Mitigation effects and mechanism of cycle-derived carbon nanotubes on hydrogen production from oxygen- and chlorine- containing plastics mixtures in microwave catalysis

Plastic pollution presents severe environmental challenges, necessitating sustainable waste-management system. This study investigated hydrogen conversion from various plastic mixtures—polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET)—via microwave thermal processing with a Ni-Al-Fe catalyst. Hydrocarbon plastics (PP/PE/PS) yielded 49.17 mmol/g hydrogen with ∼90 vol% purity, comparable to that of linear plastic, demonstrating negligent effects of aromatic structure on hydrogen yields. PET addition significantly reduced hydrogen due to oxygenated-intermediates inhibition effects active sites and oxidation of aluminum. Similarly, PVC decreased yields as chlorine induced metal migration and catalyst surface damage. Cycle-generated carbon nanotubes (CNTs) from plastic mixtures were used to mitigate the unfavorable effects. The modified catalyst (Ni-Al-Fe-CNTs) achieved 35 % higher hydrogen yields for both oxygen- and chlorine- containing plastics mixtures. This is attributed to enhanced surface strain, electrical structures, and adsorption of intermediates from CNTs, preserving coordination environment and enabling partial Ni and Fe reduction to form heterojunctions and oxygen vacancies. This study developed a circular economy model for managing plastic waste and high-value energy conversion.