<p>Polyolefins represent the largest fraction of global plastic waste, yet their chemical inertness poses a major challenge for recycling. In this study, normal‑alkane modeling was employed to investigate the catalytic transformation of linear alkyl chains over two Pt‑modified zeolites, Pt/USY and Pt/ZSM‑5, using n‑dodecane and n‑nonane as representative long‑ and short‑chain analogs. Comprehensive characterization revealed that Pt dispersion and zeolite pore topology jointly modulate acidity and metal-acid synergy, thereby steering product selectivity and reaction pathways. Pt/USY, with its larger pore volume and moderate acidity, promoted dehydrogenation and cracking, yielding higher fractions of alkenes and branched alkanes while suppressing excessive aromatization. In contrast, Pt/ZSM‑5 exhibited stronger hydrogenation activity, converting olefinic intermediates into saturated alkanes and cycloalkanes while reducing aromatic formation. Comparative analysis of n‑dodecane and n‑nonane demonstrated that longer alkyl chains undergo deeper cracking and secondary reactions, leading to higher yields of light hydrocarbons, aromatics, and coke, whereas shorter chains are less reactive and more resistant to cyclization. Both Pt‑modified catalysts showed reduced coke deposition relative to their parent zeolites. These findings provide mechanistic insights into Pt–zeolite synergy and chain‑length effects, offering guidance for the rational design of advanced catalysts to enable efficient chemical recycling of polyolefin wastes into tailored fuels and chemicals.</p> Graphical Abstract <p></p>