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In this study, we use zeolite Y as a support for the synthesis of Sn and Ga doped zeolites aimed at the isomerization of glucose to fructose. Though these materials are inactive in water, they are active in methanol and we could ascertain a reaction pathway involving a hydride shift for the interconversion of glucose to fructose and mannose, and a Brønsted acid pathway with the formation of a methyl fructoside intermediate and its hydrolysis to fructose if water was added afterwards. By using characterizations comprising: chemisorption, XPS, XRD, HAADF-STEM and EXAFS; it was possible to demonstrate that a straightforward impregnation protocol for the preparation of our catalysts, led to Sn/Y mainly consisting of small SnO2 clusters on the external surface of the zeolite, whereas Ga/Y consisting of highly dispersed Ga species mostly inside the zeolite pores; and a catalytic activity that appears to be dominated by Brønsted acid sites.

We report a systematic study of the $5d$-electron-doped system Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$ ($0 \leq x \leq 0.15$). With increasing $x$, the orthorhombic $b$~axis decreases slightly while accompanying changes in $a$ and $c$ leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor CeFe$_2$Al$_{10}$, the low-temperature energy gap which is proposed to be a consequence of strong $c \mhyphen f$ hybridization, is suppressed by a small amount of Ir substitution for Fe, and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at $x=$~0.04) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a N\'eel temperature, $T_{\mathrm{N}}$, of 3.1(2)~K for $x = 0.15$. The ordered moment is estimated to be smaller than 0.07(1)~$\mu_\mathrm{B}$/Ce although the trivalent state of Ce is confirmed by Ce L$_3$-edge x-ray absorption near edge spectroscopy. It is suggested that the $c \mhyphen f$ hybridization gap, which plays an important role in the unusually high ordering temperatures observed in Ce$T_2$Al$_{10}$ ($T$ = Ru and Os), may not be necessary for the onset of magnetic order with a low $T_{\mathrm{N}}$ seen here in Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$., Comment: 12 pages, 11 figures

A new CAD program, PolyCAD, designed for X-ray photon tracing in polycapillary optics is described. To understand the PolyCAD code and its results, the theoretical basis of X-ray transmission by a single cylindrical channel (monocapillary) is discussed first. Then the simplest cases of cylindrically and conically shaped polycapillary optics are examined. PolyCAD allows any type of X-ray source to be used: an X-ray tube of finite beam dimensions or an astrophysical object can be simulated in combination with the polycapillary optics. The radiation distribution images formed on a screen located at various focal distances are discussed. The good agreement of some of the PolyCAD results with those reported in earlier papers validate the code. This is the first paper of a series dedicated to the development of an exhaustive CAD program, work is in progress to develop the code to include other polycapillary-optics shapes, such as semi-lenses and full-lenses., Comment: Submitted to Applied Optics

A substantial improvement in the study of the physical and radiative characteristics of dust particles and in climate models has occurred in order to reliably predict their impact on climate. However, key properties of mineral particles are still little known so that global dust cycle simulations are still poor. Dust size distribution is a key issue together with particle morphology, mineralogical composition and optical characteristics. Mineralogy of dust is required for source identification. The geochemical and isotopic composition of mineral dust is also a useful tool for discriminating its geographic origin. However, the analysis of low concentration insoluble atmosphere dust depositions is a challenging research area because of the extremely small amount of material available in crystalline form

High-entropy oxides based on transition metals, such as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (TM-HEO), have recently drawn special attention as potential anodes in lithium-ion batteries due to high specific capacity and cycling reversibility. However, the lithiation/delithiation mechanism of such systems is still controversial and not clearly addressed. Here, we report on an operando XAS investigation into TM-HEO-based anodes for lithium-ion cells during the first lithiation/delithiation cycle. This material showed a high specific capacity exceeding 600 mAh g-1 at 0.1 C and Coulombic efficiency very close to unity. The combination of functional and advanced spectroscopic studies revealed complex charging mechanisms, developing through the reduction of transition-metal (TM) cations, which triggers the conversion reaction below 1.0 V. The conversion is irreversible and incomplete, leading to the final collapse of the HEO rock-salt structure. Other redox processes are therefore discussed and called to account for the observed cycling behavior of the TM-HEO-based anode. Despite the irreversible phenomena, the HEO cubic structure remains intact for ∼60% of lithiation capacity, so proving the beneficial role of the configuration entropy in enhancing the stability of the HEO rock-salt structure during the redox phenomena.

A series of MoOx-modified Fe2O3 catalysts have been prepared in an attempt to make core-shell oxidic materials of the type MoOx/Fe2O3. It is conclusively shown that for three monolayers of Mo dosed, the Mo stays in the surface region, even after annealing to high temperature. It is only when the material is annealed above 400 C that it reacts with the iron oxide. We show by a combination of methods, and especially by XAFS, that at temperatures above 400 C, most of the Mo converts to Fe2(MoO4)3, with Mo in a tetrahedral structure, whereas below that temperature, nanocrystalline MoO 3 is present in the sample; however, the active catalysts have an octahedral MoOx layer at the surface even after calcination to 600 C. This surface layer appears to be present at all temperatures between 300 and 600 C, and it is the nanoparticles of MoO3 that are present at the lower temperature that react to form ferric molybdate, which underlies this surface layer. It is the MoOx layer on the Fe2(MoO 4)3 underlayer that makes the surface active and selective for formaldehyde synthesis, whereas the iron oxide surface itself is a combustor. The material is both activated and improved in selectivity due to the dominance of the methoxy species on the Mo-doped material, as opposed to the much more stable formate, which is the main intermediate on Fe2O 3. © 2013 American Chemical Society.

The possibility of finding a stratigraphically intact ice sequence with a potential basal age exceeding one million years in Antarctica is giving renewed interest to deep ice coring operations. But the older and deeper the ice, the more impactful are the post-depositional processes that alter and modify the information entrapped within ice layers. Understanding in situ post-depositional processes occurring in the deeper part of ice cores is essential to comprehend how the climatic signals are preserved in deep ice, and consequently how to construct the paleoclimatic records. New techniques and new interpretative tools are required for these purposes. In this respect, the application of synchrotron light to microgram-sized atmospheric dust samples extracted from deep ice cores is extremely promising. We present here preliminary results on two sets of samples retrieved from the Talos Dome Antarctic ice core. A first set is composed by samples from the stratigraphically intact upper part of the core, the second by samples retrieved from the deeper part of the core that is still undated. Two techniques based on synchrotron light allowed us to characterize the dust samples, showing that mineral particles entrapped in the deepest ice layers display altered elemental composition and anomalies concerning iron geochemistry, besides being affected by inter-particle aggregation.

Angle-resolved XANES spectra have been collected at the potassium K edge using polarized synchrotron radiation on several natural mica crystals. Experimental data have been interpreted on the basis of the MS theory and, within this theoretical framework, the edge of this low-Z atom is decomposed so as to produce two partial patterns giving, respectively, the full in-plane absorption spectrum and the full out-of-plane one. The method here described is appropriate to describe the X-ray dichroic behaviour of solid layered compounds and/or two-dimensionally extended structures.

The X-ray absorption angle-dependent behavior at the potassium K -edge has been determined for two end-members and two intermediate trioctahedral micas, which are representative of the Fe2+Mg−1, Fe3+Al−1, SiAl−1FeLi−1, and F−1OH exchange vectors, using horizontally polarized synchrotron radiation. Experimental spectra are interpreted by the multiple scattering theory following decomposition according to the angular dependence approach of Brouder (1990). The experimental spectra sum up anisotropic effects deriving from in-plane and out-of-plane photoelectron interactions with the potassium near- and next-near neighbors up to the fifth/sixth coordination sphere. For the first time, the absorption edge of a low Z atom is decomposed so as to produce two partial patterns giving, respectively, the full in-plane absorption spectrum (σ||) and the full out-of-plane spectrum (σ⊥). They fully describe the complete X-ray absorption dichroic behavior of layered compounds, of which mica is a prototype. σ|| essentially reflects the arrangement of the atoms located in the mica interlayer space and facing tetrahedral sheets. Differences among the four micas depend on structural changes induced by the adaptation of their tetrahedral sheets to the increasing sizes of their octahedral sheet due to chemical substitutions (i.e., the Fe2+Mg−1 vector, mainly) and to chemical changes at the octahedral anion site (F−1OH vector). By contrast, σ⊥ reflects multiple-scattering interactions entering deep into the mica structure, beyond the tetrahedral sheet and well into the octahedral sheet. Such contributions reflect both changes in the anions coordinating the octahedral cations and increasing total amount of heavy atoms (essentially Fe), and differ based on electronic properties such as oxidation states (e.g., Fe2+ and Fe3+). Therefore, angle-dependent XANES spectroscopy is one of the rare spectroscopic techniques able not only to detect, but also to quantify structural effects in the atoms at the medium- to long-range order.

Near-edge features of Al x-ray absorption near-edge structure (XANES) spectra in aluminosilicate compounds with mixed coordination number are usually assigned to a fourfold coordinated site contribution followed by a sixfold coordinated site contribution that is displaced towards higher energy because of the increasing ligand nucleus potentials, neglecting possible contributions due to bond distance variations and local geometrical distortion. Here we present and discuss the Al K-edge XANES spectra of synthetic micas with either fourfold coordinated Al (phlogopite), or with sixfold coordinated Al (polylithionite), as well as with mixed coordination (preiswerkite). Multiple scattering simulations of XANES spectra demonstrate that octahedral contributions may overlap the tetrahedral ones so that the lower energy structures in mixed coordination compounds may be associated with the octahedral sites. This unexpected behaviour can be described as due to the effect of a significant reduction of the ligand field strength (i.e. large local distortion and Al-O bond distances).

The structure of aluminosilicate melts and/or glasses plays a key role in the earth sciences for the understanding of rock-forming igneous processes, as well as in the materials sciences for their technical applications. In particular, the alkaline-earth aluminosilicate glasses are an extremely important group of materials, with a wide range of commercial application, as well as serving as an analog for natural basaltic melts. However, definition of their structure and properties is still controversial, and in particular the role and effect of Al has long been a subject of debate. Here we report a series of experimental x-ray absorption near-edge structure spectra at the Al K edge on a series of synthetic glasses of peralkaline composition in the $\mathrm{CaO}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}\ensuremath{-}{\mathrm{SiO}}_{2}$ system, together with a general theoretical framework for data analysis based on an ab initio full multiple-scattering theory. We propose an Al/Si tetrahedral network model for aluminosilicate glasses based on distorted polyhedra, with varying both the $T\ensuremath{-}\mathrm{O} (T=\mathrm{Al}$ or Si) bond lengths and the $T\ensuremath{-}\mathrm{O}\ensuremath{-}T$ angles, and with different Al/Si composition. This model achieves a significant agreement between experiments and simulations. In these glasses, experimental data and theoretical results concur to support a model in which Al is network former with a comparatively well ordered local medium-range order (up to 5 \AA{}).