Tuning the charge state of Ag and Au atoms and clusters deposited on oxide surfaces by doping: a DFT study of the adsorption properties of nitrogen- and niobium-doped TiO2 and ZrO2

The charge state of Ag and Au atoms and clusters (Ag4 and Au4, Ag5 and Au5) adsorbed on defective
TiO2 anatase(101) and tetragonal ZrO2(101) has been systematically investigated as a function of oxide
doping and defectivity using a DFT+U approach. As intrinsic defects, we have considered the presence
of oxygen vacancies. As extrinsic defects, substitutional nitrogen- and niobium-doping have been
investigated, respectively. Both surface and sub-surface defects and dopants have been considered.
Whereas on surfaces with oxygen vacancies or Nb-doping, atoms and clusters may become negatively
charged, N-doping always leads to the formation of positively charged adsorbates, independently of the
supporting material (TiO2 or ZrO2). This suggests the possibility to tune the electronic properties of
supported metal clusters by selective doping of the oxide support, an effect that may result in complete
changes in chemical reactivity.