EMM-23: A Stable High-Silica Multidimensional Zeolite with Extra-Large Trilobe-Shaped Channels

Stable,
multidimensional, and extra-large pore zeolites are desirable
by industry for catalysis and separation of bulky molecules. Here
we report EMM-23, the first stable, three-dimensional extra-large
pore aluminosilicate zeolite. The structure of EMM-23 was determined
from submicron-sized crystals by combining electron crystallography,
solid-state nuclear magnetic resonance (NMR), and powder X-ray diffraction.
The framework contains highly unusual trilobe-shaped pores that are
bound by 21–24 tetrahedral atoms. These extra-large pores are
intersected perpendicularly by a two-dimensional 10-ring channel system.
Unlike most ideal zeolite frameworks that have tetrahedral sites with
four next-nearest tetrahedral neighbors (Q4 species), this
unusual zeolite possesses a high density of Q2 and Q3 silicon species. It is the first zeolite prepared directly
with Q2 species that are intrinsic to the framework. EMM-23
is stable after calcination at 540 °C. The formation of this
highly interrupted structure is facilitated by the high density of
extra framework positive charge introduced by the dicationic structure
directing agent.

在催化与大型分子分离领域，工业界对稳定、多维度及超大型孔道的沸石材料有着极高的需求。本研究报道了一种名为EMM-23的全新稳定三维超大型孔道铝硅酸盐沸石，该沸石的晶体结构是通过结合电子晶体学、固态核磁共振波谱（NMR）以及粉末X射线衍射技术从亚微米级晶体中确定的。其骨架内含有高度罕见的三角形孔道，这些孔道由21至24个四面体原子所围成。这些超大型孔道被一个二维的十元环通道系统垂直交叉。与大多数理想沸石框架中四面体位点仅具有四个最近邻四面体相邻原子（Q4物种）的情况不同，这种独特的沸石拥有高密度的Q2和Q3硅物种。这是首次通过直接利用框架内固有的Q2物种制备的沸石。EMM-23在540°C的煅烧后依然保持稳定。这种高度中断结构的形成得益于由阳离子结构导向剂引入的高密度额外框架正电荷。