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