Oxygen vacancy formation energy in Pd-doped ceria: A DFT+U study

Abstract

Using the DFT+U method, i.e., first principles density functional theory calculations with the inclusion of on-site Coulomb interaction, the effects of Pd doping on the O vacancy formation energy (E(vac)) in CeO(2) has been studied. We find that E(vac) is lowered from 3.0 eV in undoped ceria to 0.6 eV in the Pd-doped compound. Much of this decrease can be attributed to emerging Pd-induced gap states above the valence band and below the empty Ce 4f states. These localized defect states involve the Pd ion and its nearest neighbors, which are also the main acceptors of the extra electrons left on reduction. The effect of the Pd dopant on the geometric structure is very modest for CeO(2) but considerable for CeO(2-x).

Direct CO Oxidation by Lattice Oxygen on Zr-Doped Ceria Surfaces

“…They are two stable low index surfaces and have been extensively studied [23,24]. It is known that CO takes the Ce site on the clean CeO 2 (111) surface but the adsorption energy is very small, 3.9 kcal/mol [25] from GGA calculations and 4.2 kcal/mol from the present GGA ?…”

On the interaction of Mg with the (111) and (110) surfaces of ceria

“…4 we show the atomic structure of the bare CeO 2 (111) and (110) surfaces. 45,46 The (111) surface has 7 coordinate surface Ce and 3 coordinate surface oxygen, with Ce-O distances slightly shortened over the bulk oxide, at 2.36 Å . In the surface layer, the (110) surface has 6 coordinate Ce and surface oxygen are 3 coordinate, with surface Ce-O distances of 2.32 Å .…”

“…To describe oxide reduction in CeO 2 requires an approach such as DFT + U 66 or hybrid DFT. 46,47 The application of DFT + U to ceria is well known and will not be discussed here. [10][11][12][13][14][15][16][17][20][21][22][39][40][41][42][43][44] In our work, the U parameter is 5 eV on Ce 4 f states.…”

“…Also, catalysts based on mixed MgO-CeO 2 supports and Mg doping have been proposed for many different reactions. [39][40][41][42][43] First principles simulations have been applied to study the atomic level properties of undoped [13][14][15][16][17] and doped ceria surfaces, 38,[44][45][46][47][48] to rationalise experimental findings and determine the impact of the dopant on the properties of ceria. Dopants include Au, 36,37 Zr, 26 Ti, 38 La, 44 Pt, 45 Pd 46,47 and Ni.…”

“…25% exact exchange is applied and this is a universal parameter. The screened exchange functional of Heyd-Scuseria-Ernzerhof (HSE) is used, 46,47 with a universal screening parameter of 0.2/Å . Due to the large computational expense of hybrid DFT calculations in a plane wave basis set, we limit hybrid DFT to the (2 Â 2) surface supercell expansion of the (111) surface, providing a check on the performance of DFT + U; applications of hybrid DFT to ceria can be found in recent papers.…”