The use of Ni-Fe catalysts for the catalytic pyrolysis of real-world waste plastics to produce hydrogen and high value carbon nanotubes (CNT), and the influence of catalyst composition and support materials has been investigated. Experiments were conducted in a two stage fixed bed reactor, where plastics were pyrolysed in the first stage followed by reaction of the evolved volatiles over the catalyst in the second stage. Different catalyst temperatures (700, 800, 900 °C) and steam to plastic ratios (0, 0.3, 1, 2.6) were explored to optimize the product hydrogen and the yield of carbon nanotubes deposited on the catalyst. The results showed that the growth of carbon nanotubes and hydrogen were highly dependent on the catalyst type and the operational parameters. Fe/γ-Al2O3 produced the highest hydrogen yield (22.9 mmol H2/gplastic) and carbon nanotubes yield (195 mg g−1plastic) among the monometallic catalysts, followed by Fe/α-Al2O3, Ni/γ-Al2O3 and Ni/α-Al2O3. The bimetallic Ni-Fe catalyst showed higher catalytic activity in relation to H2 yield than the monometallic Ni or Fe catalysts because of the optimum interaction between metal and support. Further investigation of the influence of steam input and catalyst temperature on product yields found that the optimum simultaneous production of CNTs (287 mg g−1plastic) and hydrogen production (31.8 mmol H2/gplastic) were obtained at 800 °C in the absence of steam and in the presence of the bimetallic Ni-Fe/γ-Al2O3 catalyst.

Co-production of hydrogen and carbon nanotubes from real-world waste plastics: Influence of catalyst composition and operational parameters

Recent progress in controlled carbonization of (waste) polymers

Improving flame retardancy of IFR/PP composites through the synergistic effect of organic montmorillonite intercalation cobalt hydroxides modified by acidified chitosan

Carbon nanotubes were produced from post-consumer mixed waste plastics using a pyrolysis-catalysis process. The catalysts used were Ni-Fe bimetals supported over four different porous materials. The Ni-Fe/MCM41 catalyst displayed the highest catalytic activity for the pyrolysis-catalysis of the waste plastics in terms of carbon material yield at 55.60 wt.%. The order of catalytic activity was Ni-Fe/MCM41> Ni-Fe/ZSM5> Ni-Fe/Beta > Ni-Fe/NKF5, which was closely related to their differences in catalyst pore volume and catalyst reducibility. Formation of Ni-Fe alloy with fine particle dispersion over the Ni-Fe/MCM41 catalyst is suggested to be crucial for the promotion of the decomposition of the carbon precursors and subsequent precipitation to form carbon nanotubes. Whereas, the large catalyst particle size for the Ni-Fe/Beta catalyst led to irregular carbon shapes with a simultaneous decrease in purity and graphitization of the nanotubes. By-product production of hydrogen in large quantities (38.10 mmol H2  g−1plastic) could be used as process fuel.

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Carbon nanotubes from post-consumer waste plastics: Investigations into catalyst metal and support material characteristics

The massive generation of plastic wastes without satisfactory treatment has induced severe environmental problems and gained increasing attentions. In this Minireview, recent progresses in the chemical upcycling of plastic wastes by using various methods (mainly in the past three to five years) is summarized. The chemical upcycling of plastic wastes points out a "plastic-based refinery" concept, which is to use the plastic wastes as platform feedstocks to produce highly valuable monomeric or oligomeric compounds, putting the plastic wastes back into a circular economy. The different chemical methods to upcycle plastic wastes, including hydrogenolysis, photocatalysis, pyrolysis, solvolysis, and others, are introduced in each section to valorize diverse plastic feedstocks into value-added chemicals, materials, or fuels. In addition, other emerging technologies as well as the new generation of plastic thermosets are covered.

Recent Progress in the Chemical Upcycling of Plastic Wastes.

This study designed a novel Ni–Al bimetallic catalyst for preparation of multiwalled carbon nanotubes (MWCNTs) from polypropylene (PP). The study further investigated the influence of Al content on the catalytic activity of Ni catalyst. A series of bimetallic Ni–Al catalysts were prepared and then characterized by X-ray diffraction, N2-adsorption–desorption isotherms, transmission electron microcopy and temperature programmed reduction analysis. It was found that bimetallic Ni–Al catalysts had higher surface area, higher reduction temperature, smaller Ni particle size and improved stability. Consequently, the addition of Al not only dramatically enhanced the yield of MWCNTs, but simultaneously improved the morphology and graphitization of MWCNTs. The activities of the bimetallic Ni–Al catalysts were dependent on their composition. Among the different Ni–Albimetallic catalysts, Ni–Al catalyst showed the highest activity when the ratio of Ni/Al was 9/1. Moreover, the obtained MWCNTs presented smooth surface with highest graphitization degree. The improvement of catalytic activity and stability obtained for bimetallic Ni–Al catalysts was attributed to an appropriate interaction and synergy between Ni species and amorphous Al2O3. The combined results indicate that the addition of Al to Ni catalyst with an appropriate amount of Al can give rise to a bimetallic catalyst with excellent properties for synthesis of MWCNTs from PP. With our bimetallic Ni–Al catalyst, it is promising to achieve mass production of MWCNTs by using waste polymers as feedstock.

Ni–Al bimetallic catalysts for preparation of multiwalled carbon nanotubes from polypropylene: Influence of the ratio of Ni/Al

Synergistic effect of Ni-based bimetallic catalyst with intumescent flame retardant on flame retardancy and thermal stability of polypropylene

NiO catalyst supported on Fe-pillared montmorillonite (5–15 wt% Ni) was prepared via a simple conventional impregnation method. The physicochemical properties of the Ni catalyst were characterised by X-ray diffraction, inductively coupled plasma-atomic emission spectrometry and transmission electron microscopy. The Ni catalyst, together with organic montmorillonite (OMMT), was employed to prepare multi-walled carbon nanotubes (MWCNTs) by using polypropylene (PP) as a precursor. An increase in Ni loading of the catalyst led to a significant increase in the yield of MWCNTs at the expense of a slight decline in quality of the obtained MWCNTs. Moreover, OMMT altered the degradation process of PP, which resulted in a much higher fraction of light hydrocarbons in degradation products. As such, a substantial increase in the yield of MWCNTs was attained. In addition, the obtained MWCNTs were used as flame retardant for PP, and significantly enhanced thermal stability and flame retardancy according to thermogravimetry analysis and cone data, respectively. PP/MWCNTs nanocomposite exhibited higher degradation temperature, longer ignition time, much lower heat release rate and smoke production rate. This work offers an efficient Ni catalyst to convert PP into MWCNTs which could be applied as flame retardant for polymers.

Preparation of multi-walled carbon nanotubes and its application as flame retardant for polypropylene

This study designs Ni–Mg bimetallic catalysts for preparation of multi-walled carbon nanotubes (MWCNTs) from polypropylene (PP). The study further investigates the influence of Mg content on the catalytic activity of Ni catalyst. It is found that bimetallic Ni–Mg catalysts have higher reduction temperature, smaller Ni particle size and improved stability. Consequently, the addition of Mg not only enhances the yield of MWCNTs, but simultaneously improves the morphology and graphitization of MWCNTs. The activities of the bimetallic Ni–Mg catalysts are dependent on their composition. Among the different Ni–Mg bimetallic catalysts ration, Ni–Mg catalyst shows the highest activity when the ratio of Ni/Mg is 9/1. Moreover, the obtained MWCNTs presents smooth surface with highest graphitization degree. With our bimetallic Ni–Al catalyst, it is promising to achieve mass production of MWCNTs by using waste polymers as feedstock.

Yinlong Shen

Papers

Ni–Al bimetallic catalysts for preparation of multiwalled carbon nanotubes from polypropylene: Influence of the ratio of Ni/Al

Synergistic effect of Ni-based bimetallic catalyst with intumescent flame retardant on flame retardancy and thermal stability of polypropylene

Preparation of multi-walled carbon nanotubes and its application as flame retardant for polypropylene

Ni-Mg Bimetallic Catalysts for Preparation of Multi-Walled Carbon Nanotubes from Polypropylene: Influence of the Ratio of Ni/Mg

Preparation of core-shell Ag3PO4@GOQDs and degradation of ciprofloxacin under visible light