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Computing accurate rate constants for catalytic events occurring at the surface of a given material represents a challenging task with multiple potential applications in chemistry. To address this question, we propose an approach based on a combination of the rare event sampling method called adaptive multilevel splitting (AMS) and ab initiomolecular dynamics. The AMS method requires a one-dimensional reaction coordinate to index the progress of the transition. Identifying a good reaction coordinate is difficult, especially for high dimensional problems such as those encountered in catalysis. We probe various approaches to build reaction coordinates such as support vector machine and path collective variables. The AMS is implemented so as to communicate with a density functional theory-plane wave code. A relevant case study in catalysis, the change of conformation and the dissociation of a water molecule chemisorbed on the (100) γ-alumina surface, is used to evaluate our approach. The calculated rate constants and transition mechanisms are discussed and compared to those obtained by a conventional static approach based on the Eyring–Polanyi equation with harmonic approximation. It is revealed that the AMS method may provide rate constants that are smaller than those provided by the static approach by up to 2 orders of magnitude due to entropic effects involved in the chemisorbed water molecule.

Transition aluminum oxides, such as γ-Al2O3or alumina, are widely used in many different technical applications that rely on the surface reactivity of this material at the solid liquid interface. The speciation of surface sites of this material confronts several obstacles. On the one hand, alumina is a poorly crystalline oxide, thus allowing for a limited amount of empirical structural information for an important number of surface sites with different trends in reactivity and, on the other hand, it is a metastable material. In this work, we show several ways in which the multisite complexation model, combined with atomistic information from density functional theory and ab initio molecular dynamics (AIMD), can manage to perform speciation calculations of γ-Al2O3surface sites at the solid liquid interface. Although the results are in good qualitative agreement with experimental titration curves, and they can serve as a guide for the interpretation of the reactivity of this material at the initial stages of an impregnation experiment and chemical weathering phenomena, this work highlights the need of more complex AIMD simulations to accurately model these phenomena in γ-Al2O3surface/liquid interfaces.

Solid sulfide electrolytes hold great promise for making all-solid state batteries a reality. Therefore, their wet chemical synthesis has become increasingly important in recent years due to various benefits such as scalability and versatility. The Li3PS4electrolyte has a relatively high ionic conductivity (≈10–4S cm–1at 25 °C) and can be synthesized in various organic solvents by reacting Li2S and P2S5. It is well-known that the choice of the solvent is critical for the synthesis. Herein, we investigated several new organic polar solvents such as sulfur-based solvents (propanethiol, thiolane, and thiophene), amines, and carbonyls (esters, carbonates, ketones) for the synthesis of Li3PS4. The relationship between the ability to perform the reaction, the ionic conductivity, and the solvents’ characteristics revealed that the electronic density of the polar function plays a key role. The results of this study can be used as a guideline to select new synthesis solvents. We also identify a particular solvent, isobutyl isobutyrate (IBIB), which allows the decomposition of the corresponding Li3PS4solvato-complex below the boiling point of the solvent with one of the highest reported ionic conductivities for the wet chemical method (2.1 × 10–4S cm–1at room temperature).

The interaction of two common oxygenates, ethylene glycol (EG) and acetic acid (AA), with the main exposed (100) and (110) surfaces of γ-Al2O3are investigated by quantifying the thermochemistry of the drying process. Using density functional theory (DFT) calculations, we determine adsorption free energies and identify the adsorption modes and sites for both molecules interacting with the (100) and (110) surfaces of γ-Al2O3at various coverages. While the affinity of both molecules is stronger for the (100) surface after drying, EG is more strongly adsorbed on alumina surfaces than AA. EG preferentially interacts through hydrogen bonds on the hydroxyl nests of the (100) and (110) surfaces, while it may also interact through Al–O bonds on the (110) surface at low coverage. AA is predominantly deprotonated and interacts as acetate anions through hydrogen bonds on the (110) and (100) surfaces and through Al–O bonds on the (100) surface at low coverage. We then propose a quantitative comparison of the interaction of Co2+hexaaquo precursor with the same γ-Al2O3surfaces. The adsorption configurations of the two organic molecules which may hinder the epitaxial growth of cobalt oligomers on alumina surfaces are identified. However, the thermodynamic analysis shows that EG and AA are less stable than the Co precursors after drying. The strong stabilization of Co precursors is attributed to its epitaxial relationship with the dried alumina surfaces as found in [Angew. Chem. Int. Ed.2015, 54, 6824–6827] and also to a favorable entropy change during the drying process (vapor release and nitrate counterion decomposition in the gas phase). We finally discuss how these effects can be circumvented by changing the conditions of preparation and drying.

Using density functional theory calculations, we investigate the surface deposition of O on Co(111) terrace and Co(221), Co(112) step surfaces in realistic Fischer–Tropsch (FT) reaction conditions. We compared these results with previous works for C deposition on Co surfaces. Furthermore, we compute the activation barriers of C and O diffusion in subsurface Co(111) sites at different surface coverages. According to our results, thermodynamics and kinetics exhibit opposite trends, and the final cause of the catalyst deactivation is the outcome of a trade-off between the two effects. In particular, we show that the surface deposition of O is thermodynamically favorable. However, in order to increase a surface coverage beyond 1 ML, the O atom should first diffuse within the Co sublattice, which is kinetically hindered compared to subsurface C diffusion. However, the formation of an oxide shell around Co is possible from a thermodynamic and a kinetic point of view, particularly in the presence of an oxygen surface vacancy allowing the outward relaxation of Co atom (Kirkendall-type process). Lastly, we discuss in which circumstances the formation of this O overlayer prevails over the deactivation by the deposition of C resulting from a subtle interplay between the kinetics of the FT reaction steps.

We establish a thermodynamic model correlating the carbon deposition and desorption energies on cobalt surfaces with the temperature, the CO/H2ratio, and the Anderson–Schulz–Flory (ASF) distribution in the Fischer–Tropsch (FT) synthesis reaction. Density functional theory (DFT) calculations predict that the surface sites of Co particles, whether located on terraces or steps, are covered by carbon species in FT reaction conditions unless extremely high H2/CO ratios are used. The graphene-covered Co(111) surface is the most stable system. At low ASF coefficient, the Co(111) surface undergoes a strong reconstruction associated with the insertion of C in subsurface sites. At high ASF coefficient, the Co(111) surface is covered by oligomeric C species which may be seen as either long chain alkane or graphene precursors. This theoretical work gives crucial insights into the link between the composition and structures of Co surfaces in FT reaction conditions. Furthermore, it highlights that the existence of purely metallic sites, whether located on terraces or steps, is questioned in long-run FT synthesis.

The development of original nanoparticle size and shape requires a detailed knowledge and rationalization of the formation mechanism. A consolidated mechanism of γ-AlOOH boehmite nanorod formation in aqueous hydrothermal conditions is proposed based on an advanced characterization of the final product, kinetic studies, and surface energy calculations. Boehmite nanorods with a width of about 10 nm and more than 100 nm in length are obtained in slightly acidic conditions from Al(III) molecular precursors at temperature higher than 150 °C. The identification of protoboehmite as an intermediate in the kinetic study combined with the low solubility of aluminum in reacting conditions and the presence of stacking defects in the rods is indicative of an aggregation mechanism. Electron diffraction studies show that the crystallites are oriented in the nanorods with a [001] preferential growth direction. Using DFT calculations, we demonstrated that the nanorod morphology is not the expected thermodynamically stable one in these experimental conditions. An explanation of the oriented aggregation of primary particles is proposed based on an eased depletion of the solvation water molecules of the (001) surface compared to the other surfaces.