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ChemCatChem homepage for more articles in the collection. The mechanism of the low‐temperature water gas shift reaction (LTWGS) on an Au/CeO2 catalyst was investigated by means of in situ diffuse reflectance infrared (DRIFT) spectroscopy. Under steady‐state LTWGS reaction (373–623 K), the catalyst is partially reduced, and signals from carbonate/formate dominates the infrared spectra. Time‐resolved pulse of CO experiment under a constant partial pressure of water at 423 K indicates that Ce4+ can be reduced to Ce3+ and that formate (HCOO) species cannot be directly related to the CO2 production. Further information was obtained by performing modulation excitation spectroscopy (MES) experiments coupled with a phase‐sensitive detection (PSD) method. Under periodic modulation of the CO partial pressure while keeping the H2O concentration constant, most of the intense bands of carbonate and formate remained constant, indicating that these species are only spectators. The same is observed for the concentration of Ce3+. Conversely, signals in‐phase with the conversion of CO to CO2 are observed and assigned to carboxyl [C(O)OH] and carboxylate (CO2δ−) species, while some monodentate formate (m‐HCOO) also changes but at a lower rate. A plausible associative reaction mechanism where carboxyl/carboxylate are key intermediates is postulated. [ABSTRACT FROM AUTHOR]

In this special issue different strategies in theory and experiments are exposed to understand and explain the physicalchemistry behind Catalysis and Surface Science. [ABSTRACT FROM AUTHOR]

Abstract: Doping CeO2 with gallium leads to promising materials with application in hydrogen purification processes for fuel cells. The bulk ceria–gallia is investigated by ab initio calculations. The outstanding reactivity is explained by important relaxations induced by gallium in the ceria host, having a strong impact in the electronic structure. As a result, the mixed oxide is found to be more reducible than the pure oxides in agreement with experimental data. It is thus possible to correlate structure and reactivity of the doped system on the molecular level, representing a step forward to the rational design of materials with selected properties. [Copyright &y& Elsevier]

Abstract: The hydrogen oxidation reaction (hor) was studied in steady state conditions on a palladium thin film electrode supported on a gold rotating disc. The electrode surface was characterized by cyclic voltammetry and SEM observation. The hydrogen absorption process was analysed by open circuit potential decay in an acid solution saturated with hydrogen and the kinetic measurements were carried out potentiostatically in the same solution. The results obtained show a marked change on the dependence of the current density on overpotential due to the transition between the α and β phases of the Pd–H system. These results were correlated with appropriate kinetic expressions and the corresponding electrocatalytic activity of both phases was estimated. [Copyright &y& Elsevier]

The deposition of zinc from aqueous solutions is of great practical importance, and it also serves as a prototype for the deposition of divalent ions. Both experiment and theory agree, that it takes place in two steps. Previous theoretical work [1] had suggested that the step, Zn + + + e - → Zn + takes place in the outer sphere, but gave a prohibitively high energy of activation of the order of 1.4 eV, in accord with the enigma of metal deposition postulated by Gileadi [2]. In this work the treatment of the reactant – solvent interaction is substantially improved by introducing nonlinear terms based on molecular dynamics. Our calculations suggest that the first steps follows an inner sphere path with a much lower energy of activation, which results in a physically adsorbed Zn + ion. The second step then occurs on the electrode surface. These findings are in line with experimental data. [ABSTRACT FROM AUTHOR]

The adsorption of toluene on cerium oxide was investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations. It is shown that the toluene molecule undergoes dissociative adsorption with the loss of a hydrogen atom from the methyl group and the generation of both, a benzyl (C6H5–CH2−) and a surface hydroxyl species. Characteristic infrared signals are observed due to the formation of a methylene group at 2800 cm−1 (ν CH2) and 1300 cm−1 (δ CH2). All vibrational modes were identified combining DFT calculations of the optimized system and experimental evidences. An adsorbed stable benzyl structure was identified with a binding energy of about − 0.65 eV, which supports the experimental findings. Temperature programmed surface reaction followed by DRIFTS and mass spectrometry showed that benzyl species are oxidized by lattice oxygen to benzoate, formate and, finally, to CO and CO2. Understanding the reactivity of ceria surfaces is key to improve the performance of combustion catalysts for volatile organic compounds abatement. [ABSTRACT FROM AUTHOR]

On many metals, small quantities of chloride are known to be adsorbed at potentials well below the potential of zero charge and to influence other electrochemical processes. In order to understand this behavior, we have investigated the adsorption of a single Cl− ion from aqueous solution by a combination of density functional theory and classical molecular dynamics, taking Au(111) as a model surface. While in the vacuum, Cl is adsorbed directly on the surface in the 3-fold hollow sites, whereas in aqueous solution, the optimal position lies a fraction of an Ångstrom towards the solution, where the ion is almost fully solvated and mobile in the direction parallel to the surface. As a result, the adsorption of a single ion is exothermic by about −0.6 eV, even at the potential of zero charge. This adsorption behavior is limited to low coverages because the adsorbates repel each other and because full solvation shells can only form at low coverage. Unlabelled Image • Cl− is adsorbed with an energy of −0.6 V at the pzc of Au(111). • It adsorbs at a distance of 0.8 Å from the surface and is strongly solvated. • It is highly mobile in the direction parallel to the surface. • This picture is valid only at low coverage. [ABSTRACT FROM AUTHOR]

It is assumed that genetic diseases affecting the metabolism of cysteine and the kidney function lead to two different kinds of pathologies, namely cystinuria and cystinosis whereby generate l-cystine crystals. Recently, the presence of l-cysteine crystal has been underlined in the case of cystinosis. Interestingly, it can be strikingly seen that cystine ([–S–CH2–CH–(NH2)–COOH]2) consists of two cysteine (C3H7NO2S) molecules connected by a disulfide (S–S) bond. Therefore, the study of cystine and cysteine is important for providing a better understanding of cystinuria and cystinosis. In this paper, we elucidate the discrepancy between l-cystine and l-cysteine by investigating the theoretical and experimental infrared spectra (IR), X-ray diffraction (XRD) as well as Raman spectra aiming to obtain a better characterization of abnormal deposits related to these two genetic pathologies. [ABSTRACT FROM AUTHOR]

The reactivity and structure of several platinum nanoparticles adsorbed on a (5,5) CNT have been studied on the basis of DFT. Changes in the materials reactivity due to charge redistribution and chemical and geometrical factors were observed. Additionally, we have investigated the nanoparticles reactivity for water dissociation and found a competing behavior between the particle structure and charge accumulation, which influences the decrease in the activation energies of the process and provides a deeper understanding of the reaction path and the material behavior as well. [ABSTRACT FROM AUTHOR]

[Display omitted] • Study of alkali ions approaching an electrode surface. • The energetics follow the Hofmeister series. • Li+ and Na+ show signs of structure making. • K+ and Cs+ shows signs of structure breaking. The approach of alkali ions from an aqueous solution towards a gold electrode has been studied by biased molecular dynamics. In accord with the Hofmeister series, Li+ and Na+ show signs of structure making, K+ and Cs+ of structure breaking. For all ions the potential of mean force at first rises, when the ion approaches the surface, passes through a maximum and then drops again to a local minimum. For the structure breaking ions Cs+ and K+ the solvation energies in the minima are the same as in the bulk, for Na+ and Li+ they are a little higher. [ABSTRACT FROM AUTHOR]

Geheimnis gelüftet: Die Abscheidung von Silber ist eine der schnellsten elektrochemischen Reaktionen, obwohl das Ag+ ‐ Ion beim Einbau in die Elektrode über 5 eV Solvatisierungsenergie verliert. Das Phänomen, das ein Beispiel für das „Enigma der Metallabscheidung“ ist, wurde mit einer Kombination von MD ‐ Simulationen, DFT und einer eigens entwickelten Theorie untersucht. Das Ag+ ‐ Ion erfährt an der Oberfläche eine starke Wechselwirkung mit dem sp ‐ Band von Silber, welche die Reaktion katalysiert. [ABSTRACT FROM AUTHOR]

Abstract: Cyanide-modified Pt(111) surfaces have been recently used to study atomic-ensemble effects in electrocatalysis. These studies have been based on the assumption that cyanide acts as a third body, blocking some surface sites but leaving the electronic properties of the surrounding ones unaltered, although this is in apparent contradiction with the observation of a positive shift of 0.2V in the onset of hydrogen adsorption on cyanide-modified Pt(111) electrodes, as compared with clean Pt(111). We have performed theoretical calculations in order to provide support to this assumption and explain the positive shift in the onset of hydrogen adsorption, which is shown to be due to the formation of CNHad. [Copyright &y& Elsevier]

A perfect match: Silver deposition is one of the fastest electrochemical reactions, even though the Ag+ ion loses more than 5 eV solvation energy in the process. This phenomenon, an example of the enigma of metal deposition, was investigated by a combination of MD simulations, DFT, and specially developed theory. At the surface, the Ag+ ion experiences a strong interaction with the sp band of silver, which catalyzes the reaction. [ABSTRACT FROM AUTHOR]

The hydrogenation reaction of acetonitrile adsorbed on a platinum surface to produce amines has been investigated by theoretical and in situ infrared studies. An energetic, kinetics and vibrational analysis have been performed to unravel the elementary steps of the reaction and to clarify the mechanism. The comparison with the experiments allows us to identify an imine as a crucial intermediate for this reaction. [ABSTRACT FROM AUTHOR]

Abstract The adsorption of OH on Ni(111) has been investigated by a combination of density functional theory and classical molecular dynamics. At low coverage, the adsorption is strong, the adsorbate carries almost unit negative charge, and interacts strongly with water. Because of their high charges, adsorbed OH species repel each other, and adsorption becomes less favorable with increasing coverage. Adsorption on Ni(111) is contrasted with that on Pt(111). Highlights • OH is strongly adsorbed at the hollow sites on Ni(111). • The adsorbed OH carries almost unit negative charge. • Adsorption becomes less favorable with increasing coverage. [ABSTRACT FROM AUTHOR]

Abstract Normally ions with the same charge repel each other, but in very rare cases an intervening medium can produce an apparent attraction. We have studied the adsorption of Li-ions on semiconducting carbon nanotubes by density functional theory, one ion being inside, the other outside. The tube shields the direct Coulomb interaction between the ions, but the presence of the ion inside facilitates the adsorption of the ion outside, thus producing an apparent attraction. We give a quantitative explanation based on the electronic band structure of the tube, and surmise, that the same effect will hold on other carbon materials. Our results may explain the apparent attraction of Li-ions that has been observed in Li-batteries. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

A detailed analysis of fluorinated polyphenylthiols adsorbed on a nanostructured Au(1 1 1) is performed on the basis of first principle calculations to understand the interface at the atomic level. Our analysis is focused on the energetics, the density of states projected onto different atoms, the charge rearrangements induced by the presence of the adlayer as well as the modifications in the electrostatic potential to gain a deeper insight into the involved processes. [ABSTRACT FROM AUTHOR]

Abstract: The vibrational signatures of the calcium oxalate polyhydrates are investigated using a combination of Density Functional Theory‐Dispersion corrected, Fourier Transform‐ Raman and ‐Infrared (IR) spectroscopies. Most vibrational bands were assigned and the theoretical predictions were compared with in‐house and other experimental data, for both, IR and Raman spectroscopies. Such an approach allowed a more accurate analysis of vibrational spectra helping in the completion of the band assignments of the vibrational bands of the mono, di, and tri hydrate calcium oxalate (COM, COD, and COT). Particular attention has been paid to the degree of hydration of COD, the low Raman wavenumbers, and the presence of oxalic acid in natural calcium oxalate polyhydrates. The obtained results are expected to be supportive in the detection of the different polyhydrates in natural samples, such as in kidney stones. [ABSTRACT FROM AUTHOR]

The behavior of a calixarene derivative – p–tert butyl calix[4]arene (TBC4) – as receptor for transition metals (Cr, Ni, Cd) has been investigated by density functional calculations. Particular attention has been paid to the energetics and the nature of the metal–TBC4 interactions. Our results predict, that TBC4 should be a good receptor for the extraction of Ni, due to the strong interactions between Ni and the cone-shaped part of the organic molecule in comparison with Cd and Cr. [Display omitted] • TBC4 can be used as metal receptor. • TBC4 shows strong interaction with Ni. • TBC4 shows no interaction with Cd. • TBC4 is predicted to be an efficient receptor for Ni. [ABSTRACT FROM AUTHOR]

We examine the insertion of alkali and halide ions into narrow nanotubes of graphite and gold by density functional theory (DFT). For tubes with diameters less than about 10 Åthe optimum position of the ion is in the center of the tube. Bader analysis and an analysis of the densities of states gave contradictory results for the charge on the halide ions, but we argue on physical grounds that they carry unit negative charge. We have calculated the energies of inserting the atoms into the tubes, where they are ionized. Because of the small system size the work function of the tubes changes during this process, which makes it difficult to interpret these energies. The surrounding tubes screen the ionic charge very effectively; thereby the ion-ion interactions are strongly reduced, which explains, why narrow tubes store charge more effectively than wider one. These effects are stronger for gold than for graphite tubes. We define an effective image radius of a cylindrical tube, and calculate the image energy experienced by the ions. [ABSTRACT FROM AUTHOR]

Abstract: We examine the insertion of alkali ions into narrow nanotubes of graphite and gold by density functional theory. The surrounding tubes screen the ionic charge very effectively; the resulting image energy compensates well for the loss of solvation. In addition, ion–ion interactions are strongly reduced. These effects are stronger for gold than for graphite tubes. Our results explain at an atomic level, why narrow tubes store charge so effectively. [Copyright &y& Elsevier]