Automatic XAFS measurement system developed at BL14B2 in SPring-8

The Inner Shell Spectroscopy beamline at NSLS-II: a facility for in situ and operando X-ray absorption spectroscopy for materials research

The Inner Shell Spectroscopy (ISS) beamline on the 8-ID station at the National Synchrotron Light Source II (NSLS-II), Upton, NY, USA, is a high-throughput X-ray absorption spectroscopy beamline designed for in situ, operando, and time-resolved material characterization using high monochromatic flux and scanning speed. This contribution discusses the technical specifications of the beamline in terms of optics, heat load management, monochromator motion control, and data acquisition and processing. Results of the beamline tests demonstrating the quality of the data obtainable on the instrument, possible energy scanning speeds, as well as long-term beamline stability are shown. The ability to directly control the monochromator trajectory to define the acquisition time for each spectral region is highlighted. Examples of studies performed on the beamline are presented. The paper is concluded with a brief outlook for future developments.

Fully automated measurement system for temperature-dependent X-ray total scattering at beamline BL04B2 at SPring-8

Data-driven approaches in materials science demand the collection of large amounts of data on the target materials at synchrotron beamlines. To accurately gather suitable experimental data, it is essential to establish fully automated measurement systems to reduce the workload of the beamline staff. Moreover, the recent COVID-19 pandemic has further emphasized the necessity of automated and/or remote measurements at synchrotron beamlines. Here, the installation of a new sample changer combined with a high-temperature furnace and a fully automated alignment system on beamline BL04B2 at SPring-8 is reported. The system allows X-ray total scattering measurements of up to 21 samples at different temperatures (from room temperature to 1200°C) to be conducted without any human assistance.

Optically Transparent Colloidal Dispersion of Titania Nanoparticles Storable for Longer than One Year Prepared by Sol/Gel Progressive Hydrolysis/Condensation

The molecular catalyst sensitized system (MCSS), where an excited molecular catalyst adsorbed on a semiconductor such as TiO₂ injects electrons to the conduction band of the semiconductor leading to hydrogen evolution/CO₂ reduction coupled with an oxidation of water on the molecular catalyst, has been one of the most probable candidates in the approach to artificial photosynthesis. For a full utilization of visible light, however, a serious light scattering of the aqueous suspension of TiO₂ in the visible region, which is generally experienced, should be avoided. Here, we report a preparation of optically transparent colloidal dispersion of TiO₂ by the sol/gel reaction of TiCl₄ through progressive hydrolysis/condensation under the basic condition without any calcination processes. The TiO₂ nanoparticles (TiO₂(NPs)) obtained were characterized as an amorphous particle (∼10-15 nm) having a microcrystal domain of anatase within several nm by XRD, Raman spectroscopies, XRF, XAFS, TG/DTA, and HRTEM, respectively. The energy-resolved distribution of carrier electron traps in TiO₂(NPs) as a fingerprint of TiO₂ was characterized through reversed double-beam photo-acoustic spectroscopy to have a close similarity to that of TiO₂(ST-01) as well as the observation of carrier traps by transient absorption spectroscopy. Though the powder TiO₂(NP) itself was not dispersed well in aqueous solution, the wet TiO₂(NPs) as prepared before being dried up provided a completely transparent aqueous dispersion under the acidic condition (1 M HCl). Addition of methanol enabled the colloidal dispersion (TiO₂(NPs, MeOH/H₂O, 0.1 M HCl)) to keep the optical transparency for longer than 1 year (550 days), which is the first example of TiO₂ dispersion storable for such a long period. TiO₂(NPs, MeOH/H₂O) exhibited a moderate photocatalytic reactivity of H₂ evolution with a quantum yield of ∼2.6% upon 365 nm light irradiation. An optically transparent thin film of TiO₂(NPs, MeOH/H₂O) was also successfully prepared on a glass plate to exhibit an enhanced hydrophilicity upon UV light irradiation.

Steps towards XAFS beamline automation and remote access

Although remote access to beamline synchrotron facilities is now a common operation mode at macromolecular crystallography beamlines thanks to substantial efforts in automated processes for sample preparation and handling, experiment planning and analysis, this is still not the case for XAFS beamlines. Here the experience and developments undertaken at LNLS and Diamond in automation are described, in an attempt to tackle the specific challenges posed by the high variability in experimental conditions and configurations that XAFS measurements require.

Wacker Oxidation of Terminal Alkenes Over ZrO2 -Supported Pd Nanoparticles Under Acid- and Cocatalyst-Free Conditions

Highly efficient Wacker oxidation of aromatic or aliphatic terminal alkenes into methyl ketones and benzofurans is developed by using reusable Pd⁰ nanoparticles (NPs) supported on ZrO₂ under acid- and cocatalyst-free conditions. Molecular oxygen or air can be utilized as the terminal oxidant, which results in the formation of H₂ O as the only theoretical byproduct. The activation of the Pd NPs by O₂ plays an important role in promoting this reaction. Interestingly, PdO supported on ZrO₂ showed no activity. Additionally, the Pd particle size significantly affects the catalytic activity, with an apparent optimal diameter of 4-12 nm. In addition to the heterogeneous catalyst forms, the Pd NPs can be generated from a Pd⁰ complex during the reaction, and these particles are even recyclable.

A hyperspectral X-ray computed tomography system for enhanced material identification

X-ray computed tomography (CT) can distinguish different materials according to their absorption characteristics. The hyperspectral X-ray CT (HXCT) system proposed in the present work reconstructs each voxel according to its X-ray absorption spectral characteristics. In contrast to a dual-energy or multi-energy CT system, HXCT employs cadmium telluride (CdTe) as the x-ray detector, which provides higher spectral resolution and separate spectral lines according to the material's photon-counter working principle. In this paper, a specimen containing ten different polymer materials randomly arranged was adopted for material identification by HXCT. The filtered back-projection algorithm was applied for image and spectral reconstruction. The first step was to sort the individual material components of the specimen according to their cross-sectional image intensity. The second step was to classify materials with similar intensities according to their reconstructed spectral characteristics. The results demonstrated the feasibility of the proposed material identification process and indicated that the proposed HXCT system has good prospects for a wide range of biomedical and industrial nondestructive testing applications.

Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity

Decarbonylation of furfural to furan was efficiently catalyzed by ZrO₂ -supported Pd clusters in the liquid phase under a N₂ atmosphere without additives. Although Pd/C and Pd/Al₂ O₃ have frequently been used for decarbonylation, Pd/ZrO₂ exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO₂ . ZrO₂ with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al₂ O₃ despite their high surface areas. The catalytic activity of Pd/ZrO₂ was enhanced with a decrease in particle size, and the smallest Pd/ZrO₂ was the most active catalyst for decarbonylation. When CeO₂ was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO₂ with a high surface area, with a strong interaction through the formation of a Pd-O-Ce bond, which led to a lower catalytic activity than that of Pd/ZrO₂ . This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO₂ maintained its catalytic activity until its sixth use.

Direct C-H arene homocoupling over gold nanoparticles supported on metal oxides

The direct CH/CH bond coupling of dimethyl phthalate was performed successfully over supported gold nanoparticle catalysts. Gold on reducible metal oxides, such as Co3 O4 , and on inert oxides that have an oxygen-releasing capacity, such as ZrO2 , showed the highest catalytic activity for the production of biphenyl tetracarboxylate using O2 as the sole oxidant. Supported Pd(OH)2 also catalyzed the reaction, but the catalytic activity was inferior to that of gold. Moreover, the gold catalysts exhibited excellent regioselectivity for the synthesis of valuable 3,3',4,4'-tetrasubstituted biphenyls by coupling with each other at the 4-position without the need for additional ligands. Gold catalysts also promoted the oxidative homocoupling of arenes including o-xylene to give symmetrical biaryls with high regioselectivity. X-ray absorption fine structure measurements revealed that the catalytically active species was Au(0) and that the lattice oxygen of Co3 O4 played an important role in the gold-catalyzed oxidative coupling. The results of the kinetic studies were consistent with an electrophilic aromatic substitution pathway. Regioselectivity is not controlled by directing groups or the electronic character of the substituents but by steric hindrance, which suggests that gold nanoparticles not only catalyze the oxidative coupling but also act as bulky ligands to control the regioselectivity.

Aerobic oxidation of cyclohexanones to phenols and aryl ethers over supported Pd catalysts

ZrO₂ supported palladium catalysts promoted the aerobic oxidation of cyclohexanones to give phenols and aryl ethers.

Base-free direct oxidation of 1-octanol to octanoic acid and its octyl ester over supported gold catalysts

The choice of a suitable support for gold nanoparticles (Au NPs) enabled the direct oxidation of unreactive aliphatic alcohol, 1-octanol, to octanoic acid and octyl octanoate in the absence of a base. Under optimized conditions, Au NPs supported on NiO (Au/NiO) exhibited remarkably high catalytic activities and excellent selectivities to octanoic acid (e.g., 97 %) at full conversion. In contrast to Au/NiO, Au/CeO₂ selectively produced octyl octanoate as a major product in a base-free aqueous solution with a maximum selectivity of 82 % under optimized conditions.