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 TiO₂and ZrO₂

Abstract

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.

Effect of reducible oxide–metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

“…Noble metal nanoparticles (NPs) supported on oxide surfaces are widely used in heterogeneous catalysis [1][2][3][4][5][6][7][8][9] and photocatalysis, where they can effectively inhibit the recombination of photogenerated electron-hole pairs in photocatalytic processes, 10,11 and at the same time facilitate/enhance the catalytic activity. 11,12 Among oxide supports for metal NPs, titanium dioxide (TiO 2 ) is known for showing significant promoting effects of the NPs' catalytic activity.…”

“…13,20,[23][24][25] To improve the performance of existing catalysts and photocatalysts, a detailed understanding of all the factors that can affect their activity is crucial. To this end, numerous theoretical and experimental studies have examined the interaction between the metal NPs and oxide surfaces, 9,[26][27][28] as well as the mechanisms of nucleation, growth, and diffusion of supported metal NPs. [29][30][31] As a typical reducible oxide, TiO 2 usually contains "excess" electrons (i.e., electrons in excess of those that a) Author to whom correspondence should be addressed.…”

“…Several studies have already made significant contributions to such an understanding. 9,22,28,[33][34][35][36] To obtain further insights, in this work we have used first principles density functional theory (DFT) calculations to analyze the influence of surface excess electrons on the structure, energetics, and reactivity of Pt and Au atoms, dimers, and trimers adsorbed on the (101) surface of anatase TiO 2 . Besides being useful model systems for understanding the different behaviors of Pt and Au NPs on stoichiometric and reduced TiO 2 , such small clusters are currently of great interest in catalysis because of their unique properties and lower costs as well.…”

“…51 It was also shown that the interaction of Au clusters with anatase (101) is weaker than that of Pt clusters, 5 and the contributions of van der Waals (vdW) forces can be significant. 9 In this work, the reduced support is modeled by considering anatase (101) slabs that include donor dopants, such an adsorbed hydrogen atom or a substitutional Nb impurity, and the reactivity of the supported Pt and Au clusters is probed by focusing on their interaction with CO and co-adsorbed O 2 .…”

Oxide‐Supported Gold Clusters and Nanoparticles in Catalysis: A Computational Chemistry Perspective

“…[41] The role of intrinsic and extrinsic defects in the oxide in determining the charge of atomic Au adsorbates was investigated by Schlexer et al in the cases of TiO 2 anatase (101) and tetragonal ZrO 2 (101) using a DFT + U approach. [42] As intrinsic defects, neutral oxygen vacancies were considered, while as extrinsic defects, substitutional p-doping with nitrogen or n-doping with niobium was considered. The dependence on the defect's location (surface or subsurface) was also investigated.…”