Synthesis and characterization of high-silica zeolite RHO prepared in the presence of 18-crown-6 ether as organic template

Pure high-silica RHO-type zeolite samples with a framework SiAl molar ratio as high as 4.5 were prepared by using 18-crown-6 ether as an organic template from a starting aluminosilicate gel containing cesium cations. The solids were characterized by elemental analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) thermal analysis, solid-state nuclear magnetic resonance (NMR) spectroscopy and n-hexane adsorption. The NH3 stepwise thermal desorption (STD) curve of high-silica zeolite rho shows stronger acid sites than for a FAU-type material with similar SiAl molar ratio. High-temperature XRD analyses performed on the protonated hydrated form of high-silica zeolite rho showed no framework flexibility, presumably because of a higher covalent character of the framework.