Carbon nanotubes production from catalytic pyrolysis of polyethylene over nickel-based catalysts: The influence of support materials

•Different supports Ni-based catalyst was prepared for polyethylene pyrolysis.•The Ni/Al2O3 show excellent selectivity for carbon nanomaterials (36.5%).•The carbon nanotubes have high purity and graphitization degree.•The Ni/Al2O3 had abundant pore structure and moderate MSI.•More fishbone like carbon nanofibers were obtained from Ni/TiO2.