Effects of Nickel Species on Ni/Al2O3 Catalysts in Carbon Nanotube and Hydrogen Production by Waste Plastic Gasification: Bench- and Pilot-Scale Tests

Upcycling waste plastics into carbon nanotubes (CNTs) and hydrogen is attractive for its efficient disposal. Although Ni-based catalysts are typically used in both hydrogen production and CNT synthesis, few studies have investigated the catalytic active site for the co-production of CNTs and hydrogen by waste plastic gasification. To evaluate the effect of nickel species distribution of the Ni/Al2O3 catalyst, it was prepared by an impregnation method using different calcination atmospheres to determine their feasibility for the co-production of CNTs and hydrogen. For comparison, various Ni/Al2O3 catalysts for CNT growth were examined by CH4 thermal chemical vapor deposition (CVD). Ni/Al2O3 calcined under a reductive H2 atmosphere (H–Ni/Al2O3) gave smaller nickel nanoparticles containing metallic nickel species, which showed optimal performance for CNT and hydrogen co-production by waste plastic gasification. In addition, the quality of the CNTs was higher using this process compared to the CNTs synthesized by CH4 thermal CVD. Further examination of the catalysis temperature found that the H–Ni/Al2O3 catalyst gave higher quality CNTs in a 24.3% yield, along with a hydrogen production rate of 325.4 mmol h–1 g–1 of catalyst at 680 °C. The produced H–Ni/Al2O3 contained metallic nickel, demonstrating an improved catalytic activity for CNT and hydrogen production from waste plastics.