Sandwich-Type Zeolite Intergrowths with MFI and the Novel Extra-Large Pore IDM‑1 as Ordered End-Members

Stacking faults are
two-dimensional planar defects frequently arising
in zeolites, modifying their properties and potentially affecting
their performance in catalysis and separation applications. In classical
zeolite intergrowths, a topologically unique zeolite layer may often
pile up after some spatial transformation (lateral translation, rotation,
and/or reflection) that may occur in different amounts or directions
with about similar probabilities, leading to a difficult to control
disorder. Here, we present a new kind of zeolite intergrowth that
requires an additional topologically distinct layer rather than a
spatial transformation of a unique one. Stacking of the so-called
pentasil layers produces the well-known medium pore zeolite MFI. Intercalation
in strict alternation of a topologically distinct second layer sandwiched
between pentasil layers expands the structure to produce the new extra-large
pore IDM-1. Stacking disorder modulates the structural expansion along
the stacking direction. The disordered materials have been studied
by simulation of the X-ray diffraction patterns using the program
DIFFaX and by Cs-corrected high-resolution electron microscopy. We
show that disorder does not occur at random but in extended domains
and can be controlled all the way from MFI to IDM-1 by just varying
the concentration of the synthesis mixture.