Finely divided nickel is one of the main heterogeneous catalysts for liquid phase hydrogenation of nitro and alkyne moieties. However, it constitutes a major safety hazard due to its pyrophoric...

The formation of iron phosphide nanoparticles (Fe x P NPs) is a well-studied process. It usually uses air-sensitive phosphorus precursors such as n-trioctylphosphine or white phosphorus. In this study, we report the synthesis and characterization of a remarkably stable tetrakis(acyl)cyclotetraphosphane, P 4 (MesCO) 4. We demonstrate that this compound can be used as a stoichiometric source of P(0) species in order to synthesize FeP and Fe 2 P nanoparticles at only 250 °C. This tunable process provides a route to monodisperse nanoparticles with different compositions and crystallinities. We combine X-Ray photoelectron spectroscopy (XPS) and atomic pair distribution function (PDF) in order to study the local order and bonding in the amorphous and crystalline materials. We show that crystalline FeP forms via an intermediate amorphous phase (obtained at a lower temperature) that presents local order similar to that of the crystalline sample. From the results of this work, a better understanding of the mechanism of the formation of amorphous and crystalline Fe x P NPs is provided which relies on the use of a stoichiometric and single P-source. We then explore the electrocatalytic properties of Fe x P nanoparticles for the hydrogen evolution reaction (HER) in acidic and neutral electrolytes. In both electrolytes, amorphous FeP is a more efficient catalyst than crystalline FeP, itself more efficient than crystalline Fe 2 P. Our study paves the way for a more systematic investigation of amorphous metal phosphide phases in electrocatalysis. It also shows the beneficial properties of PDF on the characterization of such nanomaterials, which is highly challenging.

A comprehensive molecular analysis of a simple aqueous complexing system—U(VI) acetate—selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.

No abstract

Molybdenum accepts oxidation states from -II to +VI. This versatility is highly beneficial for applications in catalysis, especially combined with sulfur to form the ubiquitous MoS 2 material. X-ray Absorption Near Edge Spectroscopy (XANES) is a particularly welladapted technique to study simultaneously both elements, since the K-edge of S (2472 eV) and the L 2,3 -edges of Mo (2520 -2625 eV) have similar absorption energies. It provides information on both the electronic and local structure of metal-containing species and allows drawing structure-activity relationships. However, L 2,3 -edges are difficult to interpret, especially for 4d and 5d transition metals. In addition, only few recent studies focus on the measurement of the signal of Mo-based reference compounds, meaning that the references from the literature do not benefit from recent technical progress. Notwithstanding theoretical tools that allow a deep understanding of such spectroscopic data, the lack of reference spectra prevents a quick yet reliable interpretation. In this work, we provide a method for the interpretation of X-ray absorption near edge structure (XANES) data at the Mo L 2,3 -edges, based on a library of spectra of simple Mo compounds. From our analysis, we suggest using the L 3 -edge to determine the oxidation state (in selected cases) and the L 2 -edge to gain insight on geometry around the Mo atoms. This method is then applied to a series of molybdenum sulfides compounds in order to rationalize their structures. Besides this example, these guidelines should help to qualitatively interpret XANES of Mo at L 2,3 -edges in future studies.

Transition metal carbides (TMCs) have attracted great interest due to their mechanical and catalytic properties but their syntheses generally require energy-consuming processes with temperatures above 800 °C. We report here...

Hydrosilylation reactions are commonly used for the reduction of carbonyl bonds in fine chemistry, catalyzed by transition metal complexes. The current challenge is to expand the scope of metal-free alternative catalysts, including in particular organocatalysts. This work describes the organocatalyzed hydrosilylation of benzaldehyde with a phosphine, introduced at 10 mol%, and phenylsilane at room temperature. The activation of phenylsilane was highly dependent on the physical properties of the solvent such as the polarity, and the highest conversions were obtained in acetonitrile and propylene carbonate with yields of 46 % and 97 %, respectively. The best results of the screening over 13 phosphines and phosphites were obtained with linear trialkylphoshines (PMe 3 , P n Bu 3 , POct 3 ), indicating the importance of their nucleophilicity, with yields of 88 %, 46 % and 56 %, respectively. With the help of heteronuclear 1 HÀ 29 Si NMR spectroscopy, the products of the hydrosilylation (PhSiH 3-n (OBn) n ) were identified, allowing a monitoring of the concentration in the different species, and thereby of their reactivity. The reaction displayed an induction period of ca. 60 min, followed by the sequential hydrosilylations presenting various reaction rates. In agreement with the formation of partial charges in the intermediate state, we propose a mechanism based on a hypervalent silicon center via the Lewis base activation of the silicon Lewis acid.

Neuromuscular diseases are genetic conditions which result in a progressive loss of muscle function. One of the hallmarks is the replacement of muscle by fat tissue which can be quantified using Magnetic Resonance Imaging (qMRI). Although individual muscles are generally affected by this replacement, the corresponding degree of fat infiltration differs from one muscle to another so that Fat Fraction quantification in individual muscles is of importance and this requires a delineation procedure to be performed. Given that the manual delineation is tedious and time consuming, semi-automatic and automatic approaches have been developed over the last decade. More specifically, deep learning approaches have provided promising results for automatic segmentation of medical images and U-Net has been the most largely used Convolutional Neural Network. A modified version of U-Net incorporating an "attention" block (Attention U-Net) has been proposed recently. It has been initially used for the automatic delineation of Pancreas on CT images. In the present work, we intended to compare the performance of 2D U-Net and 2D Attention U-Net for i) the segmentation of individual thigh muscles on MR images from neuropathic patients and controls and ii) the quantification of FF. Our results illustrate that both Attention U-Net and U-Net provide very high Dice scores with a significantly higher value for Attention U-Net (90% to 94.4%) in comparison with U-Net (86% to 94.2%). Nevertheless, a statistical analysis shows that the FF estimation is not significantly impacted by the deviation of the Dice score between the networks. This statistical analysis also shows that Attention U-Net and U-Net allow to estimate a fat fraction comparable with those computed by using the segmentation mask performed by experts.