Crossing the great divide between single-crystal reactivity and actual catalyst selectivity with pressure transients

Abstract

The quantitative prediction of catalyst selectivity is essential to the design of efficient catalytic processes and requires a detailed knowledge of the reaction mechanism and rate constants. Here we present a study that accurately predicts, using the kinetics and a mechanism derived from fundamental studies on single-crystal gold, the product distribution resulting from the complex reaction network that governs the oxidative coupling of methanol, catalysed by nanoporous gold between 360 and 425 K and for a vast range of pressures. Analysis of the transient product responses to micropulses of methanol over nanoporous gold yields a precise understanding of the marked dependence of selectivity on pressure, surface oxygen coverage and temperature. The key to a high selectivity for methyl formate is the surface lifetime and abundance of the methoxy. This successful microkinetic modelling of catalytic reactions across a wide set of reaction conditions is broadly applicable to predicting catalytic selectivity and provides a pathway to designing more efficient catalytic processes.

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Fig. 1: Elementary reaction steps and competing pathways for the oxidation of methanol on Au(111).
Fig. 2: The temperature-programmed reaction product spectrum of methanol reacting with preadsorbed O on Au(111).
Fig. 3: Summary of the reaction network in Fig. 1 for methanol self-coupling over a NPAu catalyst.
Fig. 4: Gas composition at the reactor exit that result from pulsed methanol exposure to nanoporous Ag0.03Au0.97.
Fig. 5: Height-normalized transient responses.
Fig. 6: Computed product selectivity contours for methanol coupling over nanoporous Ag0.03Au0.97.
Fig. 7: The effect of surface methoxy concentration on the coupling selectivity.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award no. DE-SC0012573. E.A.R. expresses his gratitude to U. Olsbye for her support and enthusiasm about applying TAP for mechanistic research in catalysis. E.A.R. acknowledges the Norwegian Research Council for financial support through contract 239193.

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R.J.M. and E.A.R. guided the research. C.R. and S.K. performed the experiments. C.R. performed the microkinetic modelling. R.J.M., C.R, E.A.R., S.K. and C.M.F. all participated in frequent discussions and contributed significantly to writing the manuscript.

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Correspondence to Robert. J. Madix.

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Supplementary Notes 1–8, Supplementary Figures 1–5, Supplementary Tables 1–4 and Supplementary References

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Reece, C., Redekop, E.A., Karakalos, S. et al. Crossing the great divide between single-crystal reactivity and actual catalyst selectivity with pressure transients. Nat Catal 1, 852–859 (2018). https://doi.org/10.1038/s41929-018-0167-5

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