Plastic Upcycling on Hierarchical FAU Catalysts: Influence of Mesopore Identity and Connectivity

Abstract

Mismanagement of plastic waste presents significant environmental challenges, with only a small fraction of plastic being recycled and a majority ending in landfills or natural environments. To address these concerns, this study explores catalytic upcycling of polyolefin plastics using hierarchical FAU-type zeolite catalysts. Specifically, it investigates how mesoporous structures within FAU catalysts influence catalytic cracking performance, which is essential for converting bulky plastic polymers into economically valuable hydrocarbons. Four distinct hierarchical FAU materials were synthesized via varied post-synthetic desilication methods, each generating unique mesoporous networks characterized through X-ray diffraction, N2-physisorption, and acidity measurements via temperature-programmed desorption. Catalytic cracking reactions of polyethylene (PE), polypropylene (PP), and hexatriacontane (C36) were conducted to evaluate performance differences attributable to mesopore size, volume, and connectivity. Results revealed significant improvements in cracking rates for catalysts synthesized with surfactants (H-FAU-CTA, H-FAU-TPA), while hydrothermally treated catalysts showed enhanced reactivity specifically for larger, branched PP molecules, suggesting that mesopore accessibility and geometry significantly modulate catalytic efficacy. Importantly, the presence of mesopores alone did not universally enhance reaction rates; instead, performance depended critically on mesopore characteristics and reactant molecular size. These findings demonstrate the nuanced relationship between hierarchical porosity and catalytic activity, emphasizing the importance of targeted mesopore design for optimizing plastic waste upcycling processes. The insights gained lay foundational knowledge for developing advanced catalysts that could significantly improve environmental sustainability and facilitate a circular economy for plastics.