Efficient solvent- and hydrogen-free upcycling of high-density polyethylene into separable cyclic hydrocarbons

Ru nanoparticles on HZSM-5 catalysed solvent- and hydrogen-free upcycling of high-density polyethylene into a separable distribution of linear (C-1 to C-6) and cyclic (C-7 to C-15) hydrocarbons. Plastic pollution is a planetary threat that has been exacerbated by the COVID-19 pandemic due to the surge in medical waste, personal protective equipment and takeaway packaging. A socially sustainable and economically viable method for plastic recycling should not use consumable materials such as co-reactants or solvents. Here we report that Ru nanoparticles on zeolitic HZSM-5 catalyse the solvent- and hydrogen-free upcycling of high-density polyethylene into a separable distribution of linear (C-1 to C-6) and cyclic (C-7 to C-15) hydrocarbons. The valuable monocyclic hydrocarbons accounted for 60.3 mol% of the total yield. Based on mechanistic studies, the dehydrogenation of polymer chains to form C=C bonds occurs on both Ru sites and acid sites in HZSM-5, whereas carbenium ions are generated on the acid sites via the protonation of the C=C bonds. Accordingly, optimizing the Ru and acid sites promoted the cyclization process, which requires the simultaneous existence of a C=C bond and a carbenium ion on a molecular chain at an appropriate distance, providing high activity and cyclic hydrocarbon selectivity.

Automated summary

Ru nanoparticles on HZSM-5 catalyze solvent- and hydrogen-free upcycling of high-density polyethylene into separable linear (C-1 to C-6) and cyclic (C-7 to C-15) hydrocarbons. Plastic pollution, worsened by the COVID-19 pandemic, requires a sustainable and economically viable recycling method that avoids consumable materials. This study demonstrates the catalytic conversion of high-density polyethylene using Ru nanoparticles on HZSM-5, resulting in a separable distribution of linear and cyclic hydrocarbons.