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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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.
The authors declare no competing interests.
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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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