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Efficient solvent- and hydrogen-free upcycling of high-density polyethylene into separable cyclic hydrocarbons

Nature Nanotechnology volume 18, pages 772–779 (2023)Cite this article

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Abstract

Plastic pollution is a planetary threat that has been exacerbated by the COVID-19 pandemic due to the surge in medical waste, personal protective equipment and takeaway packaging. A socially sustainable and economically viable method for plastic recycling should not use consumable materials such as co-reactants or solvents. Here we report that Ru nanoparticles on zeolitic HZSM-5 catalyse the solvent- and hydrogen-free upcycling of high-density polyethylene into a separable distribution of linear (C1 to C6) and cyclic (C7 to C15) hydrocarbons. The valuable monocyclic hydrocarbons accounted for 60.3 mol% of the total yield. Based on mechanistic studies, the dehydrogenation of polymer chains to form C=C bonds occurs on both Ru sites and acid sites in HZSM-5, whereas carbenium ions are generated on the acid sites via the protonation of the C=C bonds. Accordingly, optimizing the Ru and acid sites promoted the cyclization process, which requires the simultaneous existence of a C=C bond and a carbenium ion on a molecular chain at an appropriate distance, providing high activity and cyclic hydrocarbon selectivity.

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Fig. 1: Catalytic performance of Ru/HZSM-5(300) in the upcycling of HDPE.
Fig. 2: Reaction route for HDPE upcycling over Ru/HZSM-5(300).
Fig. 3: The role of Ru in the upcycling of HDPE over Ru/HZSM-5(300).
Fig. 4: The role of zeolites in the upcycling of HDPE.
Fig. 5: Evaluation of the robustness of Ru/HZSM-5(300) in PE upcycling.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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Acknowledgements

This work was supported by the National Key Research and Development Program of China (2021YFA1500500 and 2019YFA0405600), the CAS Project for Young Scientists in Basic Research (YSBR-051), the National Science Fund for Distinguished Young Scholars (21925204), the NSFC (U19A2015, 22221003 and 22204158), the Fundamental Research Funds for the Central Universities, the Provincial Key Research and Development Program of Anhui (202004a05020074), K. C. Wong Education (GJTD-2020-15), the DNL Cooperation Fund, CAS (DNL202003), the Natural Science Foundation of Anhui Province (2208085QB42) and the USTC Research Funds of the Double First-Class Initiative. This work was partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication.

Author information

Author notes

  1. These authors contributed equally: Junjie Du, Lin Zeng.

Authors and Affiliations

  1. Hefei National Research Center for Physical Sciences at the Microscale, Key Laboratory of Strongly Coupled Quantum Matter Physics of Chinese Academy of Sciences, Key Laboratory of Surface and Interface Chemistry and Energy Catalysis of Anhui Higher Education Institutes, Department of Chemical Physics, University of Science and Technology of China, Hefei, People’s Republic of China

    Junjie Du, Lin Zeng, Tao Yan, Chuanhao Wang, Menglin Wang, Lei Luo, Wenlong Wu, Zijun Peng, Hongliang Li & Jie Zeng

  2. School of Chemistry and Chemical Engineering, Anhui University of Technology, Ma’anshan, People’s Republic of China

    Jie Zeng

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Contributions

J.D., L.Z., H.L. and J.Z. designed the study and wrote the paper. J.D., T.Y. and C.W. synthesized the catalysts. J.D., L.Z., M.W., L.L., W.W. and H.L. performed the catalytic tests. L.Z. and Z.P. conducted the PXRD measurements. W.W., H.L., Z.P. and J.Z. conducted the mechanistic measurements, including TPD and SVUV-PIMS. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Jie Zeng.

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Extended data

Extended Data Fig. 1 Structure characterization and catalytic performance of Ru/HZSM-5(300).

(a) XRD pattern of Ru/HZSM-5(300). (b) TEM images of fresh Ru/HZSM-5(300). (c) TEM images of Ru/HZSM-5(300) after HDPE upcycling at 280 °C for 24 h. (d) Detailed hydrocarbon distribution of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics over Ru/HZSM-5(300) in HDPE upcycling at 280 °C for 24 h. (e) Full-range GC-MS analysis of products over Ru/HZSM-5(300) in HDPE upcycling at 280 °C for 24 h.

Source data

Extended Data Fig. 2 The influence of external H2.

(a) Yields of volatiles/gases, liquid phase products, and insoluble hydrocarbons. (b) Selectivity among volatiles/gases and liquid phase products over Ru/HZSM-5(300) in HDPE upcycling at 280 °C for 24 h with 2.5 MPa external H2 or without H2. (c,d) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics over Ru/HZSM-5(300)-with external H2 in HDPE upcycling at 280 °C for 24 h. (e) Full-range GC-MS analysis of products over Ru/HZSM-5(300)-with external H2 in HDPE upcycling at 280 °C for 24 h.

Source data

Extended Data Fig. 3 Structure characterization of HZSM-5(300)_R.

(a) XRD pattern of HZSM-5(300)_R. (b) Normalized Al 2p XPS peak intensity on the surface of HZSM-5(300) and HZSM-5(300)_R.

Source data

Extended Data Fig. 4 The role of surface acid sites.

(a) Yields of volatiles/gases, liquid phase products, and insoluble hydrocarbons. (b) Selectivity among volatiles/gases and liquid phase products over HZSM-5(300) and HZSM-5(300)_R in HDPE upcycling at 280 °C for 24 h. (c,d) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics over Ru/HZSM-5(300)_R in HDPE upcycling at 280 °C for 24 h. (e) Full-range GC-MS analysis of products over Ru/HZSM-5(300)_R in HDPE upcycling at 280 °C for 24 h.

Source data

Extended Data Fig. 5 Detailed product distribution over Ru/USY in HDPE upcycling at 280 °C for 24 h.

(a,b) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics. (c) Full-range GC-MS analysis of products.

Source data

Extended Data Fig. 6 The influence of pore structures.

(a,b) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics over Ru/SAPO-34 in HDPE upcycling at 280 °C for 24 h. (c) Full-range GC-MS analysis of products over Ru/SAPO-34 in HDPE upcycling at 280 °C for 24 h. (d) Schematic illustration of pore confinement in SAPO-34. SAPO-34 cages have large empty interiors and narrow mouths. Once the fused aromatic rings are generated, they cannot exit the narrow mouth, resulting in the accumulation within the cage to form cokes.

Source data

Extended Data Fig. 7 Catalytic performance of Ru/HZSM-5(300)-Spent in HDPE upcycling at 280 °C for 24 h.

(a) Yields of volatiles/gases, liquid phase products, and insoluble hydrocarbons. (b) Selectivity among volatiles/gases and liquid phase products over fresh and spent Ru/HZSM-5(300) in HDPE upcycling at 280 °C for 24 h. (c,d) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics over Ru/HZSM-5(300)-Spent in HDPE upcycling at 280 °C for 24 h. (e) Full-range GC-MS analysis of products over Ru/HZSM-5(300)-Spent in HDPE upcycling at 280 °C for 24 h.

Source data

Extended Data Fig. 8 Detailed product distribution over Ru/HZSM-5(300) in three consecutive runs of HDPE upcycling at 280 °C for 24 h.

(a,b,d,e) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics. (c,f) Full-range GC-MS analysis of products. Panels a-c refer to the second run. Panels d-f refer to the third run.

Source data

Extended Data Fig. 9 Detailed product distribution over Ru/HZSM-5(300) in LDPE upcycling at 280 °C for 24 h.

(a,b) Detailed hydrocarbon selectivity of alkanes, olefins, cycloalkanes, cycloolefins, and aromatics. (c) Full-range GC-MS analysis of products.

Source data

Supplementary information

Supplementary Information

Supplementary Notes 1 and 2, Figs. 1–26 and Tables 1–16.

Supplementary Data 1

Source data for supplementary figures.

Source data

Source Data Fig. 1

Source data for the catalytic performance of Ru/HZSM-5(300) in the upcycling of HDPE.

Source Data Fig. 3

Source data for the role of Ru in the upcycling of HDPE over Ru/HZSM-5(300).

Source Data Fig. 4

Source data for the role of zeolites in the upcycling of HDPE.

Source Data Fig. 5

Source data for the robustness evaluation of Ru/HZSM-5(300) in PE upcycling.

Source Data Extended Data Fig. 1

Source data for the structure characterization and catalytic performance of Ru/HZSM-5(300).

Source Data Extended Data Fig. 2

Source data for the influence of external H2 in the upcycling of HDPE over Ru/HZSM-5(300).

Source Data Extended Data Fig. 3

Source data for the structure characterization of HZSM-5(300)_R.

Source Data Extended Data Fig. 4

Source data for the role of surface acid in the upcycling of HDPE over HZSM-5(300).

Source Data Extended Data Fig. 5

Source data for the detailed product distribution over Ru/USY in the upcycling of HDPE at 280 °C for 24 h.

Source Data Extended Data Fig. 6

Source data for the influence of the pore structure of SAPO-34 in HDPE upcycling.

Source Data Extended Data Fig. 7

Source data for the catalytic performance of Ru/HZSM-5(300)-Spent in the upcycling of HDPE at 280 °C for 24 h.

Source Data Extended Data Fig. 8

Source data for the detailed product distribution over Ru/HZSM-5(300) in three consecutive runs of HDPE upcycling at 28 C for 24 h.

Source Data Extended Data Fig. 9

Source data for the detailed product distribution over Ru/HZSM-5(300) in LDPE upcycling at 28 °C for 24 h.

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Du, J., Zeng, L., Yan, T. et al. Efficient solvent- and hydrogen-free upcycling of high-density polyethylene into separable cyclic hydrocarbons. Nat. Nanotechnol. 18, 772–779 (2023). https://doi.org/10.1038/s41565-023-01429-9

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