Methylcyclohexane-assisted polypropylene upcycling over PtRu/Al₂O₃ via tandem dehydrogenation-hydrogenolysis

Catalytic hydroconversion of polyolefin waste typically relies on the addition of high-pressure hydrogen, which greatly impacts both the process implementation and economic viability. Here we report polypropylene (PP) hydrogenolysis coupled to methylcyclohexane (MCH) dehydrogenation providing an external-H₂-free tandem route to naphtha-range liquid hydrocarbons. The best performing catalysis system was 1 nm sized PtRu nanoparticles (1 wt% Pt/1 wt% Ru) on γ-Al₂O₃. At 300 °C, this catalyst could facilitate over 96 wt% PP conversion with more than 88 wt% as naphtha-range liquid hydrocarbon products. This performance was retained over 6 recycles. Spectroscopic characterisation indicates the formation of electronically coupled PtRu domains, which promote MCH dehydrogenation and moderate C-C bond cleavage. Solvent screening shows that hydrocarbon liquids with different structures lead to pronounced differences in PP conversion and product selectivity. Molecular dynamics simulations of PP in representative solvents provide a qualitative picture of how solvent-dependent chain mobility and chain extension may influence polymer accessibility to catalytic sites. Techno-economic analysis and life-cycle assessment suggest that, under favorable feedstock assumptions, renewable MCH could lower both carbon intensity and production cost relative to a direct H₂-based route. These results identify MCH-assisted PtRu nanoparticle catalysis as a viable tandem process for PP upcycling and highlight the importance of coupling hydrogen-donor chemistry with liquid-phase transport effects in plastic waste valorisation.