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Despite progress in theoretical tools, the influence of solvation in heterogeneous catalysis remains poorly understood and predicted due to the large computational burden. In this work, we show that the inclusion of the solvation by water using a continuum model thermodynamically inhibits the O-H bond scissions involved in the ethanol aqueous phase reforming reaction over Pt(111), while it tends to favor the C-H, C-C, and C-O scissions. Then, we present a novel group additivity scheme for the free energy of adsorbates at the Pt/water interface that is able to capture this solvent effect. The mean absolute error (MeanAE) for the Gibbs free energy of formation is 3.3 kcal/mol over the investigated set of 200 species at the interface and the MeanAE for the 151 reaction free energies of ethanol aqueous phase reforming is 2.8 kcal/mol. Regarding the effect of solvation, our scheme is able to predict it with a MeanAE of about 1 kcal/mol. Together, the scheme promises to be accurate enough for narrowing down the most important reaction pathways in complex reaction networks as encountered in biomass conversion.

We re-investigate the image charge model of Iori and Corni (Iori and Corni, J. Comput. Chem. 2008, 29, 1656). We find that a simple symmetrization of their model allows to obtain quantitatively correct results for the electrostatic interaction of a water molecule with a metallic surface. This symmetrization reduces the magnitude of the electrostatic interaction to less than 10% of the total interaction energy. © 2017 Wiley Periodicals, Inc.

The accurate description of the energy of adsorbate layers is crucial for the understanding of chemistry at interfaces. For heterogeneous catalysis, not only the interaction of the adsorbate with the surface but also the adsorbate-adsorbate lateral interactions significantly affect the activation energies of reactions. Modeling the interactions of the adsorbates with the catalyst surface and with each other can be efficiently achieved in the cluster expansion Hamiltonian formalism, which has recently been implemented in a graph-theoretical kinetic Monte Carlo (kMC) scheme to describe multi-dentate species. Automating the development of the cluster expansion Hamiltonians for catalytic systems is challenging and requires the mapping of adsorbate configurations for extended adsorbates onto a graphical lattice. The current work adopts machine learning methods to reach this goal. Clusters are automatically detected based on formalized, but intuitive chemical concepts. The corresponding energy coefficients for the cluster expansion are calculated by an inversion scheme. The potential of this method is demonstrated for the example of ethylene adsorption on Pd(111), for which we propose several expansions, depending on the graphical lattice. It turns out that for this system, the best description is obtained as a combination of single molecule patterns and a few coupling terms accounting for lateral interactions.

A theoretical analysis was carried out on the mechanism of methane oxidation to methanol occurring on single site palladium oxide species [PdO]2+ supported on a model of Al-MCM-41 silica. Both 6- and 8-membered ring structures were considered to represent the support. The energy profile for each elementary reaction was determined from density functional theory calculations with the OPBE functional. The calculated overall activation energies are close to the experimental values. Our calculations confirm that spin inversion can play a significant role in decreasing the barrier heights for the pathways. Indeed, in this type of reactions we could show a crossing between singlet and triplet reaction paths. We showed that the mechanism for the C-H bond cleavage and for the formation of methanol has a radical nature. According to our results, the [PdO]2+ species located on a 8-membered ring of silica is more active than that deposited on a 6-membered ring. The calculated activation energies to cleave the methane C-H bond are 35 and 84 kJ/mol for the radical and ionic pathways, respectively. The activation barrier and the transition state geometry of this H-abstraction step are directly correlated with the optimal angle at which the substrate should approach the [Pd═O]2+ moiety, with the elongation of the Pd-Ooxo bond and finally with the energy of the π* acceptor orbital.

Identifying active catalysts for the conversion of alcohols into aldehydes or ketones and molecular hydrogen is highly desirable. Here the authors develop and validate against experiments a screening model based on DFT calculations and scaling relationships for identifying alcohol dehydrogenation catalysts.

The electrochemical hydrogenation (e‐hydrogenation) of unsaturated compounds like imines or carbonyls presents a benign reduction method. It enables direct use of electrons as reducing agent, water as proton source, while bypassing the need for elevated temperatures or pressures. In this contribution, we discuss the active species in electrocatalytic reductive amination with the transformation of acetone and methylamine as model reaction. Surprisingly, lead impurities in the ppm‐range proved to possess a significant effect in e‐hydrogenation. Accordingly, the influence of applied potential and cathode material in presence of 1 ppm Pb was investigated. Finally, we transferred the insights to the reduction of acetone manifesting comparable observations as for imine reduction. The results suggest that previous studies on electrochemical reduction in the presence of lead electrodes should be re‐evaluated. [ABSTRACT FROM AUTHOR]

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Abstract Background Irreparable rotator cuff tears are common and difficult to treat. Techniques for “filling the loss of substance” require fixation to the rotator cuff stump (tendon augmentation) or to the glenoid (superior capsular reconstruction), which are complicated by the narrow working zone of the subacromial space. The main objective of this study was to determine whether a braided graft of gracilis (GR) and semitendinosus (ST) could fill a loss of tendon substance from an irreparable rupture of the supra- and infraspinatus, by fixing the graft to the greater tuberosity and the spine of the scapula. Methods This was a cadaveric study with the use of ten specimens. The GRA and ST tendons were harvested, braided and reinforced with suture. An experimental tear of the supraspinatus (SS) and upper infraspinatus (IS) retracted at the glenoid was made. The GRAST transplant was positioned over the tear. The transplant was attached to the greater tuberosity by two anchors and then attached to the medial third of the scapular spine by trans-osseous stitching. The percentage of filling obtained was then measured and passive mobility of the shoulder was assessed. We proceeded to the same technique under arthroscopy for a 73 years old patient whom we treated for a painful shoulder with irreparable cuff tear. We inserted a GRAST graft using arthroscopy. Results The Braided-GRAST allowed a 100% filling of the loss of tendon substance. Mobility was complete in all cases. Conclusion This technique simplifies the medial fixation and restores the musculo-tendinous chain where current grafting techniques only fill a tendinous defect. The transplant could have a subacromial “spacer” effect and lower the humeral head. The donor site morbidity and the fate of the transplant in-vivo are two limits to be discussed. This anatomical study paves the way for clinical experimentation.

Graphitic carbon nitrides form a popular family of materials, particularly as photoharvesters in photocatalytic water splitting cells.

Experiments on model surfaces commonly help in identifying the structural sensitivity of catalytic reactions. Nevertheless, their conclusions do not frequently lead to devising superior "real-world" catalysts. For instance, this is true for single-crystal platinum electrodes and the oxygen reduction reaction (ORR), an important reaction for sustainable energy conversion. Pt(111) is substantially enhanced by steps, reaching a maximum at short terrace lengths of 3-4 atoms. Conversely, regular platinum nanoparticles with similar undercoordinated defects are less active than Pt(111) and their activity increases alongside the terrace-to-defect ratio. We show here that a model to design ORR active sites on extended surfaces can also be used to solve this apparent contradiction and provide accurate design rules for nanoparticles. Essentially, only surfaces and nanostructures with concave defects can surpass the activity of Pt(111), whereas convex defects are inactive. Importantly, only the latter are present in regular nanoparticles, which is why we design various concave nanoparticles with high activities.

The evaluation of solvation energies is a great challenge. We focus here on an organic molecule chemisorbed at a metal-liquid interface, as a prototypical system, essential in tribology, electrochemistry and heterogeneous catalysis. We compare an established implicit solvation scheme with a strategy based on molecular mechanics (MM) free energy perturbation (FEP) seeded by QM computations. First, we benchmark the approaches against experimental hydration energies of standard (organic) molecules and find acceptable errors in the order of 0.06 eV (1.3 kcal mol-1). Then, the impact of various parameters on the solvation energy of an adsorbate have been assessed on a typical system of interest, levulinic acid adsorbed at a Ru(0001)/water interface. We identify the need for dipole corrections or symmetric slabs when including solvation effects on metallic surfaces. The MM-FEP scheme is revealed to be as reliable as the implicit solvent for water. In the case of levulinic acid, both PCM and MM-FEP agree that the bulk solvation effect is not sufficient to change the adsorption mode from bidentate to mono-dentate, despite the fact that the COOH group is desolvated in the bidentate case. MM-FEP has the great advantage of being more easily generalized to other solvents and to be further improved which will be particularly useful to study solvent and (counter-)ion effects on interfacial reactions.

Solvation can substantially modify the adsorption properties of heterogeneous catalysts. Although essential for achieving realistic theoretical models, assessing such solvent effects over nanoparticles is challenging from a computational standpoint due to the complexity of those liquid/metal interfaces. This effect is investigated by ab initio molecular dynamics simulations at 350 K of a large platinum nanoparticle immersed in liquid water. The first solvation layer contains twice as much physisorbed water molecules above the terraces, than chemisorbed ones located only at edges and corners. The solvent stabilizes the binding energy of chemisorbates: 66% of the total gain comes from interactions with physisorbed molecules and 34% from the influence of bulk liquid.

The sluggish electrochemical kinetics of sulfur species remains a major hurdle for the broad adoption of lithium-sulfur batteries. Here, the authors construct an energy diagram of sulfur species to unveil their reaction pathways and propose a general strategy to accelerate electrochemical reactions.

Minimally invasive double-level osteotomy (DLP) surgery is performed in severe knee varus, when extra-articular deformity is identified in both the distal femur and proximal tibia. The main advantage is to maintain a horizontal joint line and avoid creating secondary anatomic deformities. This article considers the pearls and pitfalls in performing minimally invasive DLO surgery.