Effects of Catalytic Promoter Mn on Ni/ZSM-5 Catalyst to Catalyst Waste Plastic Syngas to Prepare Carbon Nanotubes for Co-Production of Hydrogen

Carbon nanotubes (CNTs) produced by catalytic reforming of the waste plastic syngas is a high value-added by-product of hydrogen production. Catalysts play an important role in the growth of carbon nanotubes. The influences of Ni/ZSM-5 catalyst, Ni–Mn/ZSM-5 catalyst and temperature were performed in a lab-scale tubular reactor. The catalysts and product carbon were analyzed by different characterization methods, including temperature-programed reduction/oxidation, X-ray diffractometer, scanning electron microscope, transmission electron microscope, X-ray energy spectrometer. The results showed that in the presence of Ni–Mn/ZSM-5 catalyst with the addition of catalytic promoter Mn, 650 °C was the optimum temperature during the operating temperature range of 600 °C~800 °C for the rate of carbon production and hydrogen production, and the carbon production was the highest, which was 2.95gCNTs/gCatalyst (wherein the Multi-walled carbon nanotubes (MWCNTs) were main product), and compared with the monometallic Ni/ZSM-5 catalyst, the Ni–Mn/ZSM-5 catalyst with Mn addition increased the H2 content in the syngas from 14 Vol.% to 39 Vol.%. The highest carbon nanotubes proportion of 95.81% to total carbon deposition was obtained under the conditions of 750 °C. The introduction of catalytic promoter Mn transforms the growth mode of carbon nanotubes from top growth mode to bottom growth mode, and obtains carbon nanotubes with more regular structure. It suggested that Ni–Mn/ZSM-5 catalyst had the potential for high quality carbon nanotubes and H2-riched gas production from waste plastic syngas.