Kiyotaka Asakura

XAFS Techniques for Catalysts, Nanomaterials, and Surfaces

Introduction to XAFS.- History of XAFS for catalysts and surfaces.- Present status of XAFS .- Theory and analysis of XAFS.- Theory of EXAFS.- Theory of XANES.- Analysis of EXAFS and XANES.- Sources and measurement methods for XAFS.- SR sources.- Bending magnets and Wigglers.- Undulator.- XFEL.- Measurements and detectors.- Cell designs.- Advanced XAFS techniques.- In-situ XAFS under catalytic and extreme conditions.- Time-resolved XAFS.- Quick.- Dispersive.- Pump-Probe.- Spatially resolved XAFS.- Micro-XAFS and Nano-XAFS.- XAFS imaging.- In-operando XAFS.- XAFS for ultra dilute systems.- Total reflection XAFS and related XAFS.- High energy resolution XAFS.- XAFS Raman.- Oak Ridge and European Synchrotron Facilities.- XANES applications.- XAFS Applications.- Catalytic nanoclusters and nanoparticles.- Nano oxides and zeolites.- Chemically designed surfaces for catalysts.- Fuel cells.- Batteries.- Surfaces.- Sensors.- Bimetallic materials.- homogeneous catalysts.- Enzymes and models.- Green Catalysts.- Environmental catalysts.- Solid/liquid interfaces.- choice from Oak Ridge.- choice from European Synchrotron Facilities.

Structural analysis of strontium in human teeth treated with surface pre-reacted glass-ionomer filler eluate by using extended X-ray absorption fine structure analysis

The bioactive effects of strontium released from surface pre-reacted glass-ionomer (S-PRG) fillers may aid in caries prevention. In this study, the local structure of strontium taken up by teeth was estimated by extended X-ray absorption fine structure analysis. Immersing teeth into S-PRG filler eluate increased the strontium content in enamel and dentin by more than 100 times. The local structure of strontium in enamel and dentin stored in distilled water was the same as that in synthetic strontium-containing hydroxyapatite (SrHAP). Moreover, the local structure of strontium in enamel and dentin after immersion in the S-PRG filler eluate was also similar to that of SrHAP. After immersion in the S-PRG filler eluate, strontium was suggested to be incorporated into the hydroxyapatite (HAP) of enamel and dentin at the calcium site in HAP.

Portable ultrahigh-vacuum sample storage system for polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy

A portable ultrahigh-vacuum sample storage system was designed and built to investigate the detailed geometric structures of mass-selected metal clusters on oxide substrates by polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy (PTRF-XAFS). This ultrahigh-vacuum (UHV) sample storage system provides the handover of samples between two different sample manipulating systems. The sample storage system is adaptable for public transportation, facilitating experiments using air-sensitive samples in synchrotron radiation or other quantum beam facilities. The samples were transferred by the developed portable UHV transfer system via a public transportation at a distance over 400u2009km. The performance of the transfer system was demonstrated by a successful PTRF-XAFS study of Pt4 clusters deposited on a TiO2(110) surface.

X-Ray-Aided Noncontact Atomic Force Microscopy

X-ray-aided noncontact atomic force microscopy (XANAM) is a spectroscopic and imaging technique in the combination of noncontact atomic force microscopy (NC-AFM) and synchrotron radiation (SR) X-ray, providing chemical imaging of sample surface beneath the AFM tip (Suzuki in J Phys: Conf Ser 61:1117–1121, 2007; Suzuki in Bull. Chem Soc Jpn 88:240–250, 2015[1]).

The challenge of constructing an international XAFS database

The present situation of the XAFS database in Japan and a proposal for the construction of an international collaboration XAFS database are presented.

Trace mono-atomically dispersed rhodium on zeolite-supported cobalt catalyst for the efficient methane oxidation

The partial oxidation of methane is a promising method for the efficient production of syngas. To implement this process using common stainless steel reactors, an inexpensive catalyst that functions at 650u2009°C or below is necessary. However, base metal catalysts typically require much higher temperatures, and they are deactivated by re-oxidation and coke formation. Here we report that modification of a zeolite-supported 3 wt% cobalt catalyst with a trace amount of mono-atomically dispersed rhodium (0.005 wt%) dramatically improves catalytic performance and durability. Cobalt/mordenite is nearly inactive due to the oxidation of cobalt, but the catalyst modified with rhodium continuously gives 85–86% methane conversion and 90–91% CO selectivity with an H2/CO ratio of 2.0 without serious coking at 650u2009°C. During the reaction, mono-atomically dispersed rhodium converts cobalt oxide to Co0 active species via hydrogen spillover. Use of the zeolite support is key to the high catalytic performance.Partial oxidation of methane is an efficient route to syngas, and would benefit from base metal catalysts which operate below 650u2009°C. Here, the authors demonstrate that modification of a zeolite-supported cobalt catalyst with trace rhodium improves both catalyst activity and durability under such conditions.

Development of Surface Fluorescence X-ray Absorption Fine Structure Spectroscopy using a Laue-Type Monochromator

Surface fluorescence X-ray absorption fine structure (XAFS) spectroscopy using a Laue-type monochromator has been developed to acquire structural information about metals with a very low concentrate on a flat highly oriented pyrolytic graphite (HOPG) surface in the presence of electrolytes. Generally, surface fluorescence XAFS spectroscopy is hindered by strong scattering from the bulk, which often chokes the pulse counting detector. In this work, we show that a bent crystal Laue analyzer (BCLA) can efficiently remove the scattered X-rays from the bulk even in the presence of solution. We applied the technique to submonolayer (∼1014 u2005atoms cm-2 ) Pt on HOPG and successfully obtained high signal/noise inu2005situ XAFS data in combination with back-illuminated fluorescence XAFS (BI-FXAFS) spectroscopy. This technique allows inu2005situ XAFS measurements of flat electrode surfaces to be performed in the presence of electrolytes.

EXAFS study of Ti0.98Pd0.02O2-δ catalyst

To understand the higher catalytic properties, the structure of 2 at. % palladium supported on TiO2 has been investigated by Extended X-ray absorption fine structure (EXAFS) spectroscopy. This nanocatalytic material of composition Ti0.98Pd0.02O2-δ has been synthesized by solution combustion method The analysis of EXAFS shows the oxide ion sublattice aroundPd ions is destabilized in the solid solution. Instead of ideal six coordination, Pd ion has 4+2, coordinations creating long and short bonds. The long Pd–O bonds are at 2.52 A which are much higher than average Ti–O bonds of 1.947 A.

A Spring-8 new beam line for the fuel cell analysis

BL36XU is a new beam line in SPring-8 dedicated to the fuel cell analysis using cutting-edge XAFS techniques[1,2]. A tapered undulator emits a highly brilliant X ray with the energy range of 4.5 keV -35 keV which enables us to carry out high timeresolution Quick XAFS (10 ms) , 2 D and 3D microXAFS. For the higher time-resolution XAFS measurement, Dispersive XAFS with 100 micro s time resolution is available. In addition the near ambient pressure (NAP)-XPS is installed in the same beam line and the electronic state of fuel cell catalysts is analyzed under the working conditions. The beam line has a high energy resolution monochromator for X-ray emission spectroscopy as well as bent crystal Laue analyser for highly sensitive fluorescence XAFS less than 1 ML. We discuss the possibility of the future XAFS spectroscopies.