Breaking Structural Energy Constraints: Hydrothermal Crystallization of High-Silica Germanosilicates by a Building-Unit Self-Growth Approach.

Zeolites, a class of crystalline microporous materials, have a wide range of practical applications, in particular serving as key catalysts in petrochemical and fine-chemical processes. Millions of zeolite topologies are theoretically possible. However, to date, only 235 frameworks with various tetrahedral element compositions have been discovered in nature or artificially synthesized, among which approximately 50 topologies are available in pure-silica forms. Germanosilicates are becoming an important zeolite family, with a rapidly increasing number of topological structures having unusual double four-membered ring (D4R) building units and large-pore or extra-large-pore systems. The synthesis of their high-silica analogues with higher (hydro)thermal stability remains a great challenge, because the formation of siliceous D4R units is kinetically and thermodynamically unfavorable in hydrothermal systems. Herein, it is demonstrated that such D4R-containing high-silica zeolites with unexpected crystalline topologies (ECNU-24-RC and IM-20-RC) are readily constructed by a versatile route. This strategy provides new opportunities for the synthesis of high-silica zeolite catalysts that are hardly obtainable by conventional hydrothermal synthesis and may also facilitate a breakthrough in increasing the number and types of zeolite materials with practical applications.