Oxide reducibility is an important property in catalysis by metal-oxides, for instance in reactions following the Mars-van Krevelen mechanism. Usually, oxides are classified based on their bulk reducibility, i.e. the tendency to loose oxygen, generating excess electrons in the material. SiO2, MgO, and ZrO2 are considered non-reducible oxides, while TiO2, CeO2, and Fe2O3 are typical reducible oxides. However, the reducibility of an oxide can be substantially modified, either by generating nanostructures (nanoparticles, nanowires, or nanofilms) or by creating an interface between the oxide and a metal. We will use ZrO2 as a prototype of non-reducible oxides, and we will show how the properties, and in particular the reducibility, of the material can be tuned by nanostructuring or by depositing metal particles on ZrO2 (classical heterogeneous catalysts) or, as an alternative, by growing ZrO2 films on metal surfaces (inverse catalysts). We designed models of these systems, and by means of first principle calculations we analysed a key descriptor of the oxide reducibility, the formation energy of an oxygen vacancy. We also considered other reduction processes, including exposure to hydrogen. The ZrO2 reducibility is dramatically modified when the oxide is prepared in form of nanoparticles, or is interfaced with a metal. The consequences are not only on the chemical activity of the oxide surface, but also on other properties, such as the magnetic behaviour: while bulk zirconia is non-magnetic, reduced zirconia nanoparticles are ferromagnetic. We will also show, using graphitic-like ZnO layers deposited on Cu, Ag, and Au supports as an example, the potential of controlling metal/oxide interfaces for the design of new catalysts with tailored properties.

Catalysts design from first principles: Modifying oxide reducibility by nanostructuring and metal/oxide interfaces

2019 Fall National Meeting

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