T. Chatelain et al., SYNTHESIS AND CHARACTERIZATION OF HIGH-SILICA ZEOLITE-RHO PREPARED INTHE PRESENCE OF 18-CROWN-6 ETHER AS ORGANIC TEMPLATE, Microporous materials, 4(2-3), 1995, pp. 231-238
Pure high-silica RHO-type zeolite samples with a framework Si/Al molar
ratio as high as 4.5 were prepared by using 18-crown-6 ether as an or
ganic template from a starting aluminosilicate gel containing cesium c
ations. The solids were characterized by elemental analysis, scanning
electron microscopy (SEM), X-ray diffraction (XRD) thermal analysis, s
olid-state nuclear magnetic resonance (NMR) spectroscopy and n-hexane
adsorption. The NH3 stepwise thermal desorption (STD) curve of high-si
lica zeolite rho shows stronger acid sites than for a FAU-type materia
l with similar Si/Al molar ratio. High-temperature XRD analyses perfor
med on the protonated hydrated form of high-silica zeolite rho showed
no framework flexibility, presumably because of a higher covalent char
acter of the framework.