Self-Assembly of Metastable CoCu₂O₃ for Molecular Sensing and Catalysis

Metastable nanostructures are kinetically trapped in local energy minima featuring intriguing surface and material properties.¹ To build these advanced materials, there is a need for non-equilibrium processes capable of stabilizing a large range of crystal phases outside thermodynamic equilibrium conditions by closely and flexibly controlling atomic reactant composition, spatial temperature distribution and residence time. Here,² we demonstrate the capture of metastable pseudo-binary metal oxides at room temperature with scalable combustion-aerosol processes.³ By a combination of X-ray diffraction, electron microscopy and on-line flame characterization, we investigate the occurrence of metastable CoCu₂O₃ with controlled crystal size (4 – 16 nm) over thermodynamically stable CuO and Co₃O₄.⁴ We found that not only are precursor composition and flame temperatures key to successfully "freeze“ high-temperature phases at room temperature, but also the as-produced nanoparticles need to reside long enough at such high temperatures to effectively nucleate and develop the metastable crystalline phase. Immediate practical impact is demonstrated by exceptional sensing and catalytic performance for air pollutant detection (e.g., 15 parts-per-billion benzene). This is attributed to the acidic (Brønsted and Lewis) surface features,⁵ revealed by oxidation kinetics experiments and infrared spectroscopy of adsorbed pyridine.

References
[1] M, Aykol, S.S. Dwaraknath, W. Sun and K.A. Persson. Science Advances 2018, 4, eaaq0148.
[2] M. D’Andria, T. Elias Abi-Ramia Silva, E. Consogno, F. Krumeich and A.T. Güntner. arXiv:2406.10588
[3] A.T. Güntner, N.J. Pineau and S.E. Pratsinis. Progress in Energy and Combustion Science 2022, 90, 100992
[4] F. Driessens, G. Rieck and H. Coenen. Journal of Inorganic and Nuclear Chemistry 1968, 30, 747-753
[5] J. C. Védrine. Research on Chemical Intermediates 2015, 41, 9387-9423.