ZrO2 Nanoparticles: a density functional theory study of structure, properties and reactivity

The atomic structure, thermodynamic stability and electronic structure of a series of zirconia nanoparticles in the range of 0.9 and 2 nm in size have been investigated by means of the density functional theory (DFT)-based calculations. We show that the calculated formation energies scale linearly with the size of the nanoparticles. The calculated formation energies of neutral oxygen vacancies are considerably smaller than those in extended surfaces. In this respect, nanostructuring can be substantial for tuning the reactivity of zirconia and its reducibility. Also, the low-coordinated sites introduce defective states in the electronic structure reducing the effective band gap. This results in enhanced interaction with deposited particles as well as in modified catalytic and possibly photocatalytic activity. This has been investigated by considering (1) the adsorption of a single Au atom on different adsorption sites in the surfaces of the nanoparticles, leading indeed to a type of bonding that is not found on extended and stoichiometric zirconia surfaces and (2) the adsorption of an H-2 molecule which dissociates homolytically, with formation of two protons and two Zr3+ ions, while on the extended ZrO2 surface the preferred process is heterolytic dissociation into H+ and H- fragments.