Hydrogen-rich syngas production by pyrolysis-catalytic steam reforming of waste plastic over metal-loaded carbon catalysts

The pyrolysis-catalytic steam reforming of waste plastic offers a promising route for the sustainable production of hydrogen-rich syngas. In this study, a series of carbon-supported metal catalysts (Zn/C, Cu/C, and Fe/C) with a nominal metal loading of 5 wt% were prepared and systematically evaluated for the pyrolysis-catalytic steam reforming of high-density polyethylene in a two-stage reactor system. The structural evolution of fresh and used catalysts was comprehensively characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, and N2 physisorption analyses. The carbon support provides a porous and thermally stable framework that enables uniform metal dispersion and minimizes structural interference, allowing the catalytic roles of different metal species to be systematically evaluated. The results demonstrate that metal species distinctly regulate product distribution, carbon conversion pathways, and hydrogen potential, following the order of Fe/C > Cu/C > Zn/C. Density functional theory (DFT) calculations reveal that these differences originate from the coupled effects of hydrocarbon activation and water dissociation on metal surfaces. This work establishes a clear structure-performance-mechanism relationship and provides mechanistic insights for the rational utilization of metal-containing waste-derived char catalysts in pyrolysis-catalytic steam reforming systems.