Influence of zeolite hydrophilicity and hydrophobicity on water-assisted polyethylene hydrocracking

Abstract

The catalytic upcycling of polyethylene (PE) remains a major challenge in sustainable waste management. This study demonstrates that water promotes PE hydrocracking over Ru/zeolite catalysts only when the support framework is strongly hydrophilic, as in HY and HMOR. Systematic characterization reveals that this promotional effect is governed by surface wettability, rather than acidity or metal dispersion. Thermodynamic analysis confirms that water and PE are immiscible under reaction conditions, ruling out direct water–polymer interactions. Instead, water preferentially associates with hydrophilic catalyst surfaces, promoting Brønsted acid activity through confined hydration. Controlled experiments show that direct contact between water and the catalyst is essential for enhanced reactivity; spatial separation between the two leads to suppressed conversion, likely due to unfavorable interactions between water and the molten polymer. These findings highlight the mechanistic role of interfacial water–catalyst accessibility and establish catalyst hydrophilicity as a key design parameter for reliable and efficient water-assisted hydrocracking. The results have practical implications for processing moisture-containing plastic waste streams.