Tetsuhiko Kobayashi

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

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Publications (95)208.83 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A simple and highly efficient surfactant-free sol–gel process has been developed to obtain nanocrystalline mesoporous γ-Al2O3 and metal ion incorporated mesoporous γ-Al2O3 with general formula γ-Al2−xMxO3±y (where M = Ti4+ through Ga3+). Any one of the first row transition metal (TM) ions along with Ga3+ could be introduced into the γ-Al2O3 framework in a direct one-pot synthesis process. The generality of the present synthesis recipe for metal ion incorporation in γ-Al2O3 was demonstrated by preparation of an Al–Ga–M ternary oxide system with the metal ion composition of general formula Al9GaTM (TM = Ti4+ to Zn2+) and their characterization through various physicochemical and spectroscopic techniques. The mesoporous γ-Al2−xMxO3±y materials showed a BET surface area in the range of 200–400 m2 g−1 with a narrow pore size distribution. Wormhole mesoporosity makes the material pseudo-3D (p3D) with a small pore depth of few nm (<10 nm). Metal ions in γ-Al2O3 lead to changes in the acidity and electronic environment. XRD, TEM, and 27Al MAS NMR studies demonstrate that the sol–gel process and the disordered mesoporous structure allow Ga and TM ions to be highly distributed and integrated in the γ-Al2O3 framework. The efficacy of these materials in catalysis has been successfully evaluated for steam reforming of dimethylether: Ni, Cu and Zn containing Al9GaTM oxides showed high activity and stability. The smaller mesochannel depth (<10 nm) and pseudo-3D characteristics that arise due to the wormhole-type disordered mesoporous framework of these alumina materials facilitate mass transport through them without any leaching of metal ions out of the lattice and pore blocking during the reaction, which makes them attractive in catalysis. This preparation method is versatile enough to be used for a reproducible synthesis of metal ion incorporated mesoporous γ-Al2O3 by varying the metal content and their combinations, and it is expected that many other metal ions could be introduced into the lattice framework for a variety of applications by tuning acidity and electronic structure.
    Journal of Materials Chemistry 06/2012; 22(27):13484-13493. · 6.63 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 32(39).
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    ABSTRACT: A study has been undertaken on the thermal stability and dispersion behavior of nanostructured CexZr1−xO2 mixed oxides over anatase-TiO2 support, synthesized by a deposition coprecipitation method and subjected to heat treatments at different temperatures. An unsupported CexZr1−xO2 mixed oxide was also synthesized by coprecipitation method for the purpose of comparison. The structural/morphological characterization was performed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature-programmed reduction (TPR) techniques. XRD measurements revealed the presence of cubic Ce0.75Zr0.25O2 phase at 773 K and incorporation of more zirconium into the ceria lattice at higher temperatures. HREM analysis conformed highly dispersed Ce−Zr nano-oxides over anatase-TiO2 support having the sizes in the range of 3−5 nm at 773 K. At higher temperatures, a slight increase in the crystallite size (5−10 nm) has been observed. The XPS measurements revealed the stabilization of Ce3+ at higher temperatures and presence of Zr and Ti in 4+ oxidation states. UV−vis DRS studies showed that oxygen to metal (Ce4+/Ce3+) charge-transfer transitions occur at lower wavelengths in the case of CexZr1−xO2/TiO2 compared to pure CexZr1−xO2. TPR experiments revealed that the surface reduction of CexZr1−xO2/TiO2 takes place at lower temperatures, which facilitates better CO oxidation activity in comparison to the unsupported CexZr1−xO2.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2009; 48(1):453-462.
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    ABSTRACT: The electrochemical behavior of ammonia borane on an Au electrode in the absence and presence of thiourea (TU) was detailedly investigated by cyclic voltammetry (CV). In the absence of TU, the feature of the CV is fairly complex affected by both the hydrolysis and the direct oxidation of ammonia borane. With the aid of TU, known as an effective inhibitor for the formation and recombination of adsorbed H radicals associated with ammonia borane hydrolysis, the two peaks at 414 and 0mV may be attributed to direct electrooxidation of ammonia borane at Au electrode. These two peaks are particularly important for the practical direct ammonia borane fuel cell (DABFC). Additionally, the Tafel slope (b=0.15V) and charge transfer coefficient (α=0.604) were obtained as well as number of electrons exchanged (n=2) in the ammonia borane oxidation at the Au/solution interface in the presence of TU.
    International Journal of Hydrogen Energy - INT J HYDROGEN ENERG. 01/2009; 34(1):174-179.
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    ABSTRACT: Structural characteristics and catalytic activity of nanosized ceria−terbia mixed oxides have been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy, temperature-programmed reduction/oxidation, and Brunauer−Emmett−Teller surface area techniques. The catalytic usefulness has been evaluated for oxygen storage-release capacity (OSC) and CO oxidation activity. The XRD and TEM results suggest that the crystallite sizes of these nano-oxides are in the range 5−12 nm within the investigated temperature range of 773−1073 K. The mixed oxide solid solutions adopted a fluorite-type structure and exhibited cell parameters with respect to Vegard’s rule. The XPS measurements revealed that both cerium and terbium are in 3+ and 4+ oxidation states, 4+ being dominant in both cases. The reduction temperature of the Ce−Tb oxide is observed to be lower than that of the pure ceria and exhibited better redox properties due to the formation of solid solution. The OSC is substantially higher for the mixed oxide, and the presence of oxygen vacancies favored better CO oxidation activity. The nanosized ceria−terbia mixed oxide is also found to be thermally quite stable and capable of manifesting redox behavior after severe heat treatment.
    Journal of Physical Chemistry C - J PHYS CHEM C. 09/2008; 112(42).
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    ABSTRACT: In the LaFePdO3 perovskite catalyst, redox fluctuations of the exhaust gas suppress the growth of particles of precious metal by causing Pd to move in and out of the perovskite crystal. To observe the real movements of Pd directly, the time evolution of local structure around Pd by redox fluctuations was investigated by in situ energy-dispersive X-ray absorption fine-structure (DXAFS) analysis with a 10ms resolution. We proved that the change in structure of Pd is sufficiently fast to respond to the control frequency (1–4Hz) of an actual gasoline engine and that the Pd particles that segregate out are extremely fine.
    Catalysis Communications - CATAL COMMUN. 01/2008; 9(2):311-314.
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    ABSTRACT: Mesoporous and worm-like In2O3 catalysts have been prepared using KIT-6 and MCM-41 silicas as templates, which show low crystallinities and high surface areas. Compared with commercial In2O3 catalyst with low surface area, these two nano-structured In2O3 catalysts exhibit higher catalytic activity for steam reforming of ethyl alcohol at low temperature to produce hydrogen containing no detectable CO impurity, presenting an advantage in comparison with the previous reported catalysts.
    Journal of Power Sources 01/2008; 179(2):566-570. · 5.26 Impact Factor
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    ABSTRACT: The crystal structures, electronic, dielectric, and vibrational properties of NaH, Na(2)O and NaOH are systematically investigated by first-principles calculations and the quasiharmonic approximation. The phonon dispersion relations and the phonon density of states of the phases and their thermodynamic functions including the heat capacity, the vibrational enthalpy, and the vibrational entropy are calculated using a direct force-constant method. Based on these results, the dehydrogenation reaction, NaH+NaOH-->H(2)+Na(2)O, is predicted to take place at 528 K, which is in agreement with the experimental observed value.
    ChemPhysChem 09/2007; 8(13):1979-87. · 3.35 Impact Factor
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    ABSTRACT: Ammonia-borane (NH3BH3), as a source of protide (H−), is initially proposed to release its energy through a fuel cell (direct ammonia-borane fuel cell, DABFC). Cell performance has been elucidated in a 25cm2 laboratory cell constructed with an oxygen cathode and an ammonia-borane solution fed anode, where the catalyst layers are made of Vulcan XC-72 with 30wt.% Pt. The potential is 0.6V at the current density of 24mAcm−2, corresponding to power density >14mWcm−2 at room temperature. The direct electron transfer from protide (H−) in NH3BH3 to proton (H+) has been further proved by the open circuit potential and the cyclic voltammetry results, which show the possibility of improvement in the performance of DABFC by, for example, exploring new electrode materials.
    Journal of Power Sources 05/2007; 168(1):167-171. · 5.26 Impact Factor
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    ABSTRACT: The adsorption and dissociation of H2 on the Na2O (110) surface have been studied with the first-principles molecular dynamics method. It is found that the adsorption configuration is energetically preferred when the H2 molecule is situated at the bridge site of the Na and O atoms, which indicates the formation of a Na−Hδ-···Hδ‘+−O dihydrogen bond, as confirmed by the charge distribution features and bond lengths between the concerned atoms. The molecular dynamics simulations reveal the dissociation of the newly discovered H···H dihydrogen bond, which facilitates the Na2O + H2 → NaH + NaOH reaction.
    Journal of Physical Chemistry C - J PHYS CHEM C. 03/2007; 111(13).
  • Angewandte Chemie International Edition 02/2007; 46(42):8024-7. · 11.34 Impact Factor
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    ABSTRACT: A comparative study on the effects of alkali metal on the structures, physico-chemical properties and catalytic behaviors of silica-supported vanadium catalysts for the selective oxidation of ethane and the complete oxidation of diesel soot was reported.
    Topics in Catalysis 07/2006; 38(4):309-325. · 2.61 Impact Factor
  • Angewandte Chemie International Edition 06/2006; 45(19):3120-2. · 11.34 Impact Factor
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    ABSTRACT: The thermal stability of a nanosized Ce(x)Zr(1-x)O2 solid solution on a silica surface and the dispersion behavior of V2O5 over Ce(x)Zr(1-x)O2/SiO2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VOx/Ce(x)Zr(1-x)O2/SiO2 catalyst. Ce(x)Zr(1-x)O2/SiO2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V2O5 was impregnated over the calcined Ce(x)Zr(1-x)O2/SiO2 sample (773 K) by an aqueous wet impregnation technique. The prepared V2O5/Ce(x)Zr(1-x)O2/SiO2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce0.75Zr0.25O2 in the case of Ce(x)Zr(1-x)O2/SiO2, while cubic Ce0.5Zr0.5O2 and tetragonal Ce0.16Zr0.84O2 in the case of V2O5/Ce(x)Zr(1-x)O2/SiO2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO4. The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of approximately 5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce(x)Zr(1-x)O2/SiO2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce(x)Zr(1-x)O2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.
    The Journal of Physical Chemistry B 06/2006; 110(18):9140-7. · 3.61 Impact Factor
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    ABSTRACT: The effects of various supports on the catalytic activity of Ga2O3 for the steam reforming of DME have been examined. Among the various supported Ga2O3 catalysts, Ga2O3/TiO2 showed the highest DME steam reforming activity in terms of DME conversion and H2 yield. The results from XRD, surface area and XPS indicate that the dispersion of Ga2O3 strongly depends on the catalyst support. A correlation between the XPS results and the DME steam reforming activity reveals that there is some electronic interaction between Ga2O3 and the support element. The large electronic interaction found in Ga2O3/TiO2 leads to the best catalytic performance among all the catalysts.
    Applied Catalysis A General 01/2006; 300(1):58-66. · 3.41 Impact Factor
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    ABSTRACT: Novel catalysts for dimethyl ether (DME) steam reforming (SR) were designed based on catalysis database on-demand. A catalyst library consisting of precious metals loaded on various metal oxides was tested for DME SR and its elemental reactions of DME hydrolysis and MeOH SR. Platinum loaded on alumina, Pt/Al2O3, shows high activity for DME SR as reported previously. The drawback of the catalyst was also confirmed; the formation of methane leading to the reduction of hydrogen formation. From the fact database for DME hydrolysis and MeOH SR built up with high-throughput experimentation tools, the high activity of Pt/Al2O3 for DME SR is owing to its high activity on DME hydrolysis because its activity on MeOH steam reforming is not remarkable. Based on these facts, novel catalysts were designed and achieved by physical mixing of Pt/Al2O3 which reveals high activity on DME hydrolysis with an active catalyst on MeOH steam reforming. By mixing of Pt/Al2O3 with Pd/Al2O3, methane formation was suppressed without loss of hydrogen production activity.
    Applied Surface Science 01/2006; · 2.54 Impact Factor
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    ABSTRACT: To lower Pt loadings for proton exchange membrane fuel cells (PEMFCs), electrocatalytic activity per unit mass of Pt should be improved. In this paper, we report that carbon black treated using C2F6 radio frequency plasmas is a good electrocatalyst support for the membrane electrode assembly of a PEMFC. The hydrophobicity of the catalyst support and the affected electronic state of the supported Pt particles, both of which are due to the introduced CF3 group, are thought to enhance the catalytic activity.
    Journal of Power Sources 01/2006; 161(2):836-838. · 5.26 Impact Factor
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    ABSTRACT: Sodium oxide, Na2O, reversibly absorbs hydrogen, H2, to form sodium hydride, NaH, and sodium hydroxide, NaOH, which possesses a potential to find its application to reversible hydrogen storage. X-ray diffraction measurements illustrate reversible phase and composition changes during the hydrogen absorption and desorption in the Na–O–H system. Pressure–composition (P–C) isotherm and thermogravimetric (TG) measurements exhibit a hydrogen capacity up to 3.0wt.%. Temperature-programmed desorption (TPD) measurements demonstrate that mixing NaOH to NaH significantly shifts the hydrogen desorption of NaH towards lower temperature, to which TiCl3 and SiO2 show catalytic activity. A reaction intermediate, NaHδ−⋯Hδ′+ONa, involving dihydrogen bonding between the negatively charged hydrogen atom bonded to sodium and the positively charged hydrogen atom bonded to oxygen is proposed for the reaction mechanism.
    Journal of Power Sources 01/2006; 155(2):167-171. · 5.26 Impact Factor
  • Yusuke Yamada, Tetsuhiko Kobayashi
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
    ChemInform 01/2006; 37(38).
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    ABSTRACT: Cyclohexene epoxidation with H2O2 was performed over RuO2/TiO2 under various conditions. The support TiO2 prepared by surfactant-assisted templating sol–gel method is nanocrystalline and has mesoporous structure with narrow monomodal pore size distribution. An activator of 1mol% RuO2 was loaded onto the synthesized TiO2 by incipient wetness impregnation method. The resultant catalyst was characterized by XRD, N2 adsorption–desorption and TEM analyses. Reaction conditions in the epoxidation reaction, namely reaction temperature, amount of catalyst and concentration of H2O2 in terms of cyclohexene/H2O2 ratio, were systematically optimized to obtain maximum selectivity to cyclohexene oxide.
    Journal of Molecular Catalysis A-chemical - J MOL CATAL A-CHEM. 01/2006; 248(1):226-232.

Publication Stats

502 Citations
208.83 Total Impact Points

Institutions

  • 2001–2012
    • National Institute of Advanced Industrial Science and Technology
      • Research Institute for Ubiquitous Energy Devices
      Tsukuba, Ibaraki, Japan
  • 1998–2010
    • Kansai University
      • Department of Chemistry and Materials Engineering
      Suika, Ōsaka, Japan
  • 2007
    • Daihatsu Motor Co., Ltd.
      Ōsaka, Ōsaka, Japan
  • 2002
    • University of Tsukuba
      Tsukuba, Ibaraki, Japan