Metal oxide alloys (for example AxByOz) exhibit dramatically different catalytic properties in response to small changes in composition (the A:B ratio). Here, we show that for the ternary zinc–chromium oxide (ZnCrO) catalysts the activity and selectivity during syngas (CO/H2) conversion strongly depend on the Zn:Cr ratio. By using a global neural network potential, stochastic surface walking global optimization and first principles validation, we constructed a thermodynamics phase diagram for Zn–Cr–O that reveals the presence of a small stable composition island, that is, Zn:Cr:O = 6:6:16 to 3:8:16, where the oxide alloy crystallizes into a spinel phase. By changing the Zn:Cr ratio from 1:2 to 1:1, the ability to form oxygen vacancies increases appreciably and extends from the surface to the subsurface, in agreement with previous experiments. This leads to the critical presence of a four-coordinated planar Cr2+ cation that markedly affects the syngas conversion activity and selectivity to methanol, as further proved by microkinetics simulations.
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The software code for LASP and the NN potentials used within the article are available from the corresponding author upon request or on the website http://www.lasphub.com.
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This work was supported by the National Key Research and Development Program of China (2018YFA0208600) and the National Science Foundation of China (21573149, 21533001 and 91745201).
The authors declare no competing interests.
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Ma, S., Huang, SD. & Liu, ZP. Dynamic coordination of cations and catalytic selectivity on zinc–chromium oxide alloys during syngas conversion. Nat Catal 2, 671–677 (2019). https://doi.org/10.1038/s41929-019-0293-8
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