm）共存；（2）对于 0.125 < NaOH/Si < 0.25，FAUmes 是具有无定形壁的有序介孔材料，如 Al-MCM-41，与沸石纳米域（5-100nm）共存。沸石纳米域的尺寸随 NaOH/Si 比的增加而减小。随着 NaOH/Si 比的增加，介孔体积增加，而总表面积保持不变，强酸性随着微孔体积的减小而减小。具有沸石壁的有序介孔材料具有最高的酸强度。具有无定形壁的有序介孔材料具有额外的大孔（50-200nm），其随 NaOH/Si 比的增加而增大。FAU-Y 的这种碱性处理是获得具有高介孔体积的沸石壁有序介孔材料的一种方法（NaOH/Si = 0.10），也是合成含有理想扩散的大孔（50-200nm）的介孔 Al-MCM-41 材料的新方法（NaOH/Si = 0.25）。
