SYNTHESIS AND STRUCTURE DETERMINATION OF ECR-10 - A GALLOSILICATE ZEOLITE WITH THE RHO-FRAMEWORK

Gallosilicate zeolites, termed ECR-10, have been crystallized from gel compositions aCs(2)O:bNa(2)O:Ga2O3:cSiO(2):dH(2)O gels with 0.5 < a < 0.8, 1.0 < b < 2.0, 2 < c < 2.5, and 50 < d < 100. ECR-10 has a typic al composition of Na2.7Cs2.1Si6.9Ga4.8O24. nH(2)O (Si:Ga = 1.4), a cub ic unit cell with a(o) similar to 14.9 Angstrom and the same framework topology as that of the aluminosilicate zeolite rho (RHO-framework), The Si:Ga ratios typical of ECR-10 are substantially smaller than the Si:Al ratios of zeolite rho materials; attempts to synthesize either E CR-10 or rho in overlapping composition domains have not, to date, bee n successful. Distance least-squares modeling was used to demonstrate the feasibility of accommodating the required number of framework gall ium atoms in the unit cell observed for ECR-10. Subsequent refinement of this trial structure for the dehydrated zeolite was achieved by Rie tveld analysis of monochromatic powder neutron diffraction data. The d erived structural parameters are compared with those of other RHO-fram ework materials. Framework gallium substitution leads to a substantial distortion of the eight-ring windows, reducing the effective pore dim ensions and suggesting the possibility of pore dimension control via p artial framework cation substitution.