Development of a new in-laboratory XAFS apparatus based on new concept

Hydrothermally synthesized poorly-crystalline binary oxides with ZrW2O8 composition: preparation, structural analysis, and catalytic activity for the alkylation of anisole with benzyl alcohol

Hydrothermally synthesized poorly-crystalline metastable Zr–W binary hydroxide (W/Zr = 2), after calcination, was confirmed to be a strong solid acid catalyst to promote the alkylation of anisole with benzyl alcohol. The preparation conditions, structure of the as-prepared catalysts and the calcined hydroxides were investigated using XRD, nitrogen adsorption isotherms, TG-DTA, and XANES/EXAFS techniques. The crystalline phase was controlled by the hydrochloric acid concentration used for preparing a mother gel, and 5–9 M HCl was suitable for preparing the active phase. The tungsten species exists as a six-valent WO₆ distorted octahedron connected with the ZrO₇ unit via corner-sharing linkages. The incompleteness of the network structure is suggested to be responsible for the solid acidity.

Hydrothermally synthesized poorly-crystalline metastable Zr–W binary hydroxide (W/Zr = 2), after calcination, was confirmed to be a strong solid acid catalyst to promote the alkylation of anisole with benzyl alcohol.

Characterization of Li-S Batteries Using Laboratory Sulfur X-ray Emission Spectroscopy

Application of laboratory-based X-ray analytical techniques that are capable of a reliable characterization of the chemical state of sulfur within bulk battery cathode in parallel with electrochemical characterization is essential for further development of lithium-sulfur batteries. In this work, MeV proton-induced X-ray emission (XES) sulfur measurements were performed in ex situ mode on laboratory-synthesized sulfur standards and precycled battery cathodes. The average sulfur charge was determined from the energy shift of the Kα emission line and from the spectral shape of the Kβ emission spectrum. Finally, operando Kα XES measurements were performed to monitor reduction of sulfur within battery cathode during discharge. The experimental approach presented here provides an important step toward more routine laboratory analysis of sulfur-based battery systems and also other sulfur-neighboring low-Z bulk materials with emission energies in the tender X-ray range.

Detailed Molecular and Structural Analysis of Dual Emitter IrQ(ppy)2 Complex

The molecular structure of the 8-hydroxyquinoline–bis (2-phenylpyridyl) iridium (IrQ(ppy)₂) dual emitter organometallic compound is determined based on detailed 1D and 2D nuclear magnetic resonance (NMR), to identify metal-ligands coordination, isomerization and chemical yield of the desired compound. Meanwhile, the extended X-ray absorption fine structure (EXAFS) was used to determine the interatomic distances around the iridium ion. From the NMR results, this compound IrQ(ppy)₂ exhibits a trans isomerization with a distribution of coordinated N-atoms in a similar way to facial Ir(ppy)₃. The EXAFS measurements confirm the structural model of the IrQ(ppy)₂ compound where the oxygen atoms from the quinoline ligands induce the splitting of the next-nearest neighboring C in the second shell of the Ir³⁺ ions. The high-performance liquid chromatography (HPLC), as a part of the detailed molecular analysis, confirms the purity of the desired IrQ(ppy)₂ organometallic compound as being more than 95%, together with the progress of the chemical reactions towards the final compound. The theoretical model of the IrQ(ppy)₂, concerning the expected bond lengths, is compared with the structural model from the EXAFS and XRD measurements.

Ga Ion-doped ZrO2 Catalyst Characterized by XRD, XAFS, and 2-Butanol Decomposition

Group 2, 3, and 13 element-doped zirconium oxide catalysts M-ZrO₂ (M = Mg, Sr, Y, La, Ce, Sm, Er, Yb, B, Al, Ga, In, and Tl; 5 mol%) were prepared by impregnation of each metal salt aqueous solution on amorphous zirconium hydroxide, followed by calcination at 773 K. The M-ZrO₂ samples were characterized by the catalytic performance of 2-butanol decomposition at 573 K, XRD, XANES and EXAFS spectroscopic techniques. Detailed analyses were performed herein for a series of Ga-ZrO₂ with various doping amounts in the range of 1 - 60 mol%. The addition of Group 2 and 3 elements little influenced the catalytic performance of ZrO₂ itself to promote dehydration to produce 1-butene with 90% selectivity. Ga-ZrO₂ and In-ZrO₂ gave methyl ethyl ketone as the main product via dehydrogenation. The doped Ga ion mainly existed inside the bulk of zirconia by forming the Ga_xZr_1-xO₂ solid solution up to 5 mol%. Highly doped species more than 10 mol% aggregated to form ε-Ga₂O₃. Each fraction forming the solid solution and Ga₂O₃-like species was evaluated by XANES analysis.

In-house setup for laboratory-based x-ray absorption fine structure spectroscopy measurements

We report on a laboratory-based facility for in-house x-ray absorption fine structure (XAFS) measurements. The device consists of a conventional x-ray source for the production of the incident polychromatic radiation and a von Hamos bent crystal spectrometer for the analysis of the incoming and transmitted radiation. The reliability of the laboratory-based setup was evaluated by comparing the Cu K-edge and Ta L₃-edge XAFS spectra obtained in-house with the corresponding spectra measured at a synchrotron radiation facility. To check the accuracy of the device, the K- and L-edge energies and the attenuation coefficients below and above the edges of several 3d, 4d, and 5d elements were determined and compared with the existing experimental and theoretical data. The dependence of the XAFS spectrum shape on the oxidation state of the sample was also probed by measuring inhouse the absorption spectra of metallic Fe and two Fe oxides (Fe₂O₃ and Fe₃O₄).

A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements

We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10(6)-10(7) photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.

pH-dependence of selenate removal from liquid phase by reductive Fe(II)-Fe(III) hydroxysulfate compound, green rust

Removal of selenate ion from the liquid phase by hydroxysulfate green rust (GR(SO4)) was investigated in the pH range from 7.5 to 10.0. Batch tests showed that the total selenium concentration decreased more rapidly with increasing pH. However, the amount of selenium removed from the liquid phase increased as the pH decreased. X-ray absorption spectrometric analysis demonstrated that the Se(VI) in the selenate ion was reduced to elemental selenium Se(0) at pH 9.0, whereas the existence of small amount of intermediate Se(IV) was detected at pH 7.5. Comparing the mass balance of the amount of consumed ferrous iron in GR(SO4), [DeltaFe(II)], and the amount of Se(VI) removed from the liquid phase, [DeltaSe(VI)], [DeltaFe(II)] is approximately six times larger than [DeltaSe(VI)] in mol units. This is also indirect but convincing evidence that the oxidation of Fe(II) in GR(SO4) leads to the simultaneous reduction of Se(VI) to Se(0). Powder X-ray diffraction analysis showed that the end product of GR(SO4) depends on the pH: magnetite for pH>9.0, goethite for pH<8.0, and their mixture at pH 8.5. These results indicate that the solution pH has a significant effect on the reaction path of selenate removal by GR(SO4).