FLEXIBILITY OF THE ZEOLITE-RHO FRAMEWORK - IN-SITU X-RAY AND NEUTRON POWDER STRUCTURAL CHARACTERIZATION OF CATION-EXCHANGED BEPO AND BEASO-RHO ANALOGS

This is an extensive study of the non-aluminosilicate analogs of the z eolite RHO. This molecular sieve is of great interest commercially bec ause of its catalytic properties. In the absence of rigid supporting s tructural subunits (smaller cages or channels), the aluminosilicate RH O exhibits atypical framework flexibility with large displacive rearra ngements, The beryllophosphate and berylloarsenate analogs are easily synthesized under very mild reaction conditions and therefore may be o f interest far inexpensive and rapid commercial production. However, t hey 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 frame work. All materials crystallize in the space group 123, ranging from a = 13.584(2) Angstrom for Li-BePO RHO to a = 14.224(4) Angstrom for Ba -RbBeAsO RHO for hydrated phases. The extra framework cations are dist ributed over the double 8-ring, single 8-ring, and two single 6-ring s ites. Partially and fully dehydrated phases were also studied for chan ges in framework stability. Predictive trends based on the type of cat ion exchanged into the framework were determined by Be-9 and P-31 MAS NMR.