Recent Synthesis Routes to Previously Inaccessible Zeolite Porosity: From Ultrasmall Pore to Ultraporous Materials

The diverse porosity and properties of zeolites, together with their stability, drive applications from catalysis to adsorption. Conventional hydrothermal synthesis has yielded a large number of zeolite framework types, the vast majority of which are synthetic. However, this approach still has limitations, as exemplified by the large disparity between known and hypothetical but feasible framework types. This Perspective highlights recent unconventional synthesis routes that expand the range of attainable structures and porosities: ultrasmall open pores by zeolite reconstruction; unfeasible zeolites with tunable pores by assembly disassembly organization-reassembly; the embedded isoreticular RHO zeolite family synthesized using mixed inorganic cations; shape selective small and medium pore zeolites synthesized via an excess fluoride approach; and phosphonium-enabled ultraporous zeolites (<13.2 tetrahedral atoms/1000 ų). Their associated applications include selective dehydration, CO₂ capture, catalysis, and decontamination. Although challenges such as scalability, organic structure-directing agent cost and emissions persist, these unconventional chemistries offer important opportunities for further evolution of zeolite structures for environmental, energy and health-related applications.