The synthesis of PST-2, an aluminosilicate zeolite intergrowth
of cage-based, large-pore SBS and SBT topologies, and its intergrowth
characteristics are presented. With the Si/Al ratio and crystallization
inorganic structure-directing agent in zeolite synthesis mixtures
fixed to 8.0 and Cs+ ions, respectively, pure PST-2 is
obtained at 120 °C using tetraalkylammonium ions with C/N+ ratios of 5–9 as a charge density mismatch (CDM) organic
structure-directing agent (OSDA). More interestingly, the intergrowth
ratio between SBS and SBT in PST-2 was found to vary notably not only
with the type of CDM OSDA employed but also with the crystallization
time, unlike the case of other well-known zeolite intergrowths such
as β and MFI/MEL. When tetraethylammonium ions are used as a
CDM OSDA at 100 °C in the presence of Cs+, the SBS
portion in PST-2 decreases from over 60% to less than 45% with increasing
crystallization time from 2.5 to 14 days, suggesting that SBS formation
is kinetically more favorable than SBT formation. A thorough characterization
of changes in the crystallite dimension of PST-2 with crystallization
time, together with those in the chemical composition, allowed us
to propose a plausible crystal growth mechanism of this large-pore
zeolite intergrowth