Synthesis of biomass-derived N-doped porous carbon for energy storage and catalysis applications is a sustainable and environmentally friendly approach.

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Upcycling waste plastics into carbon nanotubes (CNTs) and hydrogen is attractive for its efficient disposal. Although Ni-based catalysts are typically used in both hydrogen production and CNT synthesis, few studies have investigated the catalytic active site for the co-production of CNTs and hydrogen by waste plastic gasification. To evaluate the effect of nickel species distribution of the Ni/Al 2 O 3 catalyst, it was prepared by an impregnation method using different calcination atmospheres to determine their feasibility for the co-production of CNTs and hydrogen. For comparison, various Ni/Al 2 O 3 catalysts for CNT growth were examined by CH 4 thermal chemical vapor deposition (CVD). Ni/Al 2 O 3 calcined under a reductive H 2 atmosphere (H−Ni/Al 2 O 3 ) gave smaller nickel nanoparticles containing metallic nickel species, which showed optimal performance for CNT and hydrogen co-production by waste plastic gasification. In addition, the quality of the CNTs was higher using this process compared to the CNTs synthesized by CH 4 thermal CVD. Further examination of the catalysis temperature found that the H− Ni/Al 2 O 3 catalyst gave higher quality CNTs in a 24.3% yield, along with a hydrogen production rate of 325.4 mmol h −1 g −1 of catalyst at 680 °C. The produced H−Ni/Al 2 O 3 contained metallic nickel, demonstrating an improved catalytic activity for CNT and hydrogen production from waste plastics.

Polyethylene terephthalate (PET) has been extensively used for the fabrication of various packaging materials, creating million tons of waste per year. Degrading and recycling PET waste has been identified as a prominent issue. Herein, we demonstrate an effective process to chemically convert PET to bis(2-hydroxyethyl) terephthalate (BHET) through the use of metal azolate framework-6 (MAF-6) as a catalyst in the presence of ethylene glycol. MAFs are a subclass of metal−organic frameworks (MOFs), with MAF-6 comprised of the metal ion Zn 2+ and the organic ligand 2-ethylimidazole. We have optimized the reaction temperature, reaction time, and catalyst amount to achieve up to a 92.4% conversion of PET and an 81.7% yield of BHET at 180 °C for 4 h. MAF-6 was easily recovered and reused for at least five times. We have also hypothesized a mechanism for the high conversion and yield of the PET glycolysis reaction catalyzed by MAF-6. The use of MAF-6 as a catalyst opens a new route for the postconsumer recycling of PET with remarkable practicality.

The waste plastic gasification in a fluidized bed for a continuous carbon nanotube (CNT) and hydrogen coproduction is a potential method for sustainable management. Ni/Al 2 O 3 catalysts have been synthesized by the impregnation method to upgrade hydrogen production and CNT synthesis. However, few studies investigated the effect of operating parameters for upcycling waste plastics into CNTs and hydrogen in the fluidized-bed system. The reaction temperature and the equivalence ratio (ER) were evaluated for CNT and hydrogen coproduction. Increasing the reaction temperature and lowering the ER enhanced the methane dry reforming, hydrocarbon dry reforming, and hydrocarbon direct decomposition for hydrogen and CNT coproduction. While increasing the reaction temperature from 500 to 700 °C can obtain higher CNT yield and H 2 production rate, the system heated to 700 °C and maintained at this temperature should provide more energy. Moreover, the gas composition at 600 °C with 0.1 ER contained more CH 4 and C 2 −C 5 hydrocarbons compared with that with a higher ER, which could be used as the carbon source of CNTs. The reaction temperature of the fluidized bed in the waste plastic gasification system controlled at 600 °C with 0.1 ER and the gasified products upgraded through a catalytic fixed-bed reactor at 680 °C exhibited an optimal catalytic performance of less-defective CNTs in 22.0% yield and H 2 production rate (385.1 mmol/h-g catalyst).

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Plastic waste is an emerging environmental issue for our society. Critical action to tackle this problem is to upcycle plastic waste as valuable feedstock. Thermochemical conversion of plastic waste has received growing attention. Although thermochemical conversion is promising for handling mixed plastic waste, it typically occurs at high temperatures (300–800 °C). Catalysts can play a critical role in improving the energy efficiency of thermochemical conversion, promoting targeted reactions, and improving product selectivity. This Review aims to summarize the state‐of‐the‐art of catalytic thermochemical conversions of various types of plastic waste. First, general trends and recent development of catalytic thermochemical conversions including pyrolysis, gasification, hydrothermal processes, and chemolysis of plastic waste into fuels, chemicals, and value‐added materials were reviewed. Second, the status quo for the commercial implementation of thermochemical conversion of plastic waste was summarized. Finally, the current challenges and future perspectives of catalytic thermochemical conversion of plastic waste including the design of sustainable and robust catalysts were discussed.

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