Abstract
Solvent structures that surround active sites reorganize during catalysis and influence the stability of surface intermediates. Within zeolite pores, H2O molecules form hydrogen-bonded structures that differ substantially from bulk H2O. Here, we show by spectroscopic measurements and molecular dynamics simulations that H2O molecules form bulk-like three-dimensional structures within 1.3 nm cages, whereas H2O molecules coalesce into oligomeric one-dimensional chains when the pore diameter falls below 0.65 nm. The differences between these solvent structure motifs provide opportunities to manipulate enthalpy–entropy compensation relationships and greatly increase the rates of catalysis. We describe how the reorganization of these pore-size-dependent H2O structures during alkene epoxidation catalysis gives rise to entropy gains that increase the turnover rates by up to 400-fold. Collectively, this work shows that solvent molecules form distinct structures with a highly correlated motion within microporous environments, and the reorganization of these structures may be controlled to confer stability to the desired reactive intermediates.

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Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author upon reasonable request. MD trajectories of the last 100 nanoseconds of equilibration, ab initio MD trajectories and initial and final simulated zeolite structures are available on Zenodo at https://doi.org/10.5281/zenodo.5079480. Source data are provided with this paper.
Code availability
The code and algorithms for analysing the MD simulations are deposited on Zenodo at https://doi.org/10.5281/zenodo.5079480.
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Acknowledgements
This work was supported by the Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DE-SC0020224 (D.T.B., J.Z.T., E.Z.A. and D.W.F.). D.T.B. was also partially supported by the Department of Defense through the National Defense Science & Engineering Graduate (NDSEG) Fellowship Program and through a Dissertation Completion Fellowship from the University of Illinois. E.Z.A. was partially supported by the US Army Research Office (W911NF-18-1-0100). C.P.N. was supported by Honeywell UOP. This work was carried out, in part, in the Frederick Seitz Materials Research Laboratory. M.C.C. and D.S. acknowledge support from Blue Waters sustained-petascale computing project, which is supported by the National Science Foundation (awards OCI-0725070 and ACI-1238993), the State of Illinois and, as of December 2019, the National Geospatial-Intelligence Agency. Blue Waters is a joint effort of the University of Illinois at Urbana-Champaign and its National Center for Supercomputing Applications.
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D.T.B. and D.W.F. conceptualized the paper. D.T.B., J.Z.T., E.Z.A. and C.P.N. synthesized and characterized the zeolites. D.T.B. and J.Z.T. performed the spectroscopic and kinetic measurements. M.C.C. and D.S. performed the MD simulations. D.T.B. wrote the original draft of the manuscript and all the authors reviewed and edited its content. D.S. and D.W.F. supervised the work.
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Supplementary Figs. 1–18, Notes 1–14, Tables 1–9 and references.
Supplementary Video 1
Representative dynamics of water molecules within Ti-FAU-F from the final 25 ns of the classical MD simulation.
Supplementary Video 2
Representative dynamics of water molecules within Ti-FAU-OH from the final 25 ns of the classical MD simulation.
Supplementary Video 3
Representative dynamics of water molecules within Ti-BEA-F from the final 25 ns of the classical MD simulation.
Supplementary Video 4
Representative dynamics of water molecules within Ti-BEA-OH from the final 25 ns of the classical MD simulation.
Supplementary Video 5
Representative dynamics of water molecules within Ti-MFI-F from the final 25 ns of the classical MD simulation.
Supplementary Video 6
Representative dynamics of water molecules within Ti-MFI-OH from the final 25 ns of the classical MD simulation.
Supplementary Video 7
Representative dynamics of water molecules within Si-CDO-F from the final 25 ns of the classical MD simulation.
Supplementary Video 8
Representative dynamics of water molecules within Si-CDO-OH from the final 25 ns of the classical MD simulation.
Source data
Source Data Fig. 1
Statistical Source Data.
Source Data Fig. 2
Statistical Source Data.
Source Data Fig. 3
Statistical Source Data.
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Bregante, D.T., Chan, M.C., Tan, J.Z. et al. The shape of water in zeolites and its impact on epoxidation catalysis. Nat Catal 4, 797–808 (2021). https://doi.org/10.1038/s41929-021-00672-4
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DOI: https://doi.org/10.1038/s41929-021-00672-4