(674a) Waste Polypropylene Conversion to Lubricant Using Cheap Earth-Abundant Bimetallic Catalysts

Polyolefins (PO), such as polypropylene (PP) and polyethylene (PE), are the dominant components of single-use packaging and account for ~70% of plastic waste in the U.S.¹ Catalytic upcycling provides a promising route to convert waste POs into higher-value products such as lubricants, waxes, and surfactants.²˒³ For instance, hydrogenolysis of PP over Ru/TiO₂ under high H₂ pressure yields high-viscosity lubricants at ~75% selectivity in just 6 hours at 250 °C.³˒⁴

However, large-scale application remains limited due to the high cost of noble metal catalysts and long reaction times. In this work, we present a cost-effective strategy based on bimetallic catalysts composed of earth-abundant metals doped with small amounts of Ru. These catalysts show enhanced hydrogenolysis activity and significantly reduced reaction times, offering a scalable solution for plastic waste valorization.

To understand catalyst behavior under realistic conditions, we employed a suite of in situ techniques—transmission electron microscopy (TEM), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and infrared (IR) spectroscopy. These tools revealed the dynamic formation of metastable metal–metal–oxide interfaces in the bimetallic particles under reactive, polymer-melt conditions. These interfaces exhibit higher catalytic activity than fully reduced metal particles, enabling faster and more selective PO conversion.

This structure–reactivity relationship is consistent across multiple bimetallic systems and echoes recent findings in CO₂ hydrogenation catalysts,⁵ suggesting a shared underlying mechanism involving dynamic metal–oxide interactions in condensed-phase environments.

Our findings provide a mechanistic framework for designing low-cost, earth-abundant catalysts for hydrogenolytic upcycling of polyolefin plastic waste, with broad implications for sustainable chemical manufacturing.

References

(1) Milbrandt et al. Res., Cons. Recycl. 2022, 183, 106363.

(2) Hernández et al. ACS Sust. Chem. Eng. 2023, 11 (18), 7170-7181.

(3) Kots et al. ACS Catalysis 2021, 11 (13), 8104-8115.

(4) Kots et al. Nat. Comm. 2022, 13 (1), 5186.

(5) Parastaev et al. Nature Catalysis 2022, 5 (11), 1051-1060.