Several different charge transfer and Ce³⁺localization scenarios for Rh–CeO₂(111)

Abstract

We present DFT+U based electronic structure calculations in a p(3 Â 3) slab supercell, for low coverages of atomically dispersed Rh interacting with the CeO 2 (111) surface, comparing Rh as an adatom, and as a dopant substituted into the surface layer. We find that, energetically, a Rh atom approaching a ceria(111) surface with both sparse O and Ce vacancies present strongly prefers to heal the Ce vacancies, but next it prefers to adsorb on a stoichiometric region rather than healing an O vacancy. In the adatom system, Rh is oxidized by electron transfer to a 4f orbital on one Ce ion in the surface layer, which is then nominally converted from Ce 4+ / Ce 3+ (i.e. Rh adatoms are single donors). We show that there are a number of different local minima, with Ce 3+ localization at 1 st , 2 nd or 3 rd nearest neighbour Ce sites. The second neighbour is the most stable, but all are close in energy. In the Rh-doped system (Rh replaces Ce), Rh is oxidized by charge transfer to neighbouring O atoms, and Rh doping leads to deep acceptor and donor states. Rh is not stable in the O sublattice. Moreover, based on vacancy formation energies, we find that oxygen vacancy formation is strongly enhanced in the vicinity of Rh dopants, but slightly suppressed in the vicinity of Rh adatoms.

Stability and Temperature-Induced Agglomeration of Rh Nanoparticles Supported by CeO2

“…On the other hand, the various reduction state of a reducible oxide can also influence the agglomeration process because O vacancies of the oxide support stabilize the dispersed state. 74−77 However, the effect here is controversial because, according to some theoretical work, Rh does not tend to sit inside the vacancies; 78 moreover, subsurface vacancies are more stable than the ones in the topmost layer. 79 In some work, enhanced O-storage capacity by supercharging (presence of surface superoxide ions (O 2 − )) on the surface was concluded for small CeO 2 particles, 80−82 while the photocatalytic activity of ceria was attributed to the formation of superoxide radicals.…”

Self‐Regenerative Property of Nanocrystalline Ce0.89M0.11O2−y (M=Pd, Rh) Mixed Oxides

“…[10] An ideal system should be characterised by high solubility of metal ions in the oxide matrix (at moderate temperature) to enable the regeneration step in oxidising atmosphere but also a relatively strong bonding between metal particles and the oxide support to prevent uncontrolled sintering of the metal phase in the reducing atmosphere. Ab initio calculations based on DFT are used to study the adsorption of metal nanoparticles and aggregation processes of atoms on non-metallic surfaces [13][14][15][16] and may be a valuable tool to be sought for new metal-oxide systems having the self-regenerative property.…”

First-principles study of the effect of dopants (Pd, Ni) on the formation and desorption of T2O from a Li2TiO3 (001) surface

“…8, the desorption energies of T 2 O molecules are $0.30 and $0.27 eV on the two positions of the Pd-T-Li 2 TiO 3 surface, and $0.48 and $0.38 eV on the two positions of the Ni-T-Li 2 TiO 3 surface. In contrast with the value of 1.956 eV for the Li 4 SiO 4 surface, 36 the desorption energies of T 2 O molecules in the doped systems are acceptable. The energy required for desorption varies greatly, which may be due to the different dopant atom.…”

“…To further investigate the catalytic mechanism of the dopants on T 2 O formation, we calculated the effect of dopant atoms on the formation energy of O vacancies, according to previous studies. 35,36 The O atoms closest to the dopant atom and the Ti atom substituted on the surface by DA were selected for the study. We dene the O vacancy formation energy for Li 2 TiO 3 (001) surface as 24…”