posted on 1996-08-15, 00:00authored byTina M. Nenoff, John B. Parise, Glover A. Jones, Laurine G. Galya, David R. Corbin, Galen D. Stucky
This is an extensive study of the non-aluminosilicate analogs of
the zeolite RHO. This molecular sieve is of
great interest commercially because of its catalytic properties.
In the absence of rigid supporting structural
subunits (smaller cages or channels), the aluminosilicate RHO exhibits
atypical framework flexibility with
large displacive rearrangements. The beryllophosphate and
berylloarsenate analogs are easily synthesized
under very mild reaction conditions and therefore may be of interest
for inexpensive and rapid commercial
production. However, they have decreased thermal stability.
In an effort to increase thermal stability and
explore framework flexibility, we have synthesized and characterized a
series of analogs of the non-aluminosilicate RHO framework. All materials crystallize in the
space group I23, ranging from a =
13.584(2) Å for Li-BePO RHO to a = 14.224(4) Å for
Ba-RbBeAsO RHO for hydrated phases. The extra
framework
cations are distributed over the double 8-ring, single 8-ring, and two
single 6-ring sites. Partially and fully
dehydrated phases were also studied for changes in framework stability.
Predictive trends based on the type
of cation exchanged into the framework were determined by
9Be and 31P MAS NMR.