Retrosynthetic Co-Templating Method for the Preparation of Silicoaluminophosphate Molecular Sieves

A retrosynthetic
method has been developed to design the synthesis
of target zeotypes whose frameworks belong to the ABC-6 structural
family and which contain gme cages. This permits
the preparation of silicoaluminophosphate versions of AFX (SAPO-56),
SFW (STA-18), and GME (STA-19) topology types. The method makes simultaneous
use of two organic structure-directing agents (SDAs) to promote the
formation of structural features such as cages or channels of the
target framework. Computational modeling was used to identify SDAs
for gme and other cages or channels in the target
structures. The trimethylammonium cation was found to be the most
favorable SDA for the gme cage while bisdiazabicyclooctane
(DABCO) alkane cations and quaternary ammonium oligomers of DABCO
with connecting polymethylene chain lengths of 4–8 methylene
units acted as templates for the additional cages or channels, respectively.
The incorporation of each of the co-SDAs in the as-prepared materials
was confirmed by chemical analysis, 13C MAS NMR, and Rietveld
refinement combined with computational modeling. Calcination of the
SAPO-56, STA-18, and some of the STA-19 materials gives microporous,
fully tetrahedrally coordinated framework solids with AFX, SFW, and
GME topologies: other STA-19 samples convert topotactically to SAPO-5.
These results show that SAPOs in the ABC-6 family can be prepared
via a targeted co-templating approach.