Authors: Joaquin Martínez-Ortigosa | Karolina A. Tarach | Oliwia Rogala | Noemi Linares | Kinga Góra‐Marek | Javier García‐Martínez
Source: Applied Catalysis B: Environmental (article, 2025-07-15)
Field: Chemistry — Inorganic Chemistry

Leveraging mesoporosity and acidity in interzeolite transformation intermediates for plastic waste valorization 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, it is 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. The lower catalyst tortuosity in ITIs was advantageous for PS dealkylation, promoting the selective formation of lighter more valuable hydrocarbons products. 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. • Interzeolite Transformation Intermediates (ITIs), created by partially converting FAU to BEA zeolites, offer a hybrid structure combining strong Brønsted acidity and well-connected mesoporosity, making them promising catalysts for plastic waste valorization. • For PS (an aromatic polymer), moderate acidity and high mesoporosity of ITIs yield superior catalytic activity and stability. For LDPE (a long-chain aliphatic polymer), ITIs yield lower conversion but higher selectivity to olefins than zeolites. • ITIs show enhanced resistance to coking during PS and LDPE cracking. • ITIs consistently outperformed mesoporous aluminosilicate Al-MCM-41, which lacked the required strong acidity, highlighting the advantages these solids made out of zeolite building units. • Operando FT-IR-GC-MS and TPO studies revealed how structural features like pore connectivity and acid strength influence deactivation, reaction mechanisms, and product distributions, underlining the value of rational ITI design based on polymer chemistry. Transformation (genetics) ; Waste management ; Environmental science ; Plastic waste ; Pulp and paper industry ; Business ; Chemistry ; Engineering Zeolite Catalysis and Synthesis ; Extraction and Separation Processes ; Chemical Synthesis and Characterization