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Potassium hydride-intercalated graphite as an efficient heterogeneous catalyst for ammonia synthesis

Nature Catalysis volume 5, pages 222–230 (2022)Cite this article

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Abstract

Due to the high energy needed to break the N ≡ N bond (945 kJ mol−1), a key step in ammonia production is the activation of dinitrogen, which in industry requires the use of transition metal catalysts such as iron (Fe) or ruthenium (Ru), in combination with high temperatures and pressures. Here we demonstrate a transition-metal-free catalyst—potassium hydride-intercalated graphite (KH0.19C24)—that can activate dinitrogen at very moderate temperatures and pressures. The catalyst catalyses NH3 synthesis at atmospheric pressure and achieves NH3 productivity (µmolNH3 gcat−1 h−1) comparable to the classical noble metal catalyst Ru/MgO at temperatures of 250–400 °C and 1 MPa. Both experimental and computational calculation results demonstrate that nanoconfinement of potassium hydride between the graphene layers is crucial for the activation and conversion of dinitrogen. Hydride in the catalyst participates in the hydrogenation step to form NH3. This work shows the promise of light metal hydride materials in the catalysis of ammonia synthesis.

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Fig. 1: Schematic illustration of the preparation process of the KH0.19C24 catalyst and XRD patterns.
Fig. 2: NH3 synthesis catalysed by KH0.19C24.
Fig. 3: Electron microscopy analyses of the KH0.19C24 catalyst after ammonia synthesis.
Fig. 4: Characterization of the N2-treated KH0.19C24 catalyst.
Fig. 5: Kinetic analyses of ammonia synthesis on the KH0.19C24 catalyst.
Fig. 6: DFT calculations for potential ammonia synthesis mechanisms on KH-intercalated graphite.

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Data availability

The data supporting the findings of this study are available within the article and the Supplementary Information. Atomic coordinates of the optimized computational models are supplied as Supplementary Data 1. All raw data are available on reasonable request by contacting the corresponding authors. Source data are provided with this paper.

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Acknowledgements

We thank S. Zanoni for N2 physisorption measurements, and Netherlands Organisation for Scientific Research (NWO)-Vici (no. 16.130.344) for overall funding of the project. P.N. and P.E.d.J. acknowledge support from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (ERC-2014-CoG, no. 648991). S.E. acknowledges funding from the initiative ‘Computational Sciences for Energy Research’ from Shell and NWO grant no. 15CSTT05. The computational part of this work was sponsored by NWO Exact and Natural Sciences for the use of supercomputer facilities. We thank P. Chen and J. Guo for useful discussions.

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Author notes

  1. Jan P. Hofmann

    Present address: Surface Science Laboratory, Department of Materials and Earth Sciences, Technical University of Darmstadt, Darmstadt, Germany

Authors and Affiliations

  1. Materials Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, the Netherlands

    Fei Chang, Jan Willem de Rijk, Johannes D. Meeldijk, Peter Ngene & Petra E. de Jongh

  2. Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands

    Ilker Tezsevin & Süleyman Er

  3. Electron Microscopy Center, Utrecht University, Utrecht, the Netherlands

    Johannes D. Meeldijk

  4. Laboratory for Inorganic Materials and Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, the Netherlands

    Jan P. Hofmann

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Contributions

P.E.d.J. and P.N. conceived and supervised the research. F.C. designed and performed experiments and data analysis. I.T. and S.E. performed DFT calculations and results analysis. J.W.d.R. constructed the set-up for catalytic activity tests. J.P.H. performed XPS analysis. J.D.M. was responsible for electron microscopy measurements. F.C., P.N. and P.E.d.J. wrote the paper, with I.T. and S.E. contributing the section on DFT calculations. All authors commented on the manuscript.

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Correspondence to Peter Ngene or Petra E. de Jongh.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–28, Tables 1–6 and references.

Supplementary Data 1

Atomic coordinates of the optimized computational models.

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Statistical source data.

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Statistical source data.

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Statistical source data.

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Chang, F., Tezsevin, I., de Rijk, J.W. et al. Potassium hydride-intercalated graphite as an efficient heterogeneous catalyst for ammonia synthesis. Nat Catal 5, 222–230 (2022). https://doi.org/10.1038/s41929-022-00754-x

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