Search

A screening study of the catalytic performance of ternary alloy nanoparticles containing nickel, iron and gallium supported on silica for methanol synthesis from CO2 and H2 was performed. Catalysts were prepared by incipient wetness impregnation and subsequently reduced in H2 before catalytic testing. Ni2FeGa showed the best performance of the tested catalysts in terms of methanol yield. An optimization of the preparation was done to improve activity and selectivity, reaching a performance close to that of commercially available Cu/ZnO/Al2O3/MgO at low reaction temperatures and pressure. Extensive in situ characterisation using environmental TEM, in situ XRD and in situ EXAFS of the formation of the Ni2FeGa catalyst explains an optimal reduction temperature of 550 °C: warm enough that the three atomic species will form an alloy while cold enough to prevent the catalyst from sintering during the formation. [ABSTRACT FROM AUTHOR]

The recently emerged actinide (An) M 4,5 -edge high-energy resolution X-ray absorption near-edge structure (HR-XANES) technique has proven to be very powerful for oxidation state studies of actinides. In this work, for the first time, Np M 5 -edge HR-XANES was applied to study Np sorption on illite. By improving the experimental conditions, notably by operation of the spectrometer under He atmosphere, it was possible to measure Np M 5 -edge HR-XANES spectra of a sample with ≈ 1 μg Np/g illite (1 ppm). This is 30-2000 times lower than Np loadings on mineral surfaces usually investigated by X-ray absorption spectroscopy. A newly designed cryogenic configuration enabled sample temperatures of 141.2 ± 1.5 K and successfully prevented beam-induced changes of the Np oxidation state. The described approach paves the way for the examination of coupled redox/solid-liquid interface reactions of actinide ions via An M 4,5 -edge HR-XANES spectroscopy at low metal ion concentrations, which are of specific relevance for contaminated sites and nuclear waste disposal studies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

The combination of wet-chemistry experiments (measurements of pH, E h , and [Tc]) and advanced spectroscopic techniques (K- and L 3 -edge X-ray absorption fine structure spectroscopy) confirms the formation of a very stable Tc(V)-gluconate complex under anoxic conditions. In the presence of gluconate and an excess of Sn(II) (at pe + pH ≈ 2), technetium forms a very stable Tc(IV)-gluconate complex significantly enhancing the solubility defined by TcO 2 (s) in hyperalkaline gluconate-free systems. A new setup for "tender" X-ray spectroscopy (spectral range, ∼2-5 keV) in transmission or total fluorescence yield detection mode based on a He flow cell has been developed at the INE Beamline for radionuclide science (KIT light source). This setup allows handling of radioactive specimens with total activities up to one million times the exemption limit. For the first time, Tc L 3 -edge measurements (∼2.677 keV) of Tc species in liquid (aqueous) media are reported, clearly outperforming conventional K-edge spectroscopy as a tool to differentiate Tc oxidation states and coordination environments. The coupling of L 3 -edge X-ray absorption near-edge spectroscopy measurements and relativistic multireference ab initio methods opens new perspectives in the definition of chemical and thermodynamic models for systems of relevance in the context of nuclear waste disposal, environmental, and pharmaceutical applications.