Dual-Route Accessible Zeolites: bridging organic- and inorganic-directed syntheses toward greener zeolite production

The drive toward sustainable chemistry demands zeolite synthesis strategies that bypass organic structure-directing agents (OSDAs), primarily to circumvent the economic and environmental burdens associated with their use and removal. In this review, we introduce the concept of Dual-Route Accessible Zeolites-zeolite frameworks of identical topology that can be synthesized via both OSDA-assisted and OSDA-free routes. This concept provides a unifying framework for understanding crystallization mechanisms and structure-property relationships. Known zeolites are systematically classified into three categories in terms of synthetic routes: exclusively inorganic, dual-route accessible, and OSDA-dependent. Representative case studies-including Beta, CHA, FAU, LTA, and MFI-are examined to elucidate the distinct roles of inorganic cations, seed engineering, and synthesis conditions in directing zeolite formation. By extracting generalizable principles from these dual-route accessible systems, this review provides strategic guidance for the rational design of OSDA-free synthesis routes. By addressing both economic and environmental considerations, this review connects fundamental insights into zeolite crystallization with practical applications in materials science, catalysis, and sustainable engineering. Together, these perspectives establish a conceptual foundation for green design of zeolite materials.