O vacancies on steps on the CeO2(111) surface

Assessment of PBE+U and HSE06 methods and determination of optimal parameter U for the structural and energetic properties of rare earth oxides

Rare earth oxides are attracting increasing interest as a relatively unexplored group of materials with potential applications in heterogeneous catalysis and electrocatalysis; therefore, a credible and universal computational approach is needed for modeling their reactivity. In this work, we systematically assessed the performance of the PBE+U method against the results of the hybrid HSE06 method with respect to the description of structural parameters and energetic properties of the selected hexagonal lanthanide sesquioxides and the cubic fluorite-type cerium dioxide. In addition, we evaluated the performance of PBE+U in describing the electronic structure and adsorption properties of the CeO₂(111) and Nd₂O₃(0001) surfaces. The HSE06 method reproduces rather well the lattice parameters and selected energetic properties with respect to the experimental values. The PBE+U method is able to reproduce the results of HSE06 or the experimental values only if the U parameter is selected from an appropriate range of values. The U value around 3 eV gives the best description of the lattice parameters of most bulk oxides. 2 eV-3 eV is also found to be the optimal range of U for the reaction energies of bulk La₂O₃, Ce₂O₃, Nd₂O₃, Er₂O₃, and Ho₂O₃. U = 1 eV gives the best results for Pr₂O₃, Pm₂O₃, Eu₂O₃, Tm₂O₃, and Lu₂O₃, whereas Gd₂O₃ could not be accurately described by the PBE+U method. The U values (∼3 eV) found optimal for most bulk oxides also work well in the calculations of adsorption of small molecules on Nd₂O₃(0001) and CeO₂(111), although larger U values are required to obtain sufficient localization of 4f electrons.

Structure and reducibility of yttrium-doped cerium dioxide nanoparticles and (111) surface

Using periodic density functional calculations, we studied the local structure and preferred locations of yttrium cations and oxygen vacancies in Y-doped cerium dioxide. We employed three kinds of models – a slab of the CeO₂(111) surface and two ceria nanoparticles of different sizes and shapes. In the slab models, which represent the (111) surface of ceria and the corresponding extended terraces on the facets of its nanoparticles, Y³⁺ cation dopants were calculated to be preferentially located close to each other. They tend to surround a subsurface oxygen vacancy that forms to maintain the charge balance. Such general behavior was not found for the nanoparticle models, in which structural flexibility and the presence of various low-coordinated surface centers seem to be crucial and suppress most of the trends. Configurations with four Y³⁺ cations were calculated to be particularly stable when they combined two of the most stable configurations with two Y³⁺ cations. However, no clear trend was found regarding the preferential spatial distribution of the Y³⁺ pairs – they can be stable both in isolation and close to each other. In general, doping by yttrium does not notably change the reducibility of ceria systems but selectively facilitates the formation of oxygen vacancies at the ceria surface in comparison with pristine ceria. Yttrium cations also slightly increase the basicity of the nearby oxygen centers with respect to a stoichiometric ceria surface.

Energetics and mutual locations of Y³⁺ ion dopants and O vacancies in CeO₂ nanomaterials relevant to catalysis have been studied.

Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

Nanomaterials coated with atomically dispersed platinum on ceria are structurally dynamic and show high potential for applications in fuel cells.

Creating single-atom Pt-ceria catalysts by surface step decoration

Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. Here we show by combining photoelectron spectroscopy, scanning tunnelling microscopy and density functional theory calculations that Pt single atoms on ceria are stabilized by the most ubiquitous defects on solid surfaces--monoatomic step edges. Pt segregation at steps leads to stable dispersions of single Pt(2+) ions in planar PtO4 moieties incorporating excess O atoms and contributing to oxygen storage capacity of ceria. We experimentally control the step density on our samples, to maximize the coverage of monodispersed Pt(2+) and demonstrate that step engineering and step decoration represent effective strategies for understanding and design of new single-atom catalysts.

Reduced ceria nanofilms from structure prediction

Experimentally, Ce2O3 films are used to study cerium oxide in its fully or partially reduced state, as present in many applications. We have explored the space of low energy Ce2O3 nanofilms using structure prediction and density functional calculations, yielding more than 30 distinct nanofilm structures. First, our results help to rationalize the roles of thermodynamics and kinetics in the preparation of reduced ceria nanofilms with different bulk crystalline structures (e.g. A-type or bixbyite) depending on the support used. Second, we predict a novel, as yet experimentally unresolved, nanofilm which has a structure that does not correspond to any previously reported bulk A2B3 phase and which has an energetic stability between that of A-type and bixbyite. To assist identification and fabrication of this new Ce2O3 nanofilm we calculate some observable properties and propose supports for its epitaxial growth.

Electronic storage capacity of ceria: role of peroxide in Aux supported on CeO2(111) facet and CO adsorption

Au adsorbs on CeO₂(111) with an O vacancy to form Au^δ−, which is not favorable for CO adsorption. After peroxide formed on CeO₂(111) with an O vacancy, Au is oxidized to Au^δ+, which improves CO adsorption on Au/CeO₂, where CeO₂ acts as an electron buffer.

Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems

Binary and ternary PrO_xand CeO_xfilms grown on Si(111) are most versatile systems available in a variety of stoichiometries and surface structures.

The structure and stability of reduced and oxidized mononuclear platinum species on nanostructured ceria from density functional modeling

The most stable neutral and ionic mononuclear platinum species and their positions on a ceria nanoparticle under different conditions are identified.

An efficient noble metal-free Ce–Sm/SiO2 nano-oxide catalyst for oxidation of benzylamines under ecofriendly conditions

Nanosized Ce–Sm/SiO₂ mixed oxide is an efficient reusable noble metal-free catalyst for aerobic oxidation of benzylamines.