Investigating the influences of metal-support interaction in Ni[sbnd]Fe catalysts on the quality of carbon nanomaterials from waste polypropylene

Pyrolysis-catalysis is a promising method to realize the recycling of waste plastic. Thereinto, metal-support interaction (MSI) has a crucial impact on the properties and performances of catalysts. Different active metal components (Ni or/and Fe) and pre-reduction process were introduced to adjust the metal-support interaction in this work. The results showed that moderate MSI was obtained from NiFe while Ni presented the weaker MSI and a stronger one was revealed for Fe. After pre-reduction, the promotion of MSI was observed for all catalysts, leading to the increase of active metal particle size. For the carbon deposition process, a higher CNMs yield (44.4 wt%) was obtained from NiFe, followed by 30.0 wt% of Fe and 18.2 wt% of Ni. The moderate MSI and synergistic effects of two metal species contributed to the CNMs production. However, different results were observed after fresh Ni[sbnd]Fe catalysts were reduced. Less carbon was formed on reduced monometallic Fe or bimetallic NiFe catalyst. This might be ascribed to the stronger MSI promoted by the pre-reduction of Fe-containing catalysts, inhibiting the catalyst activity. In addition, the strengthened MSI made the CNMs growth mechanism shift from tip-model to base-model and the graphitization degree of CNMs was also decreased. Our study may provide specific guidance for the production of high-valued CNMs recycling from waste plastics.