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The role of surface hydroxyls in the entropy-driven adsorption and spillover of H2 on Au/TiO2 catalysts

Nature Catalysis volume 6, pages 710–719 (2023)Cite this article

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Abstract

Hydrogen spillover involves the migration of H atom equivalents from metal nanoparticles to a support. While well documented, H spillover is poorly understood and largely unquantified. Here we measure weak, reversible H2 adsorption on Au/TiO2 catalysts, and extract the surface concentration of spilled-over hydrogen. The spillover species (H*) is best described as a loosely coupled proton/electron pair distributed across the titania surface hydroxyls. In stark contrast to traditional gas adsorption systems, H* adsorption increases with temperature. This unexpected adsorption behaviour has two origins. First, entropically favourable adsorption results from high proton mobility and configurational surface entropy. Second, the number of spillover sites increases with temperature, due to increasing hydroxyl acid–base equilibrium constants. Increased H* adsorption correlates with the associated changes in titania surface zwitterion concentration. This study provides a quantitative assessment of how hydroxyl surface chemistry impacts spillover thermodynamics, and contributes to the general understanding of spillover phenomena.

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Fig. 1: Temperature and particle size effects on H2 adsorption.
Fig. 2: Au loading effects on H2 adsorption and spillover.
Fig. 3: Schematic showing H2 adsorption at the MSI.
Fig. 4: H* adsorption thermodynamics.
Fig. 5: Entropy diagram for H* adsorption at 25 °C.
Fig. 6: Entropic contributions to hydrogen spillover energetics.
Fig. 7: DFT model for H* adsorbed on rutile (110) and anatase (001).
Fig. 8: Temperature dependence of TiO2 surface hydroxyl chemistry.

Data availability

Raw data are available through ScholarSphere, Penn State’s open access repository at https://scholarsphere.psu.edu/ or available from the authors upon reasonable request. The atomic coordinates of the models in DFT calculations of charge density difference and spin density are provided in Supplementary Data 1.

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Acknowledgements

The authors gratefully acknowledge the Department of Energy Basic Energy Sciences Program (DE-SC0022053 and DE-SC0016192) for primary support of this work. Preliminary experiments were supported by the National Science Foundation (CBET-1803769, 1803808 and 2102430) and the Research Corporation for Science Advancement. The computational work was completed with resources provided by the Research Computing Data Core at the University of Houston. We thank M. Janik at Penn State for invaluable discussions and T. Xie for his assistance in collecting TEM data.

Author information

Author notes

  1. K. B. Sravan Kumar

    Present address: Umicore AG & Co. KG, Hanau, Germany

  2. These authors contributed equally: Akbar Mahdavi-Shakib, Todd N. Whittaker.

Authors and Affiliations

  1. Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, USA

    Akbar Mahdavi-Shakib, Tae Yong Yun, Robert M. Rioux & Bert D. Chandler

  2. Department of Chemistry, Trinity University, San Antonio, TX, USA

    Todd N. Whittaker & Lauren C. Rich

  3. Department of Chemical and Biological Engineering, The University of Colorado, Boulder, CO, USA

    Todd N. Whittaker

  4. Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX, USA

    K. B. Sravan Kumar, Shengguang Wang & Lars C. Grabow

  5. Department of Chemistry, The Pennsylvania State University, University Park, PA, USA

    Robert M. Rioux & Bert D. Chandler

  6. Texas Center for Superconductivity at the University of Houston (TcSUH), University of Houston, Houston, TX, USA

    Lars C. Grabow

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Contributions

Conceptualization: B.D.C., T.N.W. and A.M.-S. Formal analysis: A.M.-S., T.N.W., T.Y.Y., S.W., K.B.S.K. and L.C.R. Funding acquisition: B.D.C., L.C.G. and R.M.R. Investigation: A.M.-S., T.N.W., T.Y.Y., L.C.R., S.W. and K.B.S.K. Methodology: A.M.-S., T.N.W., T.Y.Y. and S.G. Project administration: B.D.C. Supervision: B.D.C., A.M.-S. and L.C.G. Visualization: A.M.-S., T.N.W., T.Y.Y. and S.W. Writing—original draft: B.D.C. and A.M.-S. Writing—review and editing: T.N.W., R.M.R., L.C.G., S.W. and K.B.S.K.

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Correspondence to Bert D. Chandler.

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Nature Catalysis thanks Charles Campbell, Shuai Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Methods, Discussion, Figs. 1–19, Tables 1–7 and References.

Supplementary Data 1

This document contains the atomic coordinates of the models in DFT calculations of charge density difference and spin density.

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Mahdavi-Shakib, A., Whittaker, T.N., Yun, T.Y. et al. The role of surface hydroxyls in the entropy-driven adsorption and spillover of H2 on Au/TiO2 catalysts. Nat Catal 6, 710–719 (2023). https://doi.org/10.1038/s41929-023-00996-3

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