Yasuhiro Inada

In situ time-resolved XAFS analysis of silver particle formation by photoreduction in polymer solutions

Formation mechanisms of silver (Ag) particles in an aqueous ethanol solution of poly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction of AgClO(4) were investigated by using UV-Vis, transmission electron microscopy (TEM), extended X-ray absorption fine structure (XAFS), and in situ energy-dispersive X-ray absorption fine structure (in situ DXAFS) measurements. The average diameter of the Ag particles prepared in the presence and absence of benzoin as a photo-activator was estimated from TEM to be 7.4 and 5.1 nm, respectively, and their particle size distributions ranged from 2 to 15 nm. XAFS analysis indicated that metallic Ag particles were synthesized, and the reduction rate of Ag(+) to Ag(0), the creation of Ag(0)-Ag(0) bonds and their particle growth by the association of Ag(0)-Ag(0) was regulated by the metal concentration and the inclusion of benzoin. In situ DXAFS measurements were performed in real time to investigate the kinetics of Ag(+) reduction and Ag particle formation. During the induction period the reduction of Ag(+) to Ag(0) occurred, and subsequent nucleation and growth process concurrently proceeded after the induction period. The intermediate small Ag particles (C.N. smaller than about 4) were generated in the nucleation process, and grown up to larger particles (C.N.s equal to 4.5+/-1.5) in the longer-duration photoreduction.

In Situ Time-Resolved XAFS Studies of Metal Particle Formation by Photoreduction in Polymer Solutions

Formation mechanisms of metal particles (rhodium (Rh) and palladium (Pd) particles) in an aqueous ethanol solution of poly(N-vinyl-2-pyrrolidone) (PVP) by photoreduction were investigated by UV-vis, transmission electron microscopy (TEM), and in situ X-ray absorption fine structure (in situ XAFS). The average diameter of the Rh and Pd particles prepared by the photoreduction was estimated from TEM to be 2.2 and 2.0 nm, respectively. In situ energy-dispersive XAFS (in situ DXAFS) measurements were performed to investigate the reduction process of Rh(III) and Pd(II) aqua chlorocomplexes as well as their particle formation process. The reduction rate of these aqua chlorocomplexes could be quantitatively evaluated from the change of X-ray absorbance assigned to the contribution of metal-chloride bonds in these complexes. The reduction rate of Rh(III) aqua chlorocomplexes was found to be slower than that of Pd(II). It was also demonstrated that the reduction process of Rh(III) complexes possessed an induction period before the onset of Rh particle formation, although the Pd(II) complexes displayed no induction period, since the reduction of Pd(II) occurred immediately after mixing of an ethanol solution of Pd(II) complexes with aqueous PVP solutions.

Librational, vibrational, and exchange motions of water molecules in aqueous Ni(II) solution: classical and QM/MM molecular dynamics simulations

Abstract The librational and vibrational motions of water molecules in the first and second hydration spheres of the Ni 2+ ion were evaluated by means of velocity autocorrelation functions obtained by classical and combined quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations. The rotational frequencies around three principal axes and the intramolecular vibrational frequencies of the water molecule were calculated using normal-coordinate analyses. The rate constant of the water exchange in the second hydration sphere of the Ni 2+ ion was estimated to be ca. 5×10 10 s −1 . A water-exchange mechanism with an associative character appears to be predominant, but less associative exchanges are also observed.

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

The dynamic behavior and kinetics of the structural transformation of supported bimetallic nanoparticle catalysts with synergistic functions in the oxidation process are fundamental issues to understand their unique catalytic properties as well as to regulate the catalytic capability of alloy nanoparticles. The phase separation and structural transformation of Pt(3)Sn/C and PtSn/C catalysts during the oxidation process were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques, which are element-selective spectroscopies, at the Pt L(III)-edge and the Sn K-edge. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticles on carbon surfaces. The kinetic parameters and mechanisms for the oxidation of the Pt(3)Sn/C and PtSn/C catalysts were determined by time-resolved XAFS techniques. The oxidation of Pt to PtO in Pt(3)Sn/C proceeded via two successive processes, while the oxidation of Sn to SnO(2) in Pt(3)Sn/C proceeded as a one step process. The rate constant for the fast Pt oxidation, which was completed in 3 s at 573 K, was the same as that for the Sn oxidation, and the following slow Pt oxidation rate was one fifth of that for the first Pt oxidation process. The rate constant and activation energy for the Sn oxidation in PtSn/C were similar to those for the Sn oxidation in Pt(3)Sn/C. In the PtSn/C, however, it was hard for Pt oxidation to PtO to proceed at 573 K, where Pt oxidation was strongly affected by the quantity of Sn in the alloy nanoparticles due to swift segregation of SnO(2) nanoparticles/layers on the Pt nanoparticles. The mechanisms for the phase separation and structure transformation in the Pt(3)Sn/C and PtSn/C catalysts are also discussed on the basis of the structural kinetics of the catalysts themselves determined by the in situ time-resolved DXAFS and QXAFS.

Time-resolved DXAFS study on the reduction processes of Cu cations in ZSM-5

The time-resolved reduction process of copper cations in/on ZSM-5 during temperature-programmed reduction (300–700 K) was studied by energy-dispersive X-ray absorption fine structure (DXAFS) as well as transmission electron microscopy (TEM). Two Cu-ZSM-5 samples with different Cu loadings were prepared by an ion-exchange method. The Cu K-edge DXAFS spectra for isolated Cu2+ species in the channels of ZSM-5 and CuO particles on the outer surfaces of ZSM-5 were recorded at an interval of 1 s during the reduction. The curve fitting analysis of the EXAFS data and the XANES analysis revealed that the isolated Cu2+ species in the channels were reduced stepwise. They were reduced to isolated Cu+ species at 400–450 K and the Cu+ species to Cu0 metallic clusters at 550–650 K. Small clusters like Cu4 were initially formed, followed by particle growth. A small part of them went out to the outer surfaces of ZSM-5 during the reduction. In contrast, CuO particles on the outer surfaces were reduced directly to Cu0 metallic particles around 450 K.

In situ time-resolved DXAFS for the determination of kinetics of structural changes of H-ZSM-5-supported active Re-cluster catalyst in the direct phenol synthesis from benzene and O2

Dynamic structural changes and their kinetics of a Re(10)-cluster catalyst in the direct phenol synthesis from benzene and O(2) were investigated by in situ time-resolved Re L(III)-edge energy-dispersive XAFS (DXAFS). We have successfully monitored the structural transformation of active Re(10) clusters to inactive Re monomers in the course of the selective oxidation of benzene with O(2) on the catalyst by the DXAFS technique in a real time. The results obtained suggested that the Re(10) cluster transformed directly to the Re monomers, which showed first order kinetics with respect to the quantity of Re(10) clusters. The absence of undesirable intermediate structures with low phenol selectivity during the structural transformation may be an advantageous issue for the high phenol selectivity of 93.9% at 9.9% conversion in a pulse reaction and 87.7% at 5.8% conversion in a steady-state reaction on the Re(10)-cluster catalyst. The reactant benzene inhibited the unfavorable structural transformation of the Re(10) cluster to the Re monomers during the selective benzene oxidation to phenol.

Ionic Conduction in Lithium Ion Battery Composite Electrode Governs Cross-sectional Reaction Distribution

Composite electrodes containing active materials, carbon and binder are widely used in lithium-ion batteries. Since the electrode reaction occurs preferentially in regions with lower resistance, reaction distribution can be happened within composite electrodes. We investigate the relationship between the reaction distribution with depth direction and electronic/ionic conductivity in composite electrodes with changing electrode porosities. Two dimensional X-ray absorption spectroscopy shows that the reaction distribution is happened in lower porosity electrodes. Our developed 6-probe method can measure electronic/ionic conductivity in composite electrodes. The ionic conductivity is decreased for lower porosity electrodes, which governs the reaction distribution of composite electrodes and their performances.

Chlorides behavior in raw fly ash washing experiments

Chloride in fly ash from municipal solid waste incinerators (MSWIs) is one of the obstructive substances in recycling fly ash as building materials. As a result, we have to understand the behavior of chlorides in recycling process, such as washing. In this study, we used X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) to study the chloride behavior in washed residue of raw fly ash (RFA). We found that a combination of XRD and XANES, which is to use XRD to identify the situation of some compounds first and then process XANES data, was an effective way to explain the chlorides behavior in washing process. Approximately 15% of the chlorine in RFA was in the form of NaCl, 10% was in the form of KCl, 51% was CaCl(2), and the remainder was in the form of Friedels salt. In washing experiments not only the mole percentage but also the amount of soluble chlorides including NaCl, KCl and CaCl(2) decreases quickly with the increase of liquid to solid (L/S) ratio or washing frequency. However, those of insoluble chlorides decrease slower. Moreover, Friedels salt and its related compound (11CaO.7Al(2)O(3).CaCl(2)) were reliable standards for the insoluble chlorides in RFA, which are strongly related to CaCl(2). Washing of RFA promoted the release of insoluble chlorides, most of which were in the form of CaCl(2).

A New XAFS Beamline NW10A at the Photon Factory

A new XAFS beamline NW10A using bending magnet radiation from 6.5 GeV PF‐AR has been constructed. NW10A consists of a Si(311) double crystal monochromator and a Pt‐coated bent cylindrical focusing mirror and provides focused X‐ray beam between 8 and 42 keV. The obtained flux through a 1mm square slit is 1×1010 ph/s at 20 keV and 7×109 ph/s at 30keV, which are 20 and 200 times more intense than obtained at BL‐10B. Platinum K‐edges do not degrade the quality of XAFS spectra when higher orders are properly reduced. High quality Ce K‐edge XAFS spectra are easily obtained.

High‐pressure stopped‐flow nuclear magnetic resonance apparatus for the study of fast reactions in solution

A high‐pressure proton nuclear magnetic resonance (NMR) probe for a stopped‐flow method has been developed, which enables us to follow fast reactions at various pressures up to 200 MPa. The high‐pressure stopped‐flow NMR (HP‐SF‐NMR) method has been applied to the study of several reactions at high pressures: the reaction of tetramethyltin with iodine in chloroform and the solvent exchange reaction on aluminum(III) ion in N, N‐dimethylformamide. The volumes of activation for the iodomerization of tin and the solvent exchange reaction on aluminum(III) were determined to be −24.9±3.8 cm3 mol−1 and −2.2±0.8 cm3 mol−1, respectively. The apparatus permits measurement of activation volumes for reactions with half lives longer than a few seconds if the nuclear relaxation time of the measured proton is short enough. Several requirements for the applicability of HP‐SF‐NMR are discussed.