Long-lived metal-zeolite catalysts for polyolefin aromatization via synergistic tandem dehydroaromatization and hydrogenolysis

Abstract

Converting waste plastics directly into valuable aromatic chemicals is a promising, cost-effective recycling strategy. Traditional zeolite-catalyzed cracking of polyolefins to produce aromatics often needs high temperatures and faces issues like low selectivity for liquid aromatics, separation difficulties, and rapid catalyst deactivation due to coking. To address this, a multifunctional Ni/HZSM-5 catalyst was developed to efficiently upgrade various polyolefins—including polyvinyl chloride—into gaseous alkanes (C₁–C₅) and easily separable liquid aromatics (C₆–C₁₂) at 400 °C, without added solvents or hydrogen. Aromatic products make up 57.1 wt% of total output, with more than 97.8 % selectivity for the liquid phase and a BTX (benzene, toluene, and xylene) selectivity of 76.1 %. The high activity and selectivity for aromatics stem from synergistic interactions between Ni nanoparticles (NPs) and acid sites in the zeolite, which promote selective C–C bond breaking and control hydrogenolysis and aromatization pathways. This synergy allows precise control over the distribution of products by carbon number and favors the formation of separable aromatics. Notably, the catalyst also prevents coking by hydrogenolyzing and hydrogenating reactive intermediates before they form stable graphite-like deposits. Consequently, Ni/ZSM-5 catalyst demonstrates excellent stability, maintaining consistent aromatics yield over 13 consecutive cycles and processing over 30 times its weight in plastics without regeneration. After regeneration, the activity of the catalyst was fully restored, highlighting its potential for industrial use. This work offers valuable insights for designing durable, high-activity catalysts, providing a practical route to improve plastic recycling technologies.