We report ab initio molecular dynamics (AIMD) simulations of the (100) and (110) γ-Al2O3/water interfaces at 300 K, using two sets of supercell models for each surface and two time lengths of simulation (10 and 40 ps). We first show that the effect of liquid water on the vibrational frequencies of hydroxyl groups at the interface varies according to the type of surface. This trend is explained by two key parameters affecting the interaction of both surfaces with water: the nature of the OH groups (i.e., μ1-OH, μ1-H2O, μ2-OH, and μ3-OH) and H-bond network among surface OH groups. The hydroxylated (110) surface favors the local structuration of water at the interface and the solvation of its μ1-OH and μ1-H2O groups by water similarly as in bulk liquid water. By contrast, on the (100) surface, a stronger H-bond network among μ1-OH and μ1-H2O groups reduces the water/surface interaction. We illustrate also how the interfacial interacting sites are spatially organized on the surfaces by two-dimensional maps of O–H distances. On both surfaces, the interfacial water layer orientation is predominantly Hup–Hdown. For long AIMD simulation time, Grotthuss-like mechanisms are identified on the (110) surface.

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Using recent well-defined models of gamma-Al2O3 surfaces, we study the interaction of single Pd atoms with gamma-Al2O3 surfaces corresponding to realistic pretreatment conditions by means of density functional theory periodic calculations. For relevant hydroxylation states of the surface, we determine potential energy surfaces (PES) that depict the relationship between structure and interaction at the metal-oxide interface. This approach enables the determination of the low-energy diffusion paths of the adsorbed Pd species. We applied classical transition-state theory to derive the temperature-dependent hopping rate of Pd on gamma-Al2O3 surfaces. Our work provides new insight into the chemisorption and diffusion process of single Pd atoms on alumina and show that the binding energy and hopping rate of Pd atoms decrease as the surface OH coverage increases. These results offer new highlights on Pd cluster formation at the initial nucleation steps on gamma-Al2O3 surfaces.

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Ever stronger environmental concerns prompt the research in the area of heterogeneous catalysis to play an ever more crucial role to produce ever cleaner fuel from the refining of petroleum effluents. The catalytic active phase is often used in a dispersed state over a porous oxide material. This paper is a review of recent progress brought by periodic density functional theory (DFT) calculations in the area of two relevant industrial supported catalysts. We focus on two important supports used in the refining industry: anatase-TiO(2) and γ-alumina. According to the various reaction conditions, the presence of H(2)O, H(2) and H(2)S may change the surface states of the support. In particular, it is crucial to know and control the hydroxylation state depending on temperature and partial pressure of reactants (H(2)O, H(2), H(2)S). The support effects on the catalytic active phases are presented for MoS(2) particles, used in hydrodesulfurization catalysis, and for Pd particles, used in hydrogenation catalysis. It is shown how the wetting property and equilibrium morphology of the active phase depend on the support. A discussion on the impact for catalytic activities is provided.

Gauge origin independent calculations of nuclear magnetic shieldings in relativistic four-component theory Accurate theoretical near-equilibrium potential energy and dipole moment surfaces of HgClO and HgBrOThe correlation, relativistic, and vibrational contributions to the dipole moments, polarizabilities, and first and second hyperpolarizabilities of ZnS, CdS, and HgS

We establish a thermodynamic model correlating the carbon deposition and desorption energies on cobalt surfaces with the temperature, the CO/H 2 ratio, 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 H 2 /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. ■ INTRODUCTIONAlthough the Fischer−Tropsch (FT) synthesis has been known for almost a century, many questions remain open about fundamental issues such as the involved reaction mechanisms and the deactivation process. 1 These two issues are intimately linked since there is evidence that the reaction mechanism is site sensitive 2,3 (that is to say, that it strongly depends on the structure of the catalyst active phase) and that the presence of carbon produced by the dissociation of CO leads to a rearrangement of the catalyst structure 4,5 concomitant to its activity decay. 6 Hence, the interaction of C with Co-based FT catalysts is a key parameter impacting the FT reaction mechanism, and it is at the origin of the deactivation process.It is well-known that the interaction of C with Co has undesirable effects on the activity of the FT catalysts. 6,7 Experimental results show that there is an important buildup of carbon on the top of a used Co catalyst surface at the early stages of the FT synthesis reaction. 8 Moreover, experimental and theoretical results reveal that an amorphous C overlayer and a Co 2 C-like phase form during the FT reaction on Cobased catalysts. 9,10 Density functional theory (DFT) studies suggest that this carbon overlayer could have a graphene-like structure. 11,12 Other theoretical studies propose that C also interacts predominantly with subsurface Co sites leading to the formation of a carbide-like surface. 13 Besides, it has been shown that carbon atoms induce a structure rearrangement of the Co surface 4,5 similar to the (111) to (100) surface transformation seen on Ni. 14 In spite of these numerous studies, there is still a need to better quantify the stability domains of carbon species on the possible exposed sites of Co particles at the FT reaction conditions: T, P CO /P H 2 , P H 2 O , and also the Anderson−Schulz− Flory (ASF) distribution of products, α, which describes the relative ra...

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