Targeted Synthesis of Ultrastable High-Silica RHO Zeolite Through Alkali Metal-Crown Ether Interaction.

High-silica RHO zeolite was directly synthesized using an alkali metal-crown ether (AMCE) complex as organic structure-directing agent (OSDA). Derived from the UV-vis spectra and zeolite patterns, the crown ether-cesium cation interaction was found to have crucial effect on the enhancement of silica content within the zeolite framework. The synthesized RHO zeolites possess up to four times larger silica/alumina ratio (SAR) values than that in their conventional form, which gives them extraordinarily rigid frameworks even after hydrothermal aging under 800 °C. Compared to commercial zeolites, copper-exchanged high-silica RHO zeolites demonstrate considerably high reaction activity in NO removal, making them promising candidates for diesel exhaust treatment.