Breaking the Yield-Selectivity Trade-Off in Polypropylene Upcycling via Ternary-Active ZnAlO Nanocomposites

Abstract

Plastic upcycling into iso-alkenes offers a sustainable route to mitigate plastic pollution and reduce the carbon footprint relative to petroleum-derived routes. However, selective C─C bond cleavage remains challenging, often resulting in broad product distributions and limited yields. Here, we report a tandem decomposition-catalysis strategy employing ternary-active ZnAlO catalysts for the selective conversion of polypropylene (PP) into narrow-range iso-alkenes. Zn₁₀AlO (10 wt% Zn proportion) achieved a liquid yield of 77.75 wt% with 83.71% selectivity toward C₈–C₁₂ iso-alkenes. The catalyst maintained liquid yield above 77 wt% and selectivity of ~84% toward narrow-range iso-alkenes over 10 successive cycles without catalyst regeneration. Furthermore, Zn₁₀AlO exhibited strong tolerance toward real-world PP waste, delivering product distributions comparable to those obtained from virgin PP. Structural and catalytic investigations revealed that the ternary-active ZnO─ZnAl₂O₄─Al₂O₃ nanocomposite, featuring balanced acidity and abundant oxygen vacancies, promoted controlled β-scission and isomerization while suppressing excessive cracking. Simply put, this work established a catalyst design strategy that integrated ternary-active nanocomposites and tailored acidity to overcome the yield-selectivity trade-off in PP upcycling and enabled the efficient production of value-added narrow-range iso-alkenes.