In situ grown metallic nickel from X–Ni (X=La, Mg, Sr) oxides for converting plastics into carbon nanotubes: Influence of metal–support interaction

Abstract

The process of pyrolysis and in-line catalysis was employed for converting plastics into value-added carbon nanotubes (CNTs). The metallic nickel catalysts Ni/X (X = La, Mg, Sr) were prepared through in situ growth from parent X–Ni oxides under reductive conditions and used for the catalytic synthesis of CNTs. The results showed that the activities of nickel catalysts decreased in the order of Ni/La > Ni/Sr > Ni/Mg, which strongly depended on the degree of metal–support interaction. The strong metal–support interaction in Ni/Mg catalyst was not favorable for the exsolution of large amount of metallic Ni, resulting in the lowest yield of CNTs. On the other hand, the weak metal–support interaction in Ni/Sr was unfavorable for the high coverage of Ni nanoparticles, leading to the simultaneous growth of carbon nano-onions and CNTs. The Ni/La catalyst with moderate metal–support interaction exhibited the highest yield of CNTs due to optimized amount, size and surface coverage of Ni nanoparticles. The microstructure, graphitization degree, quality and purity of obtained carbon products were characterized using X-ray diffraction, electron microscopy, Raman spectroscopy and thermogravimetric analysis. This study demonstrated an effective and delicate approach to tune the supported metal nanoparticles, leading to enhanced catalytic activity.