Syngas and carbon nanostructures from pyrolysis-catalysis of nitrogen-containing plastics

This study investigated the pyrolysis-catalysis behavior of three representative nitrogen-containing plastics (polyamide 6 (PA6), polyurethane (PU), and polyacrylonitrile (PAN)) in the presence of a Ni/Fe bimetallic catalyst. The aim was to produce both product syngas (H2/CO) and multi-walled carbon nanotubes (CNTs). Several comprehensive analytical techniques, including thermogravimetric analysis, differential thermogravimetric analysis, gas chromatography/mass spectrometry, gas product analysis, scanning electron microscopy, high-resolution transmission electron microscopy, and temperature-programmed oxidation (TPO), have been used to examine their pyrolysis characteristics, volatile component compositions, syngas and hydrogen yields, and catalyst carbon deposition structures. The results showed that PA6 and PU produced high syngas yields (75.44%–77.97%, mass fracction), whereas PAN presented a higher H2/CO molar ratio and higher solid residue yield, indicating a greater tendency toward the formation of stable solid products during pyrolysis. In terms of the catalyst carbon deposition morphology, the pyrolysis volatiles from PA6 promoted the growth of well-structured multi-walled CNTs. PU mainly produced agglomerated graphitic carbon, and PAN formed a mixed structure containing bamboo-like CNTs and graphite layers. These morphological differences were further supported by TPO analysis, which revealed clear distinctions in the thermal stability of the resulting carbon structure. Overall, this work demonstrates the controlling role of the plastic molecular structure in influencing the distribution of pyrolysis products and the growth pathways of carbon materials. These findings provide theoretical support and an experimental basis for the resource utilization of nitrogen-containing polymers and the targeted synthesis of functional carbon nanomaterials.Graphical abstract