The use of Ni-Fe catalysts for the catalytic pyrolysis of real-world waste plastics to produce hydrogen and high value carbon nanotubes (CNT), and the influence of catalyst composition and support materials has been investigated. Experiments were conducted in a two stage fixed bed reactor, where plastics were pyrolysed in the first stage followed by reaction of the evolved volatiles over the catalyst in the second stage. Different catalyst temperatures (700, 800, 900 °C) and steam to plastic ratios (0, 0.3, 1, 2.6) were explored to optimize the product hydrogen and the yield of carbon nanotubes deposited on the catalyst. The results showed that the growth of carbon nanotubes and hydrogen were highly dependent on the catalyst type and the operational parameters. Fe/γ-Al2O3 produced the highest hydrogen yield (22.9 mmol H2/gplastic) and carbon nanotubes yield (195 mg g−1plastic) among the monometallic catalysts, followed by Fe/α-Al2O3, Ni/γ-Al2O3 and Ni/α-Al2O3. The bimetallic Ni-Fe catalyst showed higher catalytic activity in relation to H2 yield than the monometallic Ni or Fe catalysts because of the optimum interaction between metal and support. Further investigation of the influence of steam input and catalyst temperature on product yields found that the optimum simultaneous production of CNTs (287 mg g−1plastic) and hydrogen production (31.8 mmol H2/gplastic) were obtained at 800 °C in the absence of steam and in the presence of the bimetallic Ni-Fe/γ-Al2O3 catalyst.
The authors wish to express their sincere thanks for the financial support from the National Natural Science Foundation of China (51622604), the China Postdoctoral Science Foundation (2016M602293) and the Foundation of State Key Laboratory of Coal Combustion (FSKLCCB1610). The experiment was also assisted by the Analytical and Testing Center in Huazhong University of Science & Technology (http://atc.hust.edu.cn, Wuhan 430074 China), and the Analysis Laboratory in the School of Chemical and Process Engineering at the University of Leeds. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowski-Curie grant agreement No. 643322 (FLEXI-PYROCAT).
- Ni-Fe catalyst
- Carbon nanotubes