Topotactic Conversion of Alkali‐Treated Intergrown Germanosilicate CIT‐13 into Single‐Crystalline ECNU‐21 Zeolite as Shape‐Selective Catalyst for Ethylene Oxide Hydration.

The conversion of the alkali‐treated intergrowth germanosilicate CIT‐13 into the single‐crystalline high‐silica ECNU‐21 (named after East China Normal University) zeolite, with a novel topology and a highly crystalline zeolite framework, has been realized through a creative top‐down strategy involving a mild alkaline‐induced multistep process consisting of structural degradation and reconstruction. Instead of acid treatment, hydrolysis in aqueous ammonia solution not only readily cleaved the chemically weak Ge(Si)−O−Ge bonds located within the interlayer double four ring (D4R) units of CIT‐13, but also cleaved the metastable Si−O−Si bonds therein. This led to extensive removal of the D4R units, and also generated silanol groups on adjacent silica‐rich layers, which then condensed to form a novel daughter structure upon calcination. Individual oxygen bridges in the reassembled ECNU‐21 replaced the germanium‐rich D4R units in CIT‐13, thereby eliminating the original intergrowth phenomenon along the b axis. With an ordered crystalline structure of 10‐ring (R) channels as well as suitable germanium‐related Lewis acid sites, ECNU‐21 serves as a stable solid Lewis acid catalyst for the shape‐selective hydration of ethylene oxide (EO) to ethylene glycol (EG) at greatly reduced H2O/EO ratios and reaction temperature in comparison with the noncatalytic industrial process. Zeolite transformations: The structural conversion from polymorph germanosilicate CIT‐13 to the novel ECNU‐21 zeolite has been achieved for the first time by an alkali treatment strategy (see figure). With a moderate Lewis acidity, ECNU‐21 serves as a promising shape‐selective catalyst for the hydration of ethylene oxide, with a conversion of more than 97 % and selectivity towards ethylene glycol of around 96 %. [ABSTRACT FROM AUTHOR]