Catalytic pyrolysis of oxygen-containing waste polycarbonate for the preparation of carbon nanotubes and H₂-rich syngas

In this study, ex-situ catalytic pyrolysis of oxygen-containing polycarbonate (PC) was conducted to prepare carbon nanotubes (CNTs) and H₂-rich syngas. This study examined the influence of the active metal components (Ni and Fe), catalyst pre-reduction, and pre-deoxygenation of pyrolysis volatiles on the catalytic performance and mechanism. Results show that the reductive constituents in pyrolysis volatiles make it difficult to reduce the Fe oxides, thus hindering the CNTs growth on Fe catalysts, compared to Ni catalysts. H₂ pre-reduction of Ni and Fe catalysts enhances the generation of CNTs and syngas. The pre-reduced Fe catalyst exhibits better carbon deposit performance, reaching 263 mg/g_plastics. The pre-reduced Ni catalyst better facilitates the reforming reaction of CO₂ and H₂O, resulting in higher syngas yields of 32.75 mmol/g_plastics, with a volume proportion of 94.4 vol%. The addition of the deoxygenation catalyst Ni/HZSM-5 promotes the growth of CNTs with fewer defects and higher graphitization on Ni catalysts. The excess CO₂ and H₂O generated by the introduction of Ni/HZSM-5 may oxidize the Fe⁰ on pre-reduced Fe catalysts, inhibiting the growth of CNTs. The mechanism of the growth of CNTs and syngas from PC is also explored. The findings can provide theoretical guidance for the disposal of waste plastics.