Temperature-Dependent NiFeAl catalysts for efficient microwave-assisted catalytic pyrolysis of polyethylene into value-added hydrogen and carbon nanotubes

Abstract

Polyolefins, comprising the majority of disposable plastics, face challenges in catalytic upcycling due to their inert saturated C(sp3)-C(sp3) bonds. This work demonstrates microwave-assisted catalytic pyrolysis, demonstrating the direct conversion of low-density polyethylene (LDPE) into valuable H2 and multi-walled carbon nanotubes (MWCNTs) over a porous ternary NiFeAl-T composite catalyst that serve as a microwave absorber. Optimizing the calcination temperature promoted metal nanoparticle dispersion, leading to enhanced catalytic performance. Specifically, lower temperatures favored metal–metal interactions, inducing porous architectures with superior microwave absorption and energy dissipation capabilities. This facilitated cleavage of C–C and C–H bonds in LDPE during microwave irradiation. An optimal NiFeAl-450 catalyst achieved a maximum H2 yield of 60.5 mmol gLDPE-1, with an H2 concentration of 85.1 vol% in gas products, alongside high-value MWCNTs. Moreover, successive recycling test displayed stable H2 and MWCNTs yields from LDPE. This work elucidates a promising pathway for upcycling plastic waste via microwave-assisted catalytic pyrolysis.