Doping of metal oxides has been studied for enhancing activity towards, e.g. oxidation reactions or to induce visible light absorption in photocatalysts. First principles density functional theory (DFT) simulations of doped oxides have been important in understanding how the doping process can change (1) the electronic structure and metal oxidation states of the host and the dopant cations and (2) the reactivity, which is measured by the oxygen vacancy formation energy. There are ample DFT studies of doped reducible oxides such as TiO2 and CeO2 which have identified host and dopant cation oxidation states and have shown which dopants are suitable for reducing the cost to form oxygen vacancies. Cr2O3 is a reducible oxide but there is little published work on the doping of chromia. In this contribution we present extensive DFT simulations, with a +U correction on Cr to describe the localised 3d states in Cr, of bulk Cr2O3 doped with a series of metal cations. Our results allow us to identify the oxidation states of Cr and the dopant after incorporation and we generally find that Cr maintains its 3+ oxidation state. For oxygen vacancy, formation we find that all dopants considered lower the oxygen vacancy formation energy, from 5.26 eV, with Ce leading to spontaneous O vacancy formation, attributed in part to the large ionic radius of Ce. La and Al substantially reduce the cost of forming oxygen vacancies, while divalent dopants also give a reduction of 2 -3 eV in the formation energy. We are thus able to identify dopants in Cr2O3 that can enhance its reactivity and identify the mechanism behind this enhanced activity. Acknowledgement: The work performed was supported by the European Commission under the 7th Framework Programme, NMP/2007-2013, through the Project BIOGO, contract number CP-IP 604296.

Enhanced oxygen vacancy formation in cation doped bulk Cr2O3

249th National Meeting (2015)

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