Complementary acid site mechanisms in hydrogen-free polyethylene upcycling: elucidating the distinct roles of Brønsted and Lewis sites in Ce-modified zeolites

초록

The environmental burden of petrochemical-derived plastics, particularly polyolefins such as polyethylene and polypropylene, has spurred the search for sustainable upcycling strategies. Conventional hydrogenolysis and hydrocracking processes rely on external H2, over 98% of which is produced via steam methane reforming or coal gasification; both methods yield significant CO2 emissions. In this study, we demonstrate a hydrogen-free approach to PE upcycling using zeolite Y ion-exchanged with various cations (Na+, Li+, K+, H+, La3+, and Ce3+). Among these, the Ce-exchanged mesoporous zeolite (Ce_meso_Y) achieved complete PE conversion with an 88.7% yield of naphtha-range hydrocarbons (C5-C12). NH3-TPD and pyridine-DRIFTS analyses revealed that Br & oslash;nsted acid sites (BASs) drive C-C bond cleavage, while strong Lewis acid sites (LASs) promote intramolecular hydrogen transfer from the polymer backbone, thereby eliminating the need for external H2. Extending this approach to post-consumer polyolefin waste (including HDPE bottles, LDPE film, and PP cases) delivered 70.5-82.6% conversion and 77.8-84.8% naphtha selectivity. Our findings establish a sustainable, hydrogen-free route for plastic upcycling by harnessing intrinsic polymer hydrogen and fine-tuning acid site functionality.

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