Enhancement of hydrogen and carbon nanotubes production from hierarchical Ni/ZSM-5 catalyzed polyethylene pyrolysis

Abstract

Pyrolytic catalysis technology has been considering a promising strategy to convert waste plastics into high-value products from economic and environmental perspectives. The design of efficient catalysts plays a key role in product distribution. In this study, Ni-supported hierarchical ZSM-5 (designated as Ni/ZSM-5-M) was developed for the pyrolytic catalysis of polyethylene (PE) to produce carbon nanotubes (CNTs) and hydrogen by using two-stage fixed bed reactor. Results showed that the Ni/ZSM-5-M catalyst generated the highest carbon material yield of 43.8 wt% and the maximum hydrogen production of 5.2 wt% about 26.27 mmol/gPE. In order to understand the correlation between catalysts structure and products, the essential structural characteristics of as-prepared catalyst were characterized by the comprehensive approach such as SEM, TEM, XRD, TPR and so on. The results indicated that alkali treatment introduced a hierarchical structure and significantly improved the dispersion of Ni particles, producing a catalyst surface area of 356 m2/g and average Ni particle size of ∼14.8 nm, which further enhancing catalytic activity for the production of hydrogen and CNTs. The Ni/ZSM-5-M catalyst produced a higher yield of carbon deposits (43.8 wt%), including over 66% high-value CNTs (289 mg/gPE) and hydrogen yield (5.2 mg/gPE). This study suggests alkali modification method to prepare Ni/ZSM-5-M catalyst is a promising way to promote the production of valuable CNTs and hydrogen from waste plastics.