Zeolite catalysts often face a fundamental trade-off between molecular accessibility and shape-selective confinement. Here, we show that this trade-off can be mitigated by accessing kinetically stabilized crystalline FAU–CHA intermediates during partial interzeolite transformation. Pair distribution function analysis reveals the coexistence of FAU- and CHA-derived structural motifs within the materials, consistent with the partial structural reorganization of the FAU framework during interzeolite transformation. In situ FT-IR spectroscopy demonstrates that these intermediates retain the Brønsted acid sites characteristic of both frameworks, whereas transient extra-framework aluminum species emerge and are progressively reincorporated into the zeolite lattice. Quantitative acidity measurements using ammonia and pyridine further show that the intermediates preserve a high density of Brønsted acid sites with markedly enhanced accessibility compared to the fully transformed CHA. Together, these results establish kinetically controlled interzeolite transformation as a route to crystalline zeolitic materials, in which accessibility and confinement are jointly encoded through intimate phase contact, with direct implications for catalytic reactions involving bulky substrates.

Determining the distribution of aluminium in zeolite frameworks remains a significant challenge, due to the limited sensitivity of conventional characterization techniques. To overcome this issue, we have developed a procedure which combines experimental two-dimensional (2D) solid-state NMR spectroscopy with machine learning (ML) techniques. To validate the approach, we have applied it to achieve a detailed assignment of Al environments in zeolite RTH. A reactive ML potential was used to model long-timescale framework dynamics under realistic conditions, including temperature and hydration, alongside the accurate prediction of isotropic NMR chemical shifts. Comparison between theoretical and experimental spectra reveals that Al preferentially occupies the T2 sites, with under-population of the other T-sites. The excellent agreement between computed and observed NMR data demonstrates that this ML-augmented spectroscopic approach is a powerful tool for quantitative elucidation of Al distributions in structurally complex zeolites, going far beyond the limitations of traditional quantum chemical approaches.

Interzeolite Transformation Intermediates (ITIs) produced by the partial interconversion of FAU to BEA zeolites were systematically investigated as catalysts for the cracking of low-density polyethylene (LDPE) and polystyrene (PS). These materials exhibit a unique combination of structural features, including strong Brønsted acidity and well-developed intracrystalline mesoporosity. Comprehensive characterization by XRD, N₂ physisorption, UV-Vis Raman spectroscopy, ²⁷Al MAS NMR, and TEM confirmed their hybrid nature, incorporating elements of both the parent FAU and daughter BEA zeolites. Catalytic performance was benchmarked against fully formed zeolites (FAU, BEA) and a mesoporous aluminosilicate (Al-MCM-41). For LDPE cracking, strong acidity and well-defined microporosity were found to be critical, with conventional zeolites outperforming ITIs. In contrast, ITIs exhibited superior catalytic activity and stability for PS cracking owing to their well-connected mesoporosity and balanced acidity profiles. A key finding of this study is that a catalyst with both large mesoporosity and the strongest acidity is not always the best. For example, PS cracking benefited from catalysts with moderate acidity and high mesoporosity, while LDPE cracking required materials with stronger acid sites. In all cases, ITIs outperformed mesoporous catalysts derived from amorphous precursors, with Al-MCM-41 consistently showing the lowest catalytic activity. Operando FT-IR-GC-MS provided insights into the reaction mechanisms and product distributions, revealing the role of ITIs in enhancing resistance to coking deactivation. ITIs were advantageous for PS dealkylation and for promoting the selective formation of olefins during LDPE cracking. Temperature-programmed oxidation (TPO) studies showed that the well-interconnected mesoporosity of ITIs facilitated coke oxidation compared to the poorly interconnected channels of conventional zeolites. These results highlight the potential of ITIs as tailor-made catalysts for plastic waste valorization, with performance tunable by their intermediate structural properties.