A kinetic model of water adsorption, clustering and dissociation on the Fe3S4{001} surface

The interaction of water with catalyst surfaces is a common process which requires investigation. Here, we have employed density functional theory calculations to investigate the adsorption of up to ten water molecules on the {001} surface of greigite (Fe3S4), which owing to its redox properties, is of increasing interest as a catalyst, e.g. in electro-catalysis. We have systematically analyzed and characterized the modes of water adsorption on the surface, where we have considered both molecular and dissociative adsorption processes. The calculations show that molecular adsorption is the predominant state on these surfaces, from both a thermodynamic and kinetic point of view. We have explored the molecular dispersion on the surface under different coverages and found that the orientation of the molecule, and therefore the surface dipole, depends on the number of adsorbed molecules. The interactions between the water molecules become stronger with an increasing number of water molecules, following an exponential decay which tends to the interaction energy found in bulk water. We have also shown the evolution of the infra-red signals as a function of water coverage relating to the H-bond networks formed on the surface. Next we have included these results in a classical micro-kinetic model, which introduced the effects of temperature in the simulations, thus helping us to derive the water cluster size on the greigite surface as a function of the initial conditions of pressure, temperature and external potential. The kinetic model concluded that water molecules agglomerate in clusters instead of wetting the surface, which agrees with the low hydrophilicity of Fe3S4. Clusters consisting of four water molecules was shown to be the most stable cluster under a wide range of temperatures and external potential

Catalytic water dissociation by greigite Fe3S4surfaces: density functional theory study

The iron sulfide mineral greigite, Fe3S4, has shown promising capability as a hydrogenating catalyst, in particular in the reduction of carbon dioxide to produce small organic molecules under mild conditions. We employed density functional theory calculations to investigate the {001},{011} and {111} surfaces of this iron thiospinel material, as well as the production of hydrogen ad-atoms from the dissociation of water molecules on the surfaces. We systematically analysed the adsorption geometries and the electronic structure of both bare and hydroxylated surfaces. The sulfide surfaces presented a higher flexibility than the isomorphic oxide magnetite, Fe3O4, allowing perpendicular movement of the cations above or below the top atomic sulfur layer. We considered both molecular and dissociative water adsorption processes, and have shown that molecular adsorption is the predominant state on these surfaces from both a thermodynamic and kinetic point of view. We considered a second molecule of water which stabilizes the system mainly by H-bonds, although the dissociation process remains thermodynamically unfavourable. We noted, however, synergistic adsorption effects on the Fe3S4{001} owing to the presence of hydroxyl groups. We concluded that, in contrast to Fe3O4, molecular adsorption of water is clearly preferred on greigite surfaces

Selective hydrogenation of CO on Fe3S4{111}: a computational study

Fischer-Tropsch (FT) synthesis has been a recursive method to form valuable molecules from syngas. Metal surfaces have been extensively studied as a FT catalyst, among them, iron presented several phases under reaction conditions, oxide and carbides, as active sites for the FT and reverse water gas shift reaction. We present the CO reduction on an iron sulfide phase with spinel structure, Fe3S4, considering also the pathways where C-O dissociates leaving CHX species on the surface, which may feed longer aliphatic chains via FT process. We analysed the thermodynamic and kinetic availability of each step leading to O, OH species co-adsorbed on the surface as well as the formation of H2O from the hydrogenation of the alcohol group in the molecule. This detailed analysis let to energy profiles, on both active sites of the surface, and conclude that this Fe3S4 surface is high selectivity towards the formation of methanol, in full agreement with experimental results. These findings point out that the C-C bond formation on greigite takes place through an hydroxycarbene FT mechanism

DFT-D2 Study of the Adsorption and Dissociation of Water on Clean and Oxygen-Covered {001} and {011} Surfaces of Mackinawite (FeS)

We present a dispersion-corrected density functional theory study of the adsorption and dissociation reactions of oxygen and water on the {001} and {011} surfaces of mackinawite (FeS). A chemical picture of the initial steps of the mackinawite {001} and {011} surfaces oxidation process in the presence of oxygen and water is presented in the present investigation. Our results show that, while water interacts weakly with the Fe ions on both surfaces and only oxidizes them to some extent, atomic and molecular oxygen interact strongly with the FeS{011} surface cations by drawing significant charge from them, thereby oxidizing them from Fe2+ to Fe3+ formal oxidation state. We show from our calculated adsorption energies and activation energy barriers for the dissociation of H2O on the clean and oxygen-covered FeS surfaces, that preadsorbed oxygen could easily activate the O–H bond and facilitate the dissociation of H2O to ferric-hydroxy, Fe3+–OH– on FeS{011}, and to zerovalent sulfur-hydroxyl, S0–OH– on FeS{001}. With the aid of preadsorbed O atom, the activation energy barrier for dissociating hydrogen atom from H2O decreases from 1.73 to 1.19 eV on the FeS{001}, and from 0.83 to 0.14 eV on the FeS{011}. These findings provide molecular-level insight into the mechanisms of mackinawite oxidation, and are consistent with experimental results, which have shown that oxygen and water are necessary for the oxidation process of mackinawite and its possible transformation to pyrite via greigite

Наукові засади розвитку інституту юридичної риторики: в контексті теорії юридичної аргументації

Саме аргументація в юридичній риториці є одним із ключових компонентів, який позначається на результативності та якості юридичного дискурсу. Тому для наукового дослідження юридичної риторики як науким провідне значення має вивчення теорії юридичної аргументації, як складової загальної теорії аргументації.Именно аргументация в юридической риторике является одним из ключевых компонентов, который проявляет себя в результативности и качестве юридического дискур­са. Поэтому для научного исследования юридической риторики как науки приоритетное значение имеет изучение теории юридической аргументации, как составляющей общей теории аргументации.The argument in legal rhetoric is one of key components who prover in productivity and quality of a legal discourse. Therefore for scientific research of legal rhetoric science priority has studyind of the legal argument, as making general of the argument

Effect of strontium inclusion on the bioactivity of phosphate-based glasses

We have conducted first-principles and classical molecular dynamics simulations of various compositions of strontium-containing phosphate glasses, to understand how strontium incorporation will change the glasses’ activity when implanted into the body (bioactivity). To perform the classical simulations, we have developed a new interatomic potential, which takes account of the polarizability of the oxygen ions. The Sr-O bond length is ∼ 2.44 − 2.49Å, and the coordination number is 7.5 – 7.8. The Qn distribution and network connectivity were roughly constant for these compositions. Sr bonds to a similar number of phosphate chains as Ca does; based on our previous work [J. K. Christie et al., J. Phys. Chem. B 117, 10652 (2013)], this implies that SrO ↔ CaO substitution will barely change the dissolution rate of these glasses, and that the bioactivity will remain essentially constant. Strontium could therefore be incorporated into phosphate glass for biomedical applications

Теоретико-методологічні засади адаптивного інноваційного розвитку

Подано визначення змісту управління адаптивним інноваційним розвитком, заснованого на використанні його здібностей до трансформації з урахуванням особливостей зовнішнього та внутрішнього середовища суб’єкта сукупності дій, необхідних для здійснення впливу на процеси в усіх сферах управління, що забезпечує інноваційну, організаційно-управлінську, технічну, фінансову та кадрову стійкість. Ключові слова: інновації, інноваційний розвиток, адаптація, адаптивність, механізм, система, процес.Представлено определение содержания управления адаптивным инновационным развитием, основанным на использовании его способностей к трансформации с учетом особенностей внешней и внутренней среды субъекта совокупности действий, необходимых для осуществления влияния на процессы во всех областях управления, обеспечивающих инновационную, организационно-управленческую, техническую, финансовую и кадровую устойчивость. Ключевые слова: инновации, инновационное развитие, адаптация, адаптивность, механизм, система, процесс.The paper presents the definition of management of adaptive innovation-based development that is based on the use of its ability to transform in view of external and internal environment of the subject of actions necessary for making influence on the processes in all areas of management, providing innovative, organizational, administrative, technical, financial and personnel stability of the production company. Keywords: innovation, innovation-based development, adaptation, adaptability, mechanism, system, process

Configurational analysis of uranium-doped thorium dioxide

While thorium dioxide is already used industrially in high temperature applications, more insight is needed about the behaviour of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model, commensurate with a prominent existing UO2 potential, to conduct configurational analyses of uranium-doped ThO2 supercells. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analysed the distribution of low concentrations of uranium in the bulk material, but have not observed the formation of uranium clusters or a single dominant configuration