First-row transition metal atoms adsorption on rutile TiO2(110) surface

Abstract

We performed periodic DFT calculations for adsorption of metal atoms on a perfect rutile TiO 2 (110) surface (at low coverage, h = 1/3) to investigate the interaction of an individual metal atom with TiO 2 and to compare it with a study previously done on MgO(100). We considered partial period of Mendeleev's table from K to Zn. The overall evolution of the adsorption energies shows two maxima as for MgO (100). Two main differences, however, exist: the adsorption energy is much stronger and the first maximum is enhanced relative to the second one. This is attributed to the reducibility of the surface titanium cation. When the adsorbed metal is electropositive, it is oxidized under adsorption transferring electrons to titanium cations. We present the effect of introducing a Hubbard term to the gradient-corrected approximation band-structure Hamiltonian (GGA ? U). The introduction of a reasonable Hubbard correction preserves the trends and allows localizing the electron of the reduction on Ti atoms in the near surface region. Finally, our results conclude that for heavier M atoms of the period, insertion is energetically favored relative to adsorption.

Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation

“…Furthermore, it was also observed that our computed adsorption energies are reasonably similar to the values described in the literature for the adsorption of SAC on the irreducible alumina (Al 2 O 3 ) surface, [22a, b, 51] but significantly weaker than those found for the reducible rutile (TiO 2 ) support [23] . As such, the adsorption of a single Pd, Pt or Cu atom on the ‐Al 2 O 3 support is, respectively associated with an energy of −1.35, −2.20 and −0.70 eV, [22a, b, 51] whereas our calculations on the amorphous silica surface give rise to values of −1.21, −2.62 and −0.78 eV.…”

“…From the current literature it can nonetheless be concluded that the strength by which these transition metal atoms adsorb on the surface is strongly driven by the above‐mentioned concept of SMSI. Accordingly, the adsorption of d‐transition metal atoms on defect‐free irreducible oxide supports (MgO, [20] SiO 2 [21] and Al 2 O 3 [22] ) will often be accompanied by less pronounced interactions than in the case of SMSI surfaces like TiO 2 [23] and CeO 2 [24] . While the metal‐support interactions in the non‐SMSI state often depend on a combination of effects such as van der Waals dispersion, polarization and sometimes orbital mixing, [20–21] the reducible character of TiO 2 and CeO 2 turns out to play a crucial role in the observed enhanced adsorption [22, 24] .…”

“…This reducible character facilitates a more pronounced charge transfer from the metal to the surface which enables the formed d‐metal cation to interact more strongly with the O 2− atoms of the surface in comparison to the neutral atom. Notwithstanding the diverse nature of the interactions, it appears that regardless of the type of support, the adsorption is usually accompanied by a changing electronic configuration of the metal [20–24] . This quenching of the spin moment is often related to the fact that upon formation of a bond between the metal and support, the outer s‐ electrons of the transition metal are promoted into the incomplete d‐shell in order to reduce the number of unpaired electrons.…”

Reducing the irreducible: Dispersed metal atoms facilitate reduction of irreducible oxides.

“…The adsorption of the first TM row metals, as well as Pd, Ir, Pt and Au, has been studied using GGA-DFT on both pristine and defected rutile TiO 2 (110) surfaces. 58,59 Contrary to the results obtained for ZrO 2 and MgO, the adsorption energies of the studied metal atoms in the TiO 2 vacancy are typically more endothermic than or roughly equal to the corresponding energies on the ideal surface. 59 Only Au and, when the Hubbard correction was introduced, Pt bound more strongly inside a surface vacancy than on the ideal surface, though Pd and Ir were also noted as borderline cases.…”

Toward better understanding of the support effect: Test cases for CO dissociation on Fen/TiO2(1 1 0), n = 4, 5

“…Our calculations are periodic in three dimensions and we imposed a vacuum distance of 13 Å, which is large enough to avoid any interaction between two successive slabs. The model consists of nine atomic layers slab (three Ti 2 O 4 layers) of rutile oriented in the (110) direction, see Figure 5 [15,24,25]. We considered a double cell p(2x3) with a = 13.12 Å and b = 9.19 Å.…”