Rare-earth oxides (REOs) possess a remarkable intrinsic hydrophobicity, making them candidates for a myriad of applications. Although the superhydrophobicity of REOs has been explored experimentally, the atomistic details of the structure at the oxide-water interface are still not well understood. In this work, we report a density functional theory study of the interaction between water and CeO2, Nd2O3, and α-Al2O3 to explain their different wettability. The wetting of the metal oxide surface is controlled by geometric and electronic factors. While the electronic term is related to the acid-base properties of the surface layer, the geometric factor depends on the matching between adsorption sites and oxygen atoms from the hexagonal water network. For all the metal oxides considered here, water dissociation is confined to the first oxide-water layer. Hydroxyl groups on α-Al2O3 are responsible for the strong oxide-water interaction, and thus, both Al- and hydroxyl-terminated wet. On CeO2, the intrinsic hydrophobicity of the clean surface disappears when lattice hydroxyl groups (created by the reaction of water with oxygen vacancies) are present as they dominate the interaction and drive wetting. Therefore, hydroxyls may convert a intrinsic nonwetting surface into a wetting one. Finally, we also report that surface modifications, like cation substitution, do not change the acid-base character of the surface, and thus they show the same nonwetting properties as native CeO2 or Nd2O3.

Many common density functional theory methods used in the study of adsorption on metals lack dispersion contributions. Formulations like the random phase approximations would mitigate this error, but they are computationally too expensive. Therefore, semiempiric treatments based on dispersion coefficients turn out to be a practical solution. However, the parameters derived for atoms and molecules are not easily transferable to solids. In the case of metals, they cause severe overbinding as screening is not properly taken into consideration. Alternative ways to determine these parameters for metal surfaces have been put forward, but they are complex and not very flexible when employed to address low-coordinated atoms or alloys. In this work, we present a self-consistent, fast, and costless tool to obtain the dispersion coefficients for metals and alloys for pristine and defective surfaces. Binding energies computed with these parameters are compared to both the experimental and theoretical values in the literature thus demonstrating the validity of our approach.

We have studied the properties of bulk and different surfaces of rutile oxides, IrO2, RuO2, SnO2, and TiO2, and their binary compounds by means of density functional theory. As mixtures are employed in many applications, we have investigated the solubility, segregation, and overlayer formation of one of these oxides on a second metal from the series, as these aspects are critical for the chemical and electrochemical performances. Our results show that the bulk solubility is possible for several combinations. The electronic structure analysis indicates the activation of Ir states in Ir(x)Ti(1-x)O2 mixtures when compared to the parent IrO2 compound or the reduction in the band gap of TiO2 when Sn impurities are present. Segregation and oxygen-induced segregation of the second metal for the most common surfaces show a great extent of possibilities ranging from strong segregation to antisegregation, which depends on the oxygen ambient. The interaction of guest rutile overlayers on hosts is favourable and a wide range of growth properties (from multilayer formation to tridimensional particles) can be observed. Finally, a careful comparison with experimental information is presented, and for those cases where no data is available, the computed database can be used as a guideline by experimentalists.

Theoretical simulations of systems that represent heterogeneous catalysts constitute one of the main tools in the research for new catalytic materials. Theory plays a role in the three stages of the development ladder: characterisation, understanding and prediction. Due to the complexity of the computational methods, there is a strong need to integrate different models and cover the relevant scales in heterogeneous catalysis. This requirement constitutes an important drawback as scientists need training in several aspects of the problem including chemical, physical and engineering views of the modelling while keeping the experimental and industrial interests and needs in perspective. Here we present some of the latest developments in the field of theoretical simulations at the microscopic level while illustrating suitable examples that show how theory can shed light on several aspects of characterisation, activity, selectivity and long-term stability.

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