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Operando NAP-XPS unveils differences in MoO3 and Mo2C during hydrodeoxygenation

Abstract

MoO3 and Mo2C have emerged as remarkable catalysts for the selective hydrodeoxygenation (HDO) of a wide range of oxygenates at low temperatures (that is, ≤673 K) and H2 pressures (that is, ≤1 bar). Although both catalysts can selectively cleave C–O bonds, the nature of their active sites remains unclear. Here we used operando near-ambient pressure X-ray photoelectron spectroscopy to reveal important differences in the Mo 3d oxidation states between the two catalysts during the hydrodeoxygenation of anisole. This technique revealed that, although both catalysts featured a surface oxycarbidic phase, the oxygen content and the underlying phase of the material impacted the reactivity and product selectivity during the hydrodeoxygenation. MoO3 transitioned between 5+ and 6+ oxidation states during the operation, consistent with an oxygen-vacancy driven mechanism wherein the oxygenate is activated at undercoordinated Mo sites. In contrast, Mo2C showed negligible oxidation state changes during hydrodeoxygenation and maintained mostly 2+ states throughout the reaction.

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Fig. 1: NAP-XPS of prereduced MoO3 during the HDO of anisole at a photon energy of 473 eV.
Fig. 2: NAP-XPS of Mo2C during the HDO of anisole at a photon energy of 473 eV.
Fig. 3: Normalized Mo 3d spectra of Mo2C-pass during the HDO of anisole measured at a photon energy of 473 eV.

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All data are available from the corresponding author upon reasonable request.

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Acknowledgements

This research was funded by BP through the MIT Energy Initiative Advanced Conversion Research Program and the National Science Foundation (award no. 1454299). We thank Helmholtz-Zentrum Berlin for the allocation of synchrotron radiation beam time at the ISISS beamline of BESSY II. T.E.J. acknowledges the Alexander-von-Humboldt Foundation for financial support.

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K.M. and Y.R.-L. conceived the research ideas and designed the experiments. K.M. prepared the materials and performed the PXRD. K.M., E.M.A., D.T. and K.S. performed the NAP-XPS experiments. K.M. and D.T. analysed the XPS data. T.E.J. performed the DFT calculations. K.M. and Y.R.-L. co-wrote the paper. Y.R.-L. supervised the project. All the authors discussed the results and commented on the different versions of the manuscript.

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Correspondence to Yuriy Román-Leshkov.

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Supplementary Methods; Supplementary Figures 1–58; Supplementary Tables 1-11; Supplementary References

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Murugappan, K., Anderson, E.M., Teschner, D. et al. Operando NAP-XPS unveils differences in MoO3 and Mo2C during hydrodeoxygenation. Nat Catal 1, 960–967 (2018). https://doi.org/10.1038/s41929-018-0171-9

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