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Polyethylene terephthalate (PET) can be recovered as high-purity bis(2-hydroxyethyl terephthalate) (BHET) monomer by glycolysis in the presence of Fe3O4 nanoparticles (NPs). In this study, Fe3O4 NPs of various shapes, sizes, and surface areas were synthesized using different colloidal synthesis methods, and the conversion of PET glycolysis and BHET yield were compared. Spinel ferrite NPs, including Fe3O4, were synthesized using the coprecipitation (CP), thermal decomposition (TD), and the hydrothermal (H) methods. Among the NP catalysts, Fe3O4-CP exhibited the best glycolysis performance with a PET conversion of ∼100% and BHET yield of 93.5% at 195 °C for 2 h owing to its high surface area (146.6 m2 g−1). The larger the surface area and the better the dispersion, the higher the glycolysis activity. The glycolysis performance of the mixed spinel ferrite NPs was similar to that of the Fe3O4 NPs, indicating that replacing Fe2+ in the Fe3O4 NPs with other transition metals, M2+, did not significantly change the glycolysis performance. BHET monomers produced from commercial waste PET bottles in large quantities contained trace amounts of metal contaminants, because PET production uses various metal-based additives and catalysts. Amberlite IRC-120, a cation-exchange resin, effectively removed metal impurities from BHET. This study provides an effective strategy for producing recycled PET (r-PET) by waste PET glycolysis. [ABSTRACT FROM AUTHOR]

Core@shell Ni@Co and bimetallic alloyed Ni–Co nanoparticles with controlled Co/Ni compositions were prepared and supported on CeO 2 to investigate their performance in catalytic dry reforming of methane (DRM) and occurrence of sintering and coking. Increasing the Co/Ni ratio significantly reduced coke deposition while maintaining catalytic activity for DRM. However, a Co/Ni ratio > 1 caused a rapid decrease in activity. The Ni@Co 1 /CeO 2 catalyst exhibited the highest CH 4 and CO 2 conversions, with long-term stability during DRM at 800 °C for 100 h. The initial core@shell structure of the Ni@Co 1 /CeO 2 catalyst transformed to a homogeneous alloy after DRM at 800 °C for 10 h, losing its Co shell. However, the bimetallic alloyed Ni–Co 1 /CeO 2 catalyst transformed into a non-uniform alloy rich in Co on the surface after DRM for 10 h. As the elemental distribution of the NPs becomes more homogeneous, Ni–Co 1 /CeO 2 exhibit similar catalytic activity to Ni@Co 1 /CeO 2 after 50 h. The oxygen vacancies on the CeO 2 surface provided oxygen atoms to the Ni surface, removing carbon species deposited and releasing CO. Therefore, Ni@Co 1 /CeO 2 catalyst provides excellent catalytic activity and stability due to the rapid formation of a homogenous alloy and the synergistic effect of Co and CeO 2. [Display omitted] • Core@shell Ni@Co nanoparticles with controlled Co/Nicompositions were prepared. • Ni@Co x /CeO 2 catalysts show high activity and stability in DRM. • The increased Co content of Ni@Co x /CeO 2 improves the coke resistance. • Ni@Co 1 /CeO 2 catalysts were transformed into a homogeneous NiCo alloy during DRM. [ABSTRACT FROM AUTHOR]