Synthesis of bimetallic NiMo/MgO catalyst for catalytic conversion of waste plastics (polypropylene) to carbon nanotubes (CNTs) via chemical vapour deposition method

Non-biodegradable waste plastics constitute huge environmental problem and their effective disposal or beneficiation to value-added products such as carbon nanotubes (CNTs) is imperative for environmental sustainability. However, methods employ in the preparation of the catalysts employed in the catalytic conversion of waste plastics to CNTs play a key role in providing the desired nanoparticle morphology and stability towards increasing the catalytic (active) sites for nucleation and growth of carbon nanotubes (CNTs). It also determines the diameter, nature and alignment of the produced CNTs. In this study, bimetallic NiMo supported on MgO catalyst was prepared by two different synthesis methods: sol-gel and incipient wet impregnation (IWI) methods. Physico-chemical property and catalytic activity of the catalysts obtained from these catalyst preparation methods were evaluated and compared during the synthesis of CNTs from waste polypropylene under similar conditions using a one-step chemical vapour deposition technique (CVD). The physico-chemical properties of the prepared catalysts and those of the produced CNTs were obtained via X-ray diffraction (XRD) and Scanning electron microscopy (SEM) and compared. Results reveal that all prepared catalysts are porous and exhibited catalytic activity, but the catalyst obtained via IWI method is more porous and displayed higher catalytic activity when compared to the one obtained via sol-gel. Furthermore, bulk deposition of multi-walled CNTs (MWCNTs) of different diameters was also observed.