Systematic Characterization of Electronic Metal–Support Interactions in Ceria-Supported Pt Particles

Electronic metal–support interactions affect the chemical and catalytic properties of metal particles supported on reducible metal oxides, but their characterization is challenging due to the complexity of the electronic structure of these systems. These interactions often involve different states with varying numbers and positions of strongly correlated d or f electrons and the corresponding polarons. In this work, we present an approach to characterize electronic metal–support interactions by means of computationally efficient density functional calculations within the projector augmented wave method. We describe Ce3+ cations with potentials that include a Ce4f electron in the frozen core, overcoming prevalent convergence and 4f electron localization issues. We systematically explore the stability and chemical properties of different electronic states for a Pt8/CeO2(111) model system, revealing the predominant effect of electronic metal–support interactions on Pt atoms located directly at the metal–oxide interface. Adsorption energies and the reactivity of these interface Pt atoms vary significantly upon donation of electrons to the oxide support, pointing to a strategy to selectively activate interfacial sites of metal particles supported on reducible metal oxides.

: Comparison of energy differences ΔE of electronic states calculated using the 4f-core scheme and the 4f-valence scheme.Energy differences are calculated separately for each number of electrons transferred.The numbers after the number of electrons transferred N TE specify the positions of N surface Ce 3+ cations according to the labels in Fig. 1.In parenthesis are indicated the spin orientation of every Ce 3+ cation obtained at the 4fvalence-su level, where '↑' denotes spin up and '↓' is spin down.Empty circles are energy differences obtained for spin-restricted calculations while solid circles are energy differences obtained for spin-unrestricted calculations.Energy differences are calculated separately for each number of transferred electrons TE.

Figure S3:
Relative energies  $%&)*#"+'" and  $%&'(!" of all possible electronic states calculated for the Pt8/CeO2 system with 0 to 2 electrons transferred from Pt8 to the CeO2 support with the supercell size 4×4.Black bars correspond to  $%&'(!" values obtained using the Ce4f-core potential (with Ce4f electrons in the core of selected Ce atoms) and spin-restricted calculations.Red bars correspond to  $%&)*#"+'" values obtained using the Ce4f-valence potential only (without fixed core Ce4f electrons) and spin-unrestricted calculations.Numbers next to red bars specify positions of the Ce 3+ cations as labeled in Figure S1.Dashed lines connect values for states with Ce 3+ cations in the same positions calculated using the 4f-core and 4f-valence schemes.All values are also provided in Table S2.S2: Energy differences of selected electronic states of the 4×4 slab model obtained using the 4f-core scheme and the 4f-valence scheme.Energy differences are calculated separately for each number of transferred electrons.The numbers after the number of transferred electrons N TE specify the positions of N surface Ce 3+ cations according to the labels in Fig. S1.In parenthesis are indicated the spin orientation of every Ce 3+ cation obtained at the 4f-valence spin unrestricted level, where '↑' denotes spin up and '↓' is spin down.

Figure S7:
Comparison of total density of states of Pt8 cluster for different supercell sizes for 0 to 2 transferred electrons (a, b and c, respectively).For 2 TE, the label 1,5 for the 4×4 supercell (Figure S1) was chosen because of its similar chemical environment to the state used for the supported Pt8 on the 3x3 supercell (Figure 1).The most stable electronic states is evaluated in the 3×3 supercell (with Ce 3+ in position Ce-5 for 1 TE and Ce-1/Ce-5 for 2 TE).The positions of Ce 3+ cations in the 4×4 supercell were chosen to be the same with respect to the Pt8 cluster as in the 3×3 supercell.Table S10: Adsorption energies (in eV) of H, H2O, OH, and CO adsorbates on the interface Pt-8 and the second-layer Pt-1 adsorptions sites, at 0 to 3 transferred electrons, calculated spinrestricted.The positions of Ce 3+ cations described by the Ce4f-core potential are Ce-5 for 1 TE, Ce-1,5 for 2 TE, and Ce-1,5,6 for 3 TE.

Figure S1 :
Figure S1: Structural model of a Pt8 cluster supported on the CeO2(111) surface.Dashed lines delimit the 4×4 supercell used.Pt, Ce and O atoms are depicted in grey, beige, and red, respectively.Numbers in bold are labels of Ce atoms according to their position relative to the Pt8 cluster.Ce-5 atom is located below the Pt8 cluster.Symmetrically equivalent Ce atoms have the same label.Numbers in italics are labels of the Pt atoms.

Figure S2 :
Figure S2: Dispersion of energy difference values obtained with 4f-core and 4f-valence potentials.Empty circles are energy differences obtained for spin-restricted calculations while solid circles are energy differences obtained for spin-unrestricted calculations.Energy differences are calculated separately for each number of transferred electrons TE.

Figure S4 :
Figure S4: Density of states projected on the Pt atoms of the Pt8 cluster supported on CeO2(111) for the most stable electronic states with a) -one, b) -two and c) -three electrons transferred from the cluster.The methodology to calculate the electronic structure is specified by the color of the lines.

Figure S5 :
Figure S5: Density of states projected on the Pt atoms of the Pt8 cluster for 0 to 3 electrons transferred from it, taking the most stable state in each case calculated with the 4f-valence scheme.Energy values are calculated with respect to the Fermi level, marked by a vertical dashed line.

Figure S6 :
Figure S6: Comparison of total density of states of Pt8 cluster for different positions of Ce 3+ cations for 1 to 3 electrons transferred (a, b and c, respectively).The position of Ce 3+ cations in the legends are depicted in Fig. 1.

Table S3 :
Ce-O bond distances, comparing 4f-core and 4f-valence potentials for different states with different numbers of Ce 3+ cations.The left side of the table shows Ce-O distances with surface oxygen atoms and the right-side shows Ce-O distances with sub-surface oxygen atoms bonded to the Ce atom identified by the labels described in Figure1a.All distances are in Angstrom (Å).

Table S4 :
Integrated total, sp-orbitals and d-orbitals values of density of states (DOS) of the Pt8 cluster at 0, 1, 2 and 3 transferred electrons.

Table S5 :
Bader charges of Pt atoms in the CeO2(111)-supported Pt8 cluster for 0 to 3 transferred electrons.The most stable electronic state is evaluated in each case, comparing values obtained with Ce4f-core and Ce4f-valence potentials.The cluster atoms are labelled as shown in Fig.1.

Table S6 :
Bader charges of Pt atoms in the CeO2(111)-supported Pt8 cluster, comparing different positions of Ce 3+ cations for different number of transferred electrons.The numbers next to Ce indicate the position of formed Ce 3+ cations and the Pt atoms labelled as indicated in Fig. 1.

Table S7 :
Bader charges of Pt atoms in the CeO2(111)-supported Pt8 cluster for 0 to 2 transferred electrons on the 4×4 CeO2 slab.The most stable electronic state is evaluated in the 3×3 supercell, and the positions of Ce 3+ cations in the 4×4 supercell were chosen to be the same with respect to the Pt8 cluster as in the 3×3 supercell.All values were obtained using Ce4f-core potentials and spin-restricted calculations.The Pt atoms are labelled in FigureS1.

Table S8 :
CO adsorption energies (in eV) on the interface Pt-8 and second-layer Pt-1 sites of Pt8/CeO2 for the electronic states with 0 to 3 transferred electrons (TE) from Pt8, calculated at several levels of theory, including spin-restricted (sr) and spin-unrestricted (su) calculations using the 4f-core potential for describing Ce 3+ cations, and spin-unrestricted calculations using the 4fvalence potentials only.Missing values indicate that those states could not be converged to at the corresponding level of theory.