Upcycling heteroatoms-containing plastics via bimetallic synergistic catalysis: Unveiling the role of O and Cl in C-H bond cleavage

[Display omitted] •Heteroatoms (O and Cl)-containing plastics were upcycled for H2-rich gas and carbon production.•Fe-Co/HY in Ar showed a synergistic effect on H2 production (>41 mmol/gplastic).•Ternary PE-PET-PVC had the higher hydrogen efficiency (91.40%) than individuals.•NiO and NiAl2O4 on the catalyst reacted with PVC-derived Cl· or HCl, yielding NiCl2.•Ni-Fe/HY in CO2-mediated pyrolysis-catalysis showed the highest H2 efficiency (62.34%). Given the complicated compositions and hazards of heteroatoms-containing plastics, the efficient upcycling remains a huge challenge. Herein this work proposed an innovative route via dual-stage pyrolysis-catalysis platform to upcycle heteroatoms-containing plastics for high-purity H2 and carbon nanotubes (CNTs) production. Among HY-supported metallic catalysts, bimetallic Fe-Co/HY achieved the maximum H2 yield (41.25 mmol/gplastic) and selectivity (71.76 vol%), alongside the carbon production of 520 mg/gplastic, revealing a catalytically synergistic effect between Fe and Co. Of the plastic individuals/combinations, the plastic combination (PW2) revealed the highest hydrogen efficiency (87.03 %) and H2 efficiency (49.71 %). Regarding the interactions among polyolefins, polyesters, Cl-containing plastics, ternary plastics (PE-PET-PVC) exhibited the higher H2 yield (35.33 mmol/gplastic), hydrogen efficiency (91.40 %), and H2 efficiency (49.14 %) than individual counterparts. The CNTs yield and purity gained from ternary PE-PET-PVC even outperformed these results obtained from individual PE (yield: 326.7 mg/gplasticvs 323.9 mg/gplastic; purity: 93.5 % vs 90.3 %). That was because the chlorinated aryloxy radicals generated from PVC and PET facilitated the cleavage of C (sp3)-H bonds, thereby enhancing the hydrogen extraction and carbon formation. Besides, NiO and NiAl2O4 on the catalyst were converted into NiCl2 by PVC-derived Cl· or HCl, subsequently being reduced into reactive Ni0. Additionally, bimetallic Ni-Fe/HY during CO2-mediated pyrolysis-catalysis displayed the highest H2 yield (55.67 mmol/gplastic), syngas purity (82.39 %), H2 efficiency (62.34 %), and CNTs yield of 367 mg/gplastic, reflecting an apparent synergistically catalytic effect between Ni and Fe. Overall, this study provides a superb solution in heteroatoms-containing plastics upcycling and greenhouse gas emission management.