Methylcyclohexane-assisted polypropylene upcycling over PtRu/Al2O3via tandem dehydrogenation–hydrogenolysis

Abstract

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.