Nowadays, there is no doubt that our society benefits from plastic products for a great multitude of applications, including manufacturing, food safety, packaging, transportation, healthcare, and scientific research. Geyer et al. reported that as of 2015, approximately 6300 Mt of plastic waste had been generated, and annually more than 350 Mt were annually produced now. A large number of accumulated plastic waste was mainly attributed to the chemical and physical inertness of the plastics. Currently, the mechanical approach has been adapted for plastic recycling. However, a downfall of this method is that the recycled products have deteriorated material properties compared to virgin plastics, reduce the economic incentives for recycling. A potential solution is chemical recycling, or “upcycling,” which converts plastic waste into high-value industrial chemicals. Inspired by the processive enzyme in nature, a mesoporous shell/active site/core catalyst architecture (mSiO<sub>2</sub>/Pt/SiO<sub>2</sub>) was designed that has localized platinum nanoparticles at the interface of the core/shell. Solid-state NMR shows that with such MCM-41 type of pore geometry, polymers can be grabbed by the pore while maintaining essential mobility inside the pore. Catalytic hydrogenolysis employs this catalyst to deconstruct high-density polyethylene proved the processivity behavior from these aspects: (1). High-temperature gel permeation chromatography characterization of the solid remainder at 10% conversion shows intact properties compared to the virgin polymer. (2). Liquid products yielded from the reaction have a narrow distribution. (3). No intermediate product was discovered between the polymer molecular weight and liquid product peaks. Combining all these characterizations and catalytic evidence show that this inorganic catalyst design behaves similar to the processive enzyme.

Catalytic upcycling of high-density polyethylene via a processive mechanism

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ACS Fall 2022

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