Pyrolysis–Catalytic Reforming/Gasification of Waste Tires for Production of Carbon Nanotubes and Hydrogen

The production of high-value carbon nanotubes and hydrogen from the two-stage pyrolysis–catalytic reforming/gasification of waste tires have been investigated. The catalysts used were Co/Al₂O₃, Cu/Al₂O₃, Fe/Al₂O₃, and Ni/Al₂O₃. The pyrolysis temperature and catalyst temperature were 600 and 800 °C, respectively. The fresh catalysts were analyzed by temperature-programmed reduction and X-ray diffraction. The product gases including hydrogen were analyzed by gas chromatography, and the carbon nanotubes were characterized by scanning and transmission electron microscopy and Raman spectrometry. The results showed that the Ni/Al₂O₃ catalyst produced high-quality multi-walled carbon nanotubes along with the highest H₂ yield of 18.14 mmol g⁻¹ tire compared to the other catalysts, while the Co/Al₂O₃ and Cu/Al₂O₃ catalysts produced lower hydrogen yields, which is suggested to be associated with the formation of amorphous-type carbons on the surface of the Co/Al₂O₃ and Cu/Al₂O₃ catalysts.