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.