SYNTHESIS AND CHARACTERIZATION OF HIGH-SILICA ZEOLITE-RHO PREPARED INTHE PRESENCE OF 18-CROWN-6 ETHER AS ORGANIC TEMPLATE

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.