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

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 g  1 LDPE, 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.