Pyrolysis and in-line catalytic decomposition of polypropylene to carbon nanomaterials and hydrogen over Fe- and Ni-based catalysts

Thermo-chemical conversion of waste plastics into clean energy and valuable products can be a promising technology from both economic and environmental perspectives. In this work, pyrolysis and in-line catalytic decomposition of polypropylene was performed for production of hydrogen and carbon nanomaterials. A series of novel Fe/Ni catalysts were prepared, and the effects of catalyst active metal component (Fe, Ni, FeNi) and synthesis method (sol–gel and impregnation) were explored. Results show that the production of hydrogen and solid products was in a descending order as Fe-Ni, Fe and Ni loading, while sol–gel prepared catalysts were more catalytic effective than their impregnated counterparts. FeNi(SG) exhibited an optimal activity with productions of 25.14 mmol/gplastic of hydrogen and 360 mg/gplastic of high quality carbon nanomaterials, which was attributed to (i) uniform mesoporous structure with 212.30 m2/g specific surface area (ii) high dispersion degree (42.02%) of active metals and (iii) enhanced reducibility originated from the synergistic effect between Fe and Ni. Carbon nanomaterials which contained the majority of carbon nanotubes were comprehensively characterized in terms of structure complexity, morphology and graphitization degree, and the formation mechanism of bamboo-like multi-walled carbon nanotubes from pyrolysis and catalytic decomposition of polypropylene was also discussed.