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

Abstract

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 NiFe 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.