Abstract:
The role of the effect of the support on the reactivity of heterogeneous catalysts cannot
be over-emphasized. Therefore, the study documented in this article investigated the effect of
different metal oxide supports (MgO, CaO and TiO2
) and mixed oxide supports (CaTiO3
) on the
performance of a bimetallic NiMo catalyst prepared via the sol–gel method during the catalytic
growth of carbon nanotubes (CNTs) from waste polypropylene (PP). Waste PP was pyrolyzed at
700 ◦C in a single-stage chemical vapor deposition reactor and off-gas was utilized in-situ as a
cheap carbon feedstock for the growth of CNTs under similar conditions for all the prepared NiMo
catalysts (supported and unsupported). The structures of the prepared catalysts and deposited
carbon were extensively characterized using X-ray diffraction (XRD), temperature-programmed
reduction (TPR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc.
The catalytic performance of NiMo supported and unsupported catalysts was evaluated in terms of
the yield, purity, and morphology of synthesized CNTs. The results revealed that the stabilizing role of
supports is fundamental in preventing nanoparticle agglomeration and aggregation, thereby resulting
in improved yield and quality of CNTs. Supported NiMo catalysts produced better aligned graphitic
and high-quality CNTs. The NiMo/CaTiO3 catalyst produced the highest carbon of 40.0%, while
unsupported NiMo produced low-quality CNTs with the lowest carbon yield of 18.4%. Therefore,
the type of catalyst support and overall stability of catalytic materials play significant roles in the
yield and quality of CNTs produced from waste PP.
