H-ZSM-5 Catalysts for the catalytic upcycling of polypropylene glycol

Without effective management, the steady increase of waste plastics threatens environmental well-being and ecological balance. Plastic up/recycling is a promising solution but has many challenges. In this work, catalytic cracking of polypropylene glycol (PPG) was investigated at varying reaction temperatures of 350–550 °C under nitrogen and steam, using H-ZSM-5 zeolites with different silica-to-alumina (SiO₂/Al₂O₃) ratios of 23:1 and 50:1. The catalysts were assessed through physisorption, chemisorption, solid-state magic-angle spinning nuclear magnetic resonance spectrometry, thermogravimetry, electron microscopy, and positron annihilation lifetime spectroscopy. Extra framework aluminum and Lewis-to-Bronsted acid site ratios were found to play a significant role in the selectivity towards propionaldehyde, where values ∼ 80 % could be reached. In addition, a possible pathway for the PPG cracking reaction was proposed, which may lead to a better understanding of PPG and waste plastic decomposition via zeolite-based catalysts.