Molecularly engineered zeolites with extra-large-pore architectures and functional opportunities

Abstract

Zeolites are crystalline microporous materials extensively applied in ion exchange, adsorption, separation, and catalysis. However, small-, medium-, and large-pore zeolites with 8–12-membered-ring (MR) frameworks suffer from intrinsic diffusion and reactivity limitations in the conversion of bulky molecules. Recent advances in molecular engineering have enabled the synthesis of extra-large-pore (ELP) frameworks with window sizes exceeding 12-MRs, which bridge the gap between microporous and mesoporous materials. These architecturally unique ELP zeolites facilitate the diffusion of bulky molecules, unlocking opportunities in catalysis, separation, and environmental remediation. This review consolidates the rapidly expanding field of ELP zeolites, providing a comprehensive overview ranging from early germanosilicate and phosphate-based systems to recent high-silica and aluminosilicate ELP frameworks with three-dimensional interconnected pore networks. First, we delineate the structural characteristics of ELP zeolites (ring aperture, framework density, and pore dimensionality) and discuss advanced characterisation techniques that have enabled their precise structural elucidation. We then systematically summarise the synthetic methodologies, encompassing the prevailing ‘bottom-up’ and ‘top-down’ strategies, as well as emerging approaches such as high-throughput screening and machine learning-guided framework design. Representative ELP zeolites across phosphate-, germanosilicate-, pure-silica, aluminosilicate-, and heteroatom-containing frameworks are examined with respect to their functional potential in adsorption, separation, and catalysis. Finally, key challenges, including the high cost of multi-step templating, reliance on germanium, structural framework defects, and environmentally unsustainable synthesis methods, are highlighted, along with perspectives on accelerating the development of next-generation ELP zeolites through data-driven design integrated with in situ characterisation.