Calcium titanate mixed metal oxides with different contents were used as supports for
NiMo catalyst prepared by the sol–gel method. The activities of these catalysts were tested in
the catalytic decomposition of waste polypropylene (PP) for the synthesis of carbon nanotubes
(CNTs) using a single-stage chemical vapor deposition technique. The physico-chemical properties
of the catalysts and deposited carbon over the catalysts were checked by X-ray diffraction (XRD),
scanning electron microscopy (SEM), temperature-programmed reduction (TPR), N2 physisorption,
transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis
(TGA). The TEM and XRD results presented a high dispersion of the active metal species on the
surface of the support materials. The result showed that increasing the support content led to an
increased crystallite size of the catalysts and a resultant reduction in CNTs yield from 44% to 35%.
NiMo-supported CaTiO3 catalyst displayed good catalytic activity and stability toward CNTs growth.
Furthermore, the effect of calcination temperature on the morphology, yield, and quality of CNTs was
also studied, and it was observed that thermal treatment up to 700 ◦C could produce well graphitized,
high-quality, and high-yield CNTs from the waste PP.