Enhancing Hydrogen Production via Ex Situ Catalytic Fast Pyrolysis of Polypropylene with Upcycled Biochar-Supported FeAl₂O₄ Catalyst

The coupling of fast pyrolysis with green catalysis offers a sustainable approach for transforming waste polypropylene (PP) plastic into valuable hydrogen and carbon materials. The intrinsic catalytic activities of biochar, Al2O3@biochar, Fe3O4@biochar, Fe2AlO4@biochar, and FeAl2O4@biochar are explored for upgrading the fast pyrolysis vapors of PP powder. The FeAl2O4@biochar catalyst with tetrahedral iron sites achieves an excellent hydrogen yield, equivalent to 86.25 H% in PP. The hydrogen yield from converting practical PP mask waste reaches 57.98 ± 1.96 mmol gplastic–1, more than 673.61 ± 7.00 mmol gFe–1. The density functional theory (DFT) calculation indicates that a closer d-band center of FeAl2O4 is more favorable for C–H bond activation and that dehydrogenation of propylene as a model compound is the primary source of hydrogen production, more readily than C–C bond cleavage, and efficiently generates H2.