Catalytic Pyrolysis of High-Density Polyethylene for Single-Walled Carbon Nanotubes on Fe/MgO

Abstract

The large-scale consumption and low recycling rate of plastics necessitate effective chemical recycling solutions. High-density polyethylene (HDPE) serves as an ideal carbon source for synthesizing high-value carbon materials such as carbon nanotubes. In this study, a powdered Fe/MgO catalyst was prepared to convert the HDPE into high-quality SWCNTs in a two-stage reactor. Concurrently, reactive force field molecular dynamics simulations elucidated the adsorption, cracking, and carbon diffusion behaviors of pyrolytic intermediates on the Fe surface, along with the kinetics of iron carbide formation. The results demonstrate that Fe/MgO efficiently converts HDPE into SWCNTs, achieving a maximum yield of 33.7% with 1 g of the catalyst containing 2 wt % Fe at 900 °C. The catalyst preferentially adsorbs olefins such as ethylene, suppresses the polymerization and cyclization of small molecules, and thereby promotes SWCNT growth. The high efficiency of the Fe/MgO catalyst is attributed to a unique high-temperature inversion of its spinel structure, which triggers Fe3+ migration from the bulk to the surface. This work not only presents a high-value route for plastic waste utilization but also provides atomic insights into SWCNT synthesis from HDPE using Fe/MgO.