泉 康雄

The UV-induced self-assembly of [Mo7O24](6-) to 28-etectron-reduced {Mo-142} at pH 3.4 was monitored by Mo Kedge XAFS spectra of photolytes. The EXAFS curve fit analysis indicates that the accumulation of [MoO4](2-) in an equilibrium with {Mo-8} was accompanied by the formation of two-electron-reduced {Mo-14}, and the subsequent construction of the {Mo-20} and {Mo-21} building blocks provided {Mo-142} through their reductive condensation.

Platinum nanoparticles have been reported with mean sizes between 1.5 and 7 nm supported on carbon, The contact between Pt nanoparticles and C has never been controlled and monitored nanoscopically. In this paper, stable Pt nanoparticles with a mean size of 1.2 nm were synthesized embedded on/in a C matrix catalytically produced from acetylene over the Pt nanoparticles. The replica Pt-C composite was synthesized inside of the ordered mesopores (2.7 nm) of Al-MCM-41 followed by removal of the template. The contact between the Pt nanoparticle and C was experimentally observed by high-energy resolution Pt L(2)-edge XANES spectra tuned to 11065.7 eV, at a lower energy by 5 eV than the Pt L beta(1) peak top for the replica Pt-C pressed to electrolyte polymer (Nafion). The spectra were nicely reproduced in a theoretical spectrum using ab initio multiple scattering calculations for the interface Pt site between cuboctahedral Pt(38) and graphite layers. Other Pt sites detected in state-selective Pt L(2)-edge XANES were exclusively metallic for replica Pt-C/Nafion either in air or in H, The thus-characterized replica Pt-C composite was tentatively tested as a cathode of H(2)-air polymer electrolyte fuel cell in comparison to commercial 20 wt % Pt/Vulcan XC-72 as the cathode. The improvement of Pt dispersion stabilized on/in a C matrix, effective contact of Pt with C, and diffusion of O(2) in a few nanometers of replica Pt-C powder was suggested,

Mesostructured iron oxyhydroxide (FeOx) and iron oxyhydroxide-phosphate (FeOxP) composites were organized using dodecylsulfate surfactant as a template. X-ray diffraction studies depicted a lamellar structure of the product. Ion exchange and solvent extraction methods were employed for the removal of the surfactant. Carboxylate ions exchanged lamellar type mesostructured material reorganized to a wormhole-like mesoporous material when heated under N2 atmosphere. Surfactant was completely removed by carboxylate ions as observed by the Fourier transform infrared spectra. High surface area acetate-exchanged FeOx (230 m2 g-1) was obtained after the surfactant removal from the composite (2.8 m2 g-1). Surface area of acetate-exchanged FeOxP was the highest (240 m2g-1) after the removal of the surfactant. Local structure of iron species of FeOx was investigated by X-ray absorption fine structure spectroscopy. Further, Fe···Fe bond appeared at 3.21-3.25 Å with coordination number 2-3, showing a high degree of un-saturation of Fe···Fe bonds. As compared with bulk iron oxyhydroxide and iron-intercalated montmorillonite, the mesoporous iron materials were highly effective for arsenic removal from low concentrations of aqueous solutions. Furthermore, mesoporous iron materials were stable in aqueous phase. © Springer Science + Business Media B.V. 2009.

The electronic state and site structure of doped S to enable photocatalysis of TiO2 under visible light were investigated using S K-edge XANES compared to theoretically generated spectra. S sites substituting on the O atoms of TiO2 were predominant and essential in photocatalysis based on S K absorption edge peak energy and post-edge pattern. Minor cationic/elemental S sites were detected as peaks clue to the transition to vacant level of S3p, but most were lost during photocatalysis.

The sulfur K-edge peak energy values in our paper, Journal of Physical Chemistry C 113(16) 6706-6718, were not calibrated. The values were by 0.81 eV greater than the ones given.

Anion doping to titanium oxide (TiO(2)) has been extensively studied to explore visible light-responsive photocatalysts. Among them, sulfur doping was most effective; however, the site structure and the implication to promoted photocatalysis have not been reported yet, except for valence state information based on X-ray photoelectron spectroscopy. Sulfur and/or nitrogen was doped to TiO(2) with a narrow pore size distribution, at 3 nm, using thiourea or urea. They were compared to the uniform mesoporous TiO(2) modified via the chemical vapor deposition (CVD) of hydrogen sulfide and the titanate/TiO(2) nanotube synthesized hydrothermally using TiS(2). In ethanol and O(2) under visible light (wavelengths of >370, >420, >480, >520, or >580 nm), water formation was promoted by a factor of 12, in clear contrast to the only 2.3x enhancement for acetaldehyde formation by doping sulfur. These anion-doped mesoporous TiO(2) catalysts were characterized using Ti and S K-edge extended X-ray absorption fine structure for the first time. The Ti-S bonds were detected at 2.283-2.44 angstrom for sulfur-doped mesoporous TiO(2) using thiourea and sulfur-doped mesoporous TiO(2) via CVD, demonstrating the presence of substitutional anionic S on the O sites. The doped anionic sulfur created impurity level(s) at 0.8-2.2 eV below the conduction band (CB) minimum of mesoporous TiO(2). It enabled the electron excitation to the CB and then to O(2) to convert to water under visible light. In contrast, the impurity level(s) at 0.8-2.2 eV below the CB minimum was/were not effective to (directly or indirectly) receive electrons from the substrate (ethanol/ethoxyl). Preferential water formation under visible light was also observed for TiO(2) nanotubes that were synthesized hydrothermally from TiS(2).

New sorbents were investigated for the effective removal of low concentrations of arsenic and lead to adjust to modern worldwide environmental regulation of drinking water (10 ppb). Mesoporous Fe oxyhydroxide synthesized using dodecylsulfate was most effective for initial 200 ppb of As removal, especially for more hazardous arsenite for human's health. Hydrotalcite-like layered double hydroxide consisted of Fe and Mg was most effective for initial 55 ppb of Pb removal. The molecular removal mechanism is critical for environmental problem and protection because valence state change upon removal of e.g., As on sorbent surface from environmental water may detoxify arsenite to less harmful arsenate. It is also because the evaluation of desorption rates is important to judge the efficiency of reuse of sorbents. To monitor the low concentrations of arsenic and lead on sorbent surface, selective X-ray absorption fine structure (XAFS) spectroscopy was applied for arsenic and lead species adsorbed, free from the interference of high concentrations of Fe sites contained in the sorbents and to selectively detect toxic AsIII among the mixture of AsIII and AsVspecies in sample. Oxidative adsorption mechanism was demonstrated on Fe-montmorillonite and mesoporous Fe oxyhydroxide starting from AsIIIspecies in aqueous solution to AsV by making complex with unsaturated FeOx(OH)y sites at sorbent surface. Coagulation mechanism was demonstrated on double hydroxide consisted of Fe and Mg from the initial 1 ppm of Pb2+aqueous solution whereas the mechanism was simple ion exchange reaction when the initial Pb2+ concentrations were as low as 100 ppb.

Selective oxidation under visible light is attractive for application in environment-benign societies. Oxidative dehydrogenation of ethanol proceeds over mesoporous V-doped TiO2 under visible light in clear contrast to ethanol dehydrogenation over crystalline TiO2 doped or undoped with V and inactive mesoporous TiO2. The red-ox states of V-IV and V-III were detected using X-ray spectroscopies. In this paper, kinetic measurements of each catalytic step and X-ray spectroscopic monitoring under catalytic reaction conditions are correlated. The ethanol conversion to acetaldehyde in the absence of O-2 was monitored under visible light coupled with reduction of V-IV to V-III species based on VK beta(5,2) emission and VK beta(5,2)-selecting X-ray absorption fine structure spectra. The oxidative dehydrogenation of dissociatively adsorbed ethoxyl species proceeded in O-2 Linder visible light with formation rates 38% of steady photo-catalysis in ethanol + O-2. The acetaldehyde desorption step by H Subtraction from ethoxyl species on V-III was found to be rate-limiting. The origin of oxidative dehydrogenation over mesoporous V-TiO2, was suggested to be coordinatively unsaturated V-III species specifically activating O-2 molecules. Further, a poisoning effect of product water was demonstrated to block the active V sites. UV light illumination was found to be effective to re-activate the mesoporous V-TiO2 catalyst.

The heterogeneity of gold sites in various Au/TiO2 catalysts was studied by means of state-sensitive Au L3-edge X-ray absorption fine structure (XAFS) combined with high energy-resolution X-ray fluorescence spectrometry. A series of Au/TiO2 catalysts were prepared via deposition-precipitation method on anatase-type or mesoporous (amorphous) TiO2 added with NaOH (lower Au loading) or urea (higher Au loading). The mean Au particle size ranged between 29 and 87 Å based on high-resolution TEM (transmission electron microscope) measurements. The Au Lα1 emission peak energy for Au/mesoporous-TiO2 in air and Au/anatase-TiO2 in CO (5%) corresponded to Au(0) state. The emission peak energy for Au/anatase-TiO2 in air shifted toward that of Au(I) state. For relatively greater Au particles (average 87 Å) dispersed on mesporous TiO2, the major valence state discriminated by Au Lα1-selecting XANES (X-ray absorption near-edge structure) spectrum tuned to Au Lα1 emission peak top was Au0, but the Auδ- state could be successfully monitored by Au Lα1-selecting XANES tuned to the emission energy at 9707.6 eV, of which population was relatively small compared to the case of smaller Au particles (average 29 Å) on anatase-type TiO2. On the other hand, negative charge transfer from Au 5d to support was demonstrated in Au(δ+)-state sensitive XANES tuned to 9718.3-9718.7 eV. The Au(δ+)-state sensitive XANES spectra resembled theoretically generated XANES for interface Au(δ+) sites model on TiO2 in contact with surface Ti sites. Further charge transfer was demonstrated from Au to adsorbed O2 for Au/anatase-TiO2 catalyst.

Visible light-excited ethanol dehydration reaction steps to adsorb ethanol and then to donate an electron to transform V(IV) to V(III) site exposed on mesoporous V(IV)-TiO2 catalyst were successfully monitored by means of V Kβ5,2-selecting XANES spectroscopy. Spherically-bent Ge(422) crystal was used for the X-ray fluorescence analyses and Xe arc lamp of 500 W was illuminated at 10 mm apart from catalyst samples under on reaction conditions. Specific redox reaction mechanism between V(IV) and V(III) states was proposed for dehydration reaction over the mesoporous V-TiO2 catalyst based on the V Kβ5,2-selecting XANES compared to general vanadium catalysts starting from V(V) state for dehydrogenation reaction.

The photocatalytic role of vanadium doped in mesoporous TiO2 has not been clarified. Valence state-sensitive V Kβ5,2-selecting (5462.9 eV) X-ray absorption fine structure (XAFS) was used to monitor the V sites in mesoporous TiO2 for ethanol dehydration under equilibrium in situ conditions and visible light-illumination. First, the feasibility of discriminating V(IV) sites from a 1:1 physical mixture of standard V(IV) and V(V) inorganic compounds was demonstrated, by tuning the secondary fluorescence spectrometer to 5459.0 eV. The chemical shift of V Kβ5,2 emission between V(IV) and V(V) sites was 1.0 eV. The selection of valence states V(IV) and V(V) was 100% and 80%, respectively. The redox states for ethanol dehydration over mesoporous TiO2 excited in visible light were suggested to be V(III) and V(IV). The chemical shift between valence states V(III) and V(IV) was greater (3.2 eV). On the basis of V Kβ5,2 emission and V Kβ5,2-selecting XAFS spectra tuned to the V Kβ5,2 peak, we determined that the fresh mesoporous V-TiO2 catalyst has a valence state of V(IV). The vanadium sites were partially reduced by the dissociative adsorption of ethanol under visible light, but they still stay within the emission-energy ranges for standard V(IV) compounds. These partially reduced vanadium sites were reoxidized in oxygen under visible light. Finally, direct XAFS observation of photoreduced V(III) sites was attempted by tuning the fluorescence spectrometer to 5456.3 eV for partially reduced mesoporous V-TiO2. Valence state V(III) was selected for 60% of the spectrum in the mixture of V(III)(minor) and V(IV)(dominant) valence states.

Rhodium catalysts were synthesized in ordered mesoporous silica FSM-16 using Rh/Al heteropolyacid anions and/or [Rh(COD)(2)](+) complex. The hydroformylation activity of propene was compared to impregnated Rh/FSM-16 catalysts prepared from rhodium chloride. The catalysts were very selective to produce butanols due to the effect of two-dimensional mesoporous reaction space (effective internal pore diameter 27 A). The selectivity to butanols (n-butanol and i-butanol) was as much as > 98% over [RhMo6O18(OH)(6)](3-)/FSM-16 catalysts and 73% over RhCl3/FSM-16 catalysts. Under the hydroformylation reaction conditions at 433 K and 60 kPa, 22-28 A of supported nanoparticles were present based on Rh K-edge extended X-ray absorption fine structure (EXAFS) and high-resolution transmission electron microscopy (HR TEM) measurements. Rh metallic nanoparticles atomically mixed with Mo atoms and distorted heteropolyacid species coexisted in the [RhMo6O18(OH)(6)](3-)/FSM-16 catalysts based on Rh and Mo K-edge EXAFS and HR TEM measurements. The population of metallic nanoparticles increased as the metal loading amount decreased from 5.2 to 0.22 wt % Rh. Thus, metallic nanoparticles in FSM-16 were essential for the butanol synthesis and Mo played an additional promoter role to increase the selectivity further. A reaction mechanism was proposed in which the metallic nanoparticle surface was predominantly adsorbed with CO and multiple-step hydrogenations of oxygenate intermediates proceeded to form butanols during slow diffusion in the two-dimensional mesoporous space.

Sn K alpha(1)-detecting Sn K-edge XANES spectrum was successfully measured for Pt-Sn/SiO2 catalyst (2.5 wt.% Pt, Sn/Pt atomic ratio 1.0) in the energy resolution 5.0 eV using Rowland-type fluorescence spectrometer equipped with Ge(13,13,13) bent crystal. The steeper, more clearly resolved XANES spectrum thus obtained could be compared quantitatively to theoretical XANES spectra generated by ab initio calculations for thirteen plausible Pt-Sn site models (alloy, adsorbed Sn, and mixture models). This spectral simulation suggested that fluorescence-detecting XANES is a simple method to judge the plausible site structure without detailed spectral analyses. The comparison supported an adsorbed Sn site model structure on highly dispersed Pt[-Sn] nanoparticles on SiO2. (C) 2006 Elsevier B.V. All rights reserved.

Ethanol photo-oxidation was investigated over mesoporous, amorphous V + TiO2 and V + TiO2(anatase) catalysts. Under the UV + visible light, mesoporous V + TiO2 generally exhibited faster photo-oxidation rates than V + TiO2(anatase) catalysts did. V-IV doping directed preferable formation of acetic acid rather than predominant acetaldehyde formation. Under the visible light only, mesoporous V-IV-TiO2 catalyst exhibited best reactivity among all V + TiO2 catalysts. Ethanol dehydration reaction was preferred. Initial quicker water evolution may suggest greater oxidation capability compared to V + TiO2(anatase) catalysts. (c) 2007 Elsevier B.V. All rights reserved.

A series of iron intercalated montmorillonites (Fe-Monts) were prepared using (i) ion exchange of native sodium and calcium ions with iron ions, (ii) base hydrolysis of inserted iron ions in montmorillonite suspension, and (iii) insertion of pre-hydrolyzed iron colloid in montmorillonite. The materials were characterized by X-ray diffraction and gas adsorption-desorption techniques. The basal d(001)-spacing and BET specific surface area increased after the intercalation of iron species in montmorillonite. Local iron structure studied by X-ray absorption fine structure (XAFS) spectroscopy showed an unsaturation of the Fe center dot center dot center dot Fe coordination number (N 2.5) of the intercalated iron species as compared to the bulk iron oxyhydroxides (N 6). The Fe-Monts were employed for arsenic removal from aqueous solutions at low concentration (0.2-16 mg/L). Among the Fe-Monts, the one prepared by the hydrolysis of inserted iron ions, was the best in performance. The saturation adsorption amount of the optimized iron-montmorillonite was 4 and 28 times higher for the removal of arsenite and arsenate, respectively, as compared to bulk iron oxyhydroxide (goethite). Compared with bulk iron oxyhydroxide, the Fe-Monts were superior for arsenate uptake and comparable for arsenite. In addition, arsenite adsorbed on the Fe-Monts was found to be oxidized to arsenate based on XAFS spectroscopy.

State-sensitive XAFS was enabled combined with high-energy-resolution (Delta E=0.3 eV@5.5 keV) X-ray fluorescence spectrometry and applied to Au sites of Au/TiO2 and Sn promoter sites of Pt-Sn/SiO2. Each state of interfacial Au sites located on Ti/O atoms and negatively/positively charged Au-n clusters was discriminated. Feasibility of more direct information of on-site catalysis via frontier orbital-sensitive XAFS was demonstrated.

The instability of inorganic framework has been the greatest barrier to synthesize micro and mesoporous Fe-III/II materials. This paper uses dodecylsulfate to organize lamellar-structure FeOx(OH)(y) composite followed by smaller carboxylates exchange (formate, acetate, or propionate) to create micropores. XRD, nitrogen sorption/desorption, HR-TEM, FT-IR, ICP, EPMA, TG-DTA, and Fe K-edge EXAFS measurements were used for the characterizations. The lamellar-structure reorganized to wormhole-like framework stabilized with carboxylate anions adsorbed inside micropores. Upon heating at 423 K, a half of acetates/propionates diminished and the specific surface area increased to as much as 230 m(2) g(-1). Based on the Fe K-edge EXAFS for FeOx(OH)(y) composite and derivative porous Fe-III materials, Fe-O bonds were observed at 2.04-2.09 angstrom with the coordination number 5-6. Farther Fe (...) Fe bonds also appeared at 3.21-3.25 angstrom. The coordination number was obtained to 2-3, reflecting higher dispersion and higher surface area for these porous Fe-III materials. The acetate-exchanged FeOx(OH)(y) heated at 423 K exhibited greatest saturated sorption amount (21 mg(As) g(adsorbent)(-1)) and equilibrium sorption constant (1.0 X 10(7) ml g(As)(-1)) angstrom. in 0.2-32 ppm of arsenite test solutions among other relevant Fe-III materials and Fe-III nanoparticles intercalated between clay layers. (c) 2006 Elsevier Inc. All rights reserved.

Direct observation of sulfur sites for sulfur-containing compounds (cysteine and its oxidative derivatives) on ferrite nanoparticles (FP) was performed by X-ray adsorption near edge structure (XANES) measurements. XANES spectra of cysteine derivatives conjugated with FP indicated that redox reactions occurred on the FP surface. Cysteine was completely oxidized to cystine and cysteinesulfinic acid and cysteic acid were partially reduced. These studies revealed that the FP surface should possess both an oxidation and reduction reactive center for sulfur-containing functional groups.

Crystalline powders of anhydrous MnV2O6 were successfully synthesized at a temperature below 200 degrees C under autogenous hydrothermal condition. MnV2O6 powders, which were synthesized using high concentration solutions, more than 0.1 mol/L, gave a relatively high reversible capacity of 600 mA h/g and interesting cyclic performance, reversible capacity increasing to more than an initial charge capacity after the 3rd or 4th cycle of charge-discharge. The change in oxidation state of V ion on the course of the 1st discharge-charge process was investigated by different techniques, such as XAFS and XPS. During discharging, V5+ was found to change gradually to V4+, but it returned back completely to V5+ on charging process. The thinner particles of MnV2O6 crystals with rod-like morphology were synthesized at 135 degrees C, and much better anodic performance was achieved, much smaller irreversible capacity as about 300 mA h/g, stable reversible capacity as 600 mA h/g, and 100% Coulombic efficiency. (c) 2006 Published by Elsevier B.V.

The sulfur K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy is applied to homoleptic thiolato complexes with Zn(II) and Cd(II), (Et4N)[Zn(SAd)(3)] (1), (Et4N)(2)[(Zn(ScHex)(2))(2)(mu-ScHex)(2)] (2), (Et4N)(2)[{Cd(ScHex)(2)}(2)(mu-ScHex)(2)] (3), (Et4N)(2)[{Cd(ScHex)}(4)(mu-ScHex)(6)] (4), [Zn(mu-SAd)(2)](n) (5), and [Cd(mu-SAd)(2)](n) (6) (HSAd = 1-adamantanethiol, HScHex = cyclohexanethiol). The EXAFS results are consistent with the X-ray crystal data of 1-4. The structures of 5 and 6, which have not been determined by X-ray crystallography, are proposed to be polynuclear structures on the basis of the sulfur K-edge EXAFS, far-IR spectra, and elemental analysis. Clear evidences of the S center dot center dot center dot S interactions (between bridging atoms or neighboring sulfur atoms) and the S center dot center dot center dot C-far interactions (in which C-far atom is next to carbon atom directly bonded to sulfur atom) were observed in the EXAFS data for all complexes and thus lead to the reliable determination of the structures of 5 and 6 in combination with conventional zinc K-edge EXAFS analysis for 5. This new methodology, sulfur K-edge EXAFS, could be applied for the structural determination of in vivo metalloproteins as well as inorganic compounds. (C) 2005 Elsevier Inc. All rights reserved.

X-ray absorption near-edge structure (XANES) suffers from core-hole lifetime broadening at a higher energy absorption edge, such as Sn K (29 keV, T-K = 8.49 eV). To overcome this problem, emitted Sn K alpha(1) fluorescence from sample was counted using high-energy-resolution fluorescence spectrometer in the XANES measurements. Experimental energy resolution (5.0 eV) was consistent with theoretical values based on the Rowland configuration of the spectrometer. The absorption edge became steeper compared to conventional spectra. The white-line peak due to Sun species became remarkably sharper and more intense in the Sn K alpha(1)-detecting Sn K-edge XANES for Pt-Sn/SiO2. To support the semiclassical theory of resonant Raman scattering for the explanation of observed elimination of lifetime width, more resolved XANES data at Cu K, Ph L-3, and Sn K in this work were convoluted (filtered) with a Lorentzian of each core-hole lifetime width. The processed data resembled generally well corresponding XANES spectrum measured in transmission mode. The verification based on ab initio XANES calculations was also performed.

X-ray absorption fine structure combined with X-ray fluorescence spectrometry was applied to various V+TiO2 hybrid samples. Emitted V Kα1f luorescence from the sample was selectively counted by using a high-energy-resolution (0.4 eV) spectrometer equipped with a Ge(331) crystal. Two advantages of this method, extremely high signal/background ratio and the compatibility of measurements in the atmosphere of reaction gas (in situ study in relation to heterogeneous catalysis), were effective at the V K-edge. Structure transformation of the V sites was spectroscopically followed for the V/TiO2 catalyst. The monooxo tetrahedral vanadate site was demonstrated to exist at 473 K. It transformed into dispersed species of 5-fold coordination in ambient air and further into polymeric VOx species in 0.85 kPa of water at 290 K. In the presence of 3.2 kPa of 2-propanol, dissociative adsorption of 2-propanol on the dispersed V species was strongly suggested at 290-473 K. In situ structure changes of V sites on TiO2 were reported by means of XAFS for the first time. The V(V) sites for the V/TiO2 catalysts were essentially identical with those for V supported on mesoporous (high-surface-area) TiO2 and V-TiO2 sample prepared by the sol-gel method. However, predominant V(IV) sites were found for mesoporous V-TiO2. The V(IV) sites substituted on the Ti sites of TiO2. When the molar ratio of V/Ti increased from 1/100 to 1/5.0, major octahedral V sites in the TiO2 matrix looked to transform into tetrahedral ones.

Vanadium monomers with chiral tridentate Schiff-base ligands were supported on SiO2 through a chemical reaction with surface silanols, where we found a new chirality creation by the self-dimerization of the vanadyl complexes on the surface. The chiral self-dimerization and the role of surface silanols in the self-assembly were investigated by means of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), diffuse-reflectance ultraviolet/visible (DR-UV/VIS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), electron spin resonance (ESR), and density functional theory (DFT) calculations. The surface vanadyl complexes had a distorted square-pyramidal conformation with a V=O bond. FT-IR spectra revealed that the Ph-O moiety of Schiff-base ligands was converted to Ph-OH by a surface-concerted reaction between the vanadium precursors and surface SiOH groups. The Ph-OH in an attached vanadyl complex interacted with a COO moiety of another vanadyl complex by hydrogen bonding to form a self-dimerized structure at the surface. The interatomic distance of V-V in the surface self-assembly was evaluated to be 0.40 +/- 0.05 nm by ESR after O-2 adsorption. The self-dimerized V structure on SiO2 was modeled by DFT calculations, which demonstrated that two vanadium monomers with Ph-OH linked together by two hydrogen bonds and their V=O groups were directed opposite to each other. The surface self-dimerization of the vanadium precursors fixes the direction of the V=O bond and the plane of the Schiff-base ligand. Thus, a new chiral reaction field was created by two types of chirality: the chiral Schiff-base ligand and the chiral V center. We have also found that the chiral self-dimerized vanadyl complexes exhibit remarkable catalytic performance for the asymmetric oxidative coupling of 2-naphthol: 96% conversion, 100% selectivity to 1;1 '-binaphthol (BINOL), and 90% enantiomeric excess (ee). Increasing the vanadium loading on SiO2 caused a dramatic swell of enantioselectivity, and the maximum 90% ee was observed on the supported catalyst with the full coverage of the vanadyl complex (3.4 wt % vanadium). This value is equivalent to the maximum ee reported in homogeneous catalysis for the coupling reaction. Furthermore, the supported vanadium dimers were reusable without loss of the catalytic performance. To our knowledge, this is the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol.

This paper first deals with the screening and optimization of Fe III-based adsorbents for arsenic adsorption from 0.2 to 16 ppm test solutions of arsenite/arsenate. The best adsorption capacity has been reported on α-FeO(OH) on an adsorbent weight basis. Better results were found on intercalated Fe-montmorillonites for arsenite adsorption below the equilibrium dissolved As concentration of 310 ppb and for arsenate adsorption in all of the concentrations studied. Next, the speciation of As adsorbed was performed by As K-edge x-ray absorption fine structure (XAFS) combined with high-energy- resolution fluorescence spectrometry. Major oxidative adsorption of arsenite was observed on Fe-montmorillonite from the 0.2-16 ppm test solutions. The reasons for the higher capacity of arsenic adsorption and oxidative adsorption of arsenite on Fe-montmorillonite are discussed. © 2005 American Chemical Society.

Insoluble clay-cerium hydroxide conjugates exhibiting only limited swelling in water were synthesized for the removal of arsenic ions from aqueous solution. Thus, cerium hydroxide was immobilized electrostatically on the inner layer of highly dispersed Na-montmorillonite (clay). The clay + Ce(OH)(n) conjugate was prepared by intercalating colloidal cerium hydroxide in the clay inner layer. Similarly, the clay + Ce -> OH conjugate was prepared by introducing cerium ions into the clay followed by their hydrolysis. The intercalation of cerium hydroxide and the chemical state of the cerium ion in the clay were evaluated via X-ray diffraction and X-ray absorption fine structure (XAFS) measurements. The conjugates exhibited a mesoporous structure with a high specific surface area of ca. 85-100 m(2)/g. These conjugates adsorbed As(III) and As(V) in a similar manner from aqueous solutions of As2O3 and KH2AsO4, respectively, over the pH range 4-8. The adsorption isotherms for As(III) and As(V) onto the conjugates were Langmuirian in shape. They exhibited large values for the Langmuir constant, K, thereby indicating the effectiveness of the conjugates in the removal of arsenic ions from dilute aqueous solutions. The adsorption capacity of the clay + Ce->OH conjugate was superior to that of the clay + Ce(OH)(n) conjugate. Co-existing anions in the aqueous solutions such as chloride, carbonate, sulphate and phosphate had little effect on the removal of arsenic.

X-ray absorption fine structure combined with fluorescence spectrometry was used for the speciation of trace amounts of lead and arsenic adsorbed. The Pb2+ species were effectively adsorbed on a layered material Mg 6Fe2(OH)16(CO3)•3H 2O from 100?ppb-1.0?ppm test aqueous solutions. A eutectic mixture of PbCO3 and Pb(OH)2 coagulated in the case of a 1.0?ppm Pb2+ solution, and in contrast, the major species was ion-exchanged Pb2+ in the case of the adsorption from the 100?ppb aqueous solution. The arsenic species were effectively adsorbed on intercalated Fe-montmorillonite from 50?ppb-16?ppm test aqueous solutions. In this concentration range, As3+ in the solution was oxidized upon adsorption. The adsorbed structure was suggested to be [AsV(OH) 2(μ-OFe)2] both in the cases of adsorption of As 3+ and As5+. © Physica Scripta 2005.

New spectroscopic tool to investigate the site structure of trace amounts of element in complex samples is introduced. The tool also selectively monitors the chemical state of an element by utilizing the chemical shift of each state. The experimental configuration of X-ray absorption fine structure combined with fluorescence spectrometry and the applications to trace amounts of lead and vanadium in heavy-element matrix and to chemical-state-selective measurements for copper catalyst are reviewed.

Selective XAFS measurements of 0.6-3.0wt% V sites on/in TiO2 were enabled utilizing a fluorescence spectrometer. The V sites were V-IV species in the case of high-surface-area V-TiO2 in contrast to V-V species in the case of conventional V/TiO2 catalysts, V supported on HSA-TiO2, and V-TiO2 prepared in the absence of dodecylamine (general sol-gel method).

The local structure of trace amounts of lead in an adsorbent matrix that contains a high concentration of iron and magnesium (Mg6Fe2(OH)(16)(CO3).3H(2)O) Was successfully monitored by means of X-ray absorption fine structure spectroscopy combined with fluorescence spectrometry. A eutectic mixture of PbCO3 and Pb(OH)(2) coagulated when Pb2+ was adsorbed from a 1.0 ppm aqueous solution, and in contrast, the major species was ion-exchanged Pb2+ in the case of adsorption from a 100 ppb aqueous solution. The difference was ascribed to the balance between,the precipitation equilibrium for coagulation and the rate of the ion exchange reaction with surface hydroxyl groups.

TiO2-supported ruthenium-metal particles were derived from an anionic hexanuclear carbido carbonyl cluster [Ru6C(CO)(16)](2-) and compared with those prepared conventionally by impregnation of TiO2 with a solution of RuCl3 followed by reduction with H-2. The average sizes of the metal particles in both systems are similar, that is, 12 Angstrom for molecular cluster-derived particles and 15 Angstrom for those derived from the RuCl3 precursor, although the size distribution is sharper in the former case. These supported particles efficiently promote the reduction of SO2 with H-2 to give elemental sulfur. Their active form is ruthenium sulfide as confirmed by EXAFS and X-ray diffraction measurements. The nanoscale ruthenium sulfide particles, which originated from the cluster complex, have an amorphous character and show activity even at low temperature (463 K), whereas ruthenium sulfide formed from RuCl3-derived metal dispersion is a pyrite-type RuS2 crystallite and needs a temperature above 513 K to effect the same catalysis. Amorphous ruthenium sulfide maintains its nano-sized scale (approximate to 14 Angstrom) regardless of the reaction temperature, while RuS2 crystallite aggregates to form larger nonuniform particles.

A trace amount of lead on adsorbent Mg6Fe2(OH)16(CO3)·3H2 O was selectively monitored by XAS combined with a fluorescence spectrometer. In the presence of dominant scattered and emitted X-rays derived from heavy elements (Fe and Mg), large quantities of heavy elements predominantly absorb the incident photons and the X-ray fluorescence derived from trace amounts of elements is very weak compared to scattered + emitted X-rays derived from heavy elements. Pb Lα1 emission was counted during XAS measurements with a fluorescence spectrometer of energy resolution of 1.1 eV. The obtained spectrum was compared to the spectra for standard Pb2+ compounds. The ion exchange mechanism FeO(OH) + Pb2+ → FeO-OPb+ + H+ was rejected, but a eutectic mixture of PbCO3 and Pb(OH)2 may be coagulated on the basic surface of adsorbent.

The preparation process of ruthenium carbido-cluster catalysts for the reduction of sulfur dioxide was traced by means of sulfur K-edge X-ray absorption near-edge structure (XANES). During the activation process, a pair of peaks at 2472.5 - 2472.8 and 2482.7 - 2482.8 eV appeared. The pair was ascribed to the M, phase. Once the catalysts were activated at 503 - 573 K, another pair of peaks at 2474.2 and 2479.2 eV appeared. The pair was assigned to the pi* and sigma* transition peaks, respectively, of adsorbed SO2 molecules on the catalyst surface.

The major local structure of low concentrations (1-3 wt% V) of vanadium on TiO2 was determined to have two terminal oxo groups and in total five oxygen coordination by means of vanadium K-edge XANES and ab initio calculations of XANES spectra.

To overcome the problem of X-ray absorption fine structure (XAFS) spectroscopy in which the obtained information is the average for all sites in sample, Rowland-type fluorescence spectrometer was designed to measure site-selective XAFS spectra by utilizing the chemical shift of emission peak for each site. Johansson-type cylindrically-bent Ge(111) crystal and scintillation counter were mounted on the spectrometer. The improvement of energy resolution of spectrometer was discussed when the primary beam size and two slit size in the Rowland circle were varied. The energy resolution was ∼1.1 eV, smaller than the core-hole lifetime width for Cu Kα1 (2.11 eV). The site selection of the Cu0 and CuI site-tune spectra was experimentally measured for the physical mixture of Cu metal+CuI and for Cu/ZnO catalyst. Obtained experimental site selection was compared to the theoretical estimations. © 2001 Elsevier Science B.V.

Simultaneous removal of nitrogen monoxide and dinitrogen oxide with propene was investigated over Pd-H-ZSM-5 catalysts. Results were compared with reports of simultaneous removal of NO and N2O in the presence of O-2 over Co-ZSM-5 and Fe-MFI. The N2O conversion was suppressed in the presence of NO, and the simultaneous removal rates were essentially the same as the NO conversion rates over Co-ZSM-5 and Fe-MFI. In contrast, the simultaneous removal in the presence of O-2 was found to be accelerated over Pd-H-ZSM-5 and conventional Pd/SiO2 compared to the sum of the corresponding individual removal rates of NO and N2O. An intense FT-IR peak of NO+/-0 ligated to the Pd cation inside the ZSM-5 cage was observed at 1868 cm(-1) in the promoted simultaneous removal reactions. Under the conditions for the individual removal of NO or N2O and the unpromoted simultaneous removal of NO + N2O, only a weak peak at 1842 cm(-1) was observed. The oxygen atom that dissociates from N2O should be the key to promoted catalysis in the coexistence of NO and N2O in order to maintain the Pd cation site clear. The oxygen controls the concentration of surface carbonaceous species to effectively decompose NO, and so as not to inhibit the NO activation.

XAFS (X-ray absorption fine structure) spectra were measured by using the fluorescence spectrometer for the emitted X-ray from sample. The chemical shifts between Cu-0 and Cu-I and between Cr-III and Cr-VI were evaluated. Tuning the fluorescence spectrometer to each energy, the Cu-0 and Cu-I site-selective XANES for Cu/ZnO catalyst were measured. The first one was similar to the XANES of Cu metal and the second one was the 5 : 5 average of XANES for Cu-I sites + Cu metal. The population ratio of copper site of the Cu/ZnO catalyst was found to be Cu metal : Cu2O : Cu-I atomically dispersed on surface = 70(+/-23) : 22(+/-14) : 8(+/-5). Site-selective XANES for Cr-III site of Cr/SiO2 catalyst was also studied.

A Rowland-type fluorescence spectrometer was designed to measure site-selective XAFS spectra by utilizing the chemical shift of emission peak for each site. The positions of Johansson-type cylindrically-bent Ge(111) crystal and scintillation counter were controlled independently by five-channel stepping motors, thereby satisfying precise Rowland condition. Thus, measurements of many fluorescence lines over wide ranges of Bragg angle 55.6-83.9° and Rowland radius 127.7-240.9 mm are made feasible. The Cu Ka peak shifted by +1.6 eV on going from Cu to CuCl and by -0.6 eV on going from CuCl to CuCl2. The CrKβ 1 peak shifted by +0.8 eV on going from Cr to Cr 2O 3 and by -1.6 eV on going from Cr 2O 3 to K 2CrO 4. The FWHM of Cu Kα peaks was as small as 3.0 eV. The major factor to control the energy resolution of this spectrometer was found to be geometrical angle width (slit size). The effects of Rowland radius and X-ray penetration depth into the bent crystal were smaller in the range of slit size in this paper [slit length (horizontal) in front of I 0 ion chamber was 0.5-2.0 mm and two slit lengths (vertical) in Rowland circle were 0.5-5.5 mm].

Site-selective XAFS spectra were measured by tuning the Rowland-type fluorescence spectrometer to each site of Cu/ZnO and Cr/SiO2 catalysts. The chemical shifts between Cu0 and Cu(I) sites and between Cr(III) and Cr(VI) sites were relatively large for model compounds (ΔE = 1.6 eV), and were utilized as the tune energies of site-selective XAFS. Site-selective XANES tuned to Cu0, Cu(I), and Cr(III) sites were successfully obtained. Based on the correlation between the chemical shift and the peak width (energy resolution of the fluorescence spectrometer), site-selective XANES spectra were analyzed. The population ratio of Cu metal, Cu2O, and Cu(I) atomically dispersed on ZnO was estimated to be 70(±23):22(±14):8(±5). The contribution of the Cr(III) site to site-selective XANES tuned to the Cr(III) site was 94(±3)%.

The design and performance of the high-brilliance XAFS facility at BL10XU of SPring-8, aimed at rapid and sensitive measurement of X-ray absorption fine structure (XAFS), is reported. Both undulator gap and double-crystal monochromator have been successfully controlled covering a wide energy range (5-30 keV). A versatile goniometer system, consisting of two independent high-precision goniometers. is capable of polarized XAFS in fluorescence mode and surface-sensitive experiments using a grazing-incidence geometry. By sharing major components, i.e. a monolithic Ge 100-pixel array detector and a closed-cycle He cryostat, both polarized XAFS and X-ray standing wave (XSW) experiments can be performed at low temperature (15-300 K). The performance of the spectrometer has been evaluated by recording XAFS spectra in transmission mode.

The structure of sol-gel Mo-SiO2 catalysts was investigated by Mo K-edge XAFS. The analysis demonstrated distorted Tdcoordination of two oxo groups (1.68A) and two oxygen atoms (1.93Å) around the Mo atom. The two oxo groups terminate the silica framework, thereby exposing the Mo site at surface. The XAFS spectra did not change upon reduction to Movby carbon monoxide except for the red-shift of XANES suggesting the participation of surface O atoms in the oxidation reaction. Up to two nitrous oxide molecules were found to adsorb on one Mo site at 293K, and to decompose to form O radical and nitrogen gas at 373 K. These results were supported by molecular orbital calculations for standard Mo compounds and model Mo sites of the sol-gel Mo-SiO2 catalysts.

A contracted Ni2+ coordination site distorted in the direction of Ni ... Mg and Ni ... Ni was found to be responsible for catalytic N2O decomposition when Ni2+ is diluted in a MgO matrix (Ni2+/Mg2+ atomic ratio approximate to 1.0) based on a local structure study by nickel K-edge X-ray absorption fine structure spectroscopy.

X-ray absorption spectra have been measured at the S K-, Cl K-, and Mo L-3- and L-2-edges for the d(0) dioxomolybdenum(VI) complexes LMoO2(SCH2Ph), LMoO2Cl, and LMoO2(OPh) (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) to investigate ligand-metal covalency and its effects on oxo transfer reactivity. Two dominant peaks are observed at the S K-edge (2470.5 and 2472.5 eV) for LMoO2(SCH2Ph) and at the Cl K-edge (2821.9 and 2824.2 eV) for LMoO2Cl, demonstrating two major covalent contributions from S and Cl to the Mo d orbitals. Density functional calculations were performed on models of the three Mo complexes, and the energies and characters of the Mo 4d orbitals were interpreted in terms of the effects of two strong cis-oxo bonds and additional perturbations due to the thiolate, chloride, or alkoxide ligand. The major perturbation effects are for thiolate and Cl- pi mixed with the d(xz) orbital and sigma mixed with the d(z)(2) orbital. The calculated 4d orbital energy splittings for models of these two major contributions to the bonding of thiolate and Cl ligands (2.47 and 2.71 eV, respectively) correspond to the splittings observed experimentally for the two dominant ligand K-edge peaks for LMoO2(SCH2Ph) and LMoO2Cl (2.0 and 2.3 eV, respectively) after consideration of final state electronic relaxation. Quantification of the S and Cl covalencies in the d orbital manifold from the pre-edge intensity yields, similar to 42% and similar to 17% for LMoO2(SCH2Ph) and LMoO2Cl respectively. The Mo L-2-edge spectra provide a direct probe of metal 4d character for the three Mo complexes. The spectra contain a strong, broad peak and two additional sharp peaks at higher energy, which are assigned to 2p transitions to the overlapping t(2g) set and to the d(z)(2) and d(xy) levels, respectively. The total peak intensities of the Mo L-2-edges for LMoO2(OPh) and LMoO2Cl are similar to and larger than those for LMoO2(SCH2Ph), which agrees with the calculated trend in ligand-metal covalency. The theoretical and experimental description of bonding developed from these studies provides insight into the relationship of electronic structure to the oxo transfer chemistry observed for the LMoO2X complexes. These results imply that anisotropic covalency of the Mo-S-cys bond in sulfite oxidase may promote preferential transfer of one of the oxo groups during catalysis.

We describe the design and performance of a high-brilliance XAFS station at BL10XU of SPring-8 planned for rapid and sensitive Xray absorption fine structure (XAFS). A deflection parameter K-y of undulator and a double crystal monochromator have been successfully tuned to cover a wide range in energy (5-30 keV). For a high throughput fluorescence data acquisition, a 100-pixel Ge detector has been developed which allows a total count rate exceeding 30 MHz with a typical energy resolution of 270 eV at 5.9 keV. A three-axis high-precision goniometer is designed to provide any polarization geometry including a grazing-incidence fluorescence excitation.