Impact of temperature on the activity of Fe-Ni catalysts for pyrolysis and decomposition processing of plastic waste

Abstract Thermal chemical processing of plastic has been seen as an efficient practice for the disposal and resource utilization facing the current plastic waste problem. A pyrolysis followed by catalytic decomposition process was investigated in this work to produce carbon materials from polypropylene plastic over FeNi catalysts. The effects of both catalysis temperature (600, 700 and 800 °C) and catalyst type on the gaseous yields, as well as the physicochemical properties (morphology, porosity, purity and graphitization degree) of the as-obtained carbon materials were systematically explored. Various technologies including high resolution electron microscopies, temperature programmed oxidation, Raman, X-ray diffraction were used for full characterizations of the as-obtained carbons. Results show that the yields of both carbon and hydrogen gas were significantly proportional to the catalysis temperature. In terms of the physiochemical properties of carbon materials, the low catalysis temperature of 600 °C generated the majority amorphous and disordered carbons, due to the insufficient decomposition reactions and low catalyst activity. Catalysis temperature higher than 700 °C was necessary for the successful growth of carbon nanotubes, while further increase in temperature mainly acted on the yield rather than thermal stability and graphitic degree. High purity multi-walled carbon nanotubes with outer diameters of 20–30 nm and length up to few micrometers were generated with FeNi1 at 800 °C. FeNi1 catalyst synthesized by sol–gel method displayed higher activity towards the production of high quality carbon materials than FeNi2 catalyst at any temperature range investigated, due to the porous structure and the uniform dispersion of metal particles.