Hiroshi Nakanishi

Osaka University, Suika, Ōsaka, Japan

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Publications (144)203.5 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Platinum is commonly used as a catalyst for the oxidation of NO in exhaust gas purification systems. However, in addition to its high cost, the intrinsic NO + O → NO2 reaction is endothermic and the rate-limiting O2,gas dissociative adsorption is activated on Pt(111). In this paper, we show for the first time that the pseudomorphic Pt monolayer on 3d transition metals promotes a thermodynamically and kinetically favorable NO oxidation compared to pure Pt. Using density functional theory-based first principles calculations, we show that such results are attributed to the weaker binding of O and NO on the bimetallic surfaces and the change of the binding configuration of NO2 into a structure that promotes easier N–O bond formation. These results provide insights into the design of low-cost and efficient catalysts for NO oxidation.
    Catal. Sci. Technol. 10/2014;
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    ABSTRACT: doi: 10.1021/jp507534f
    The Journal of Physical Chemistry C 10/2014; · 4.84 Impact Factor
  • Journal of Alloys and Compounds 05/2014; 594:93–101. · 2.73 Impact Factor
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    ABSTRACT: We investigated the reactivity of CeO2-supported Pt4 cluster (denoted as Pt4/CeO2(1 1 1)) toward O2 adsorption and dissociation as well as the geometry/electronic properties associated with such metal oxide supported cluster system using density functional theory and on-site Coulomb interaction correction via the Hubbard-like term, U (DFT+U). It was found that Pt4 binds strongly to CeO2(1 1 1) via Pt 2 2 4 2 2 2 4 2
    Applied Surface Science 01/2014; 288:244–250. · 2.54 Impact Factor
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    ABSTRACT: The absorption of H atom in H-covered Pd(110) (1 × 2) missing-row surface is investigated using density functional theory based calculations. For 1.5 monolayer H coverage, interaction among the adsorbed H atoms is found to be negligible and was verified by analyzing the electronic structure of the system and by comparing the calculated binding energies with low H coverage case. Neither the monoatomic absorption of H nor the assistance from the initially adsorbed H atom explains the experimentally observed presence of subsurface H in Pd(110) at high H coverage. Instead, H absorption is realized through the assistance of incoming H atoms from vacuum. The absorption of H in the H-covered surface is non-activated while the dissociation of H2 is the rate-limiting process. Dissociation on ridge site is energetically more preferred than on trough site and the difference in the activation barrier is elucidated by investigating the electronic structures of the system.
    International Journal of Hydrogen Energy 01/2014; 39(12):6598–6603. · 3.55 Impact Factor
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    ABSTRACT: Structures of deuterium (D) adsorbed on germanium (001) surface were studied by the density functional theory (DFT) calculations and by the scanning tunneling microscope (STM). Two structures of dihydride adsorption were identified on the Ge (001) surface by STM measurements and confirmed by DFT calculated topographies. Also, differences in structural stabilities were explained based on binding strength differences with Ge and on hybridization effect of the s-orbital of D with the Ge p states. The excitation mode of 0.18 eV observed in the STM dI/dV spectrum was found to correspond to the DFT calculated D-Ge stretching vibration mode of 0.17 eV.
    Journal of Applied Physics 01/2013; 113(2). · 2.21 Impact Factor
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    ABSTRACT: We investigated the ortho–para (o–p) H2 conversion on the O2/Ag(111) system, combining first principles calculations based on spin-polarized density functional theory with perturbative calculations. In this study, we calculated the o–p H2 conversion rate, using the standard Fermi's Golden Rule and compared the contribution efficacy of the magnetic dipole interaction and the Fermi contact interaction. The calculated o–p H2 conversion times induced by the magnetic dipole interaction and by the Fermi contact interaction, corresponding to the reciprocal of the o–p H2 conversion rates, are in the orders of 100–103 s and 100–106 s, respectively. In comparison with the o–p H2 conversion time of 610 s on clean Ag surfaces, these results indicate that the magnetic dipole interaction and the Fermi contact interaction enhance the o–p H2 conversion in the vicinity of O2. In addition, the magnetic dipole interaction and the Fermi contact interaction can be separately observed with the different distances between H2 and O2.
    Current Applied Physics 12/2012; 12:S115–S118. · 2.03 Impact Factor
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    ABSTRACT: NO oxidation reaction on the Pt cluster supported on γ-Al2O3(111) surface is investigated using the climbing image nudged elastic band (CI-NEB) calculation based on the density functional theory. This is to verify the possibility of using Pt-based catalyst for NO oxidation reaction which is the rate-limiting step for the NOx oxidation reaction. From investigations of NO adsorption and NO2 desorption on the Pt cluster supported on γ-Al2O3 (111) surface where the dissociated O atoms already formed and lie on the Pt cluster sites, we find the process requires no activation barrier. Furthermore, we also performed the first principles of molecular dynamics simulation to investigate NO oxidation reaction at certain range temperatures (400 K, 600 K and 800 K) for complement of CI-NEB calculation. From the results, we discussed the temperature dependence of NO oxidation reaction.
    Current Applied Physics 12/2012; 12:S110–S114. · 2.03 Impact Factor
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    ABSTRACT: Electron transport through the melamine molecule was studied. Melamine molecules adsorbed on a Cu(100) surface were investigated by density functional theory (DFT) calculations with the dynamical matrix method. On the basis of calculation results, a model Hamiltonian for a system composed of scanning tunneling microscope (STM), a melamine molecule, and a Cu surface was proposed, taking into account electron--vibron (electron--molecular vibrations) interactions within the melamine molecule. Then, the electronic current was formulated by the nonequilibrium Green's function (NEGF) method. Results show that current is affected by the electron--vibron interactions defined in the melamine molecule through its controllable structural changes. The rectification and fluctuation of current are triggered by low-energy electron--vibron interactions. Furthermore, the electron--vibron interaction effect is found to be enhanced as temperature increases to where higher-energy vibrons begin to be excited at lower energies. However, current becomes uniform at higher temperatures, which shows an undesired sensitivity. The weakening of the electron--vibron interaction of the out-of-molecular-plane vibrational motion can transfer the melamine molecule in its tautomerization state into a current rectifier. The reduction or induction of the repulsion of lone pairs of consecutive N atoms causes the induction or reduction of the low-energy in-plane vibrational motion, which in turn causes the switching of the I--V characteristics between less stable melamine tautomers.
    Journal of the Physical Society of Japan 10/2012; 81(10):4711-. · 2.09 Impact Factor
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    ABSTRACT: We present the results of density functional theory calculation in oxygen dissociative adsorption process on two types of isolated platinum (Pt) clusters: Pt4 and Pt10, by taking into account the effect of cluster reconstruction. The strength of Pt--Pt bonds in the clusters is mainly defined by d--d hybridization and interstitial bonding orbitals (IBO). Oxygen that adsorbed on the clusters is weakening the IBO and thus inducing geometry reconstruction as occurred in Pt10 cluster. However, cluster that could undergo structural deformation is found to promote oxygen dissociation with no energy barrier. The details show that maintaining well-balanced of attractive and repulsive (Hellmann--Feynman) forces between atoms is considered to be the main key to avoid any considerable rise of energy barrier. Furthermore, a modest energy barrier that gained in Pt4 cluster is presumed to be originate from inequality of intramolecular forces between atoms.
    Japanese Journal of Applied Physics 03/2012; 51(3):5002-. · 1.07 Impact Factor
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    ABSTRACT: Oxygen vacancy effect on the electronic state of Pt/NiO/Pt capacitor-like system is theoretically investigated by density functional theory (DFT) based first-principles calculations. The potential energy profile for electrons at the interface between Pt and NiO is found to play a major role on the transport properties alternations where conduction path begin to construct. Oxygen vacancies effect is summarized in the induction of a spatially localized spin-polarized state near the Fermi level of the surrounding Ni ions. Also, electron transport through O vacancy filaments (conduction paths) is via s-orbital sub-bands. We have found that the absence or presence of a vacancy near the interface at the edges of the vacancy filament causes a conductance jump from ~0 to 1e2/h respectively which corresponds to clearly observable switching.
    Surface Science 02/2012; · 1.87 Impact Factor
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    ABSTRACT: We have investigated the H2 molecular adsorption on the Ag(111) surfaces. To treat van der Waals (vdW) interaction accurately, we performed first principles calculation based on spin-polarized density functional theory (DFT) with the semiempirical correction term of vdW interaction. We got the value of 36.0 meV as the depth of potential energy with this method. We also found that in-plane diffusion barrier was less than 1.3 meV, and zero-point energy about perpendicular direction to the surfaces was 5.0 meV. Totally, the adsorption energy of H2/Ag(111) was 31.0 meV, which accordingly agreed with experimental value of 25.5 meV. We also calculated the ortho-para H2 conversion rate with the anisotropic potential energy. We found that this anisotropy induced the hindered rotational state, which imposed steric effects and accelerated ortho-para H2 conversion.
    Journal of the Vacuum Society of Japan 01/2012; 55(3):115-117.
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    ABSTRACT: We focused on the basic adsorption properties of two types of cations, viz., 1-methoxymethyl-1-methylpyrrolidinium (MMMP) and 1-ethyl-3-methylimldazolium (EMI), on graphene, as a first step in investigating the properties of carbon electrodes in an electric double layer capacitor. To clarify the basic adsorption properties, we used first principles calculation based on the density functional theory with the generalized gradient approximation for the exchange-correlation energy. We investigated the electrical dipole moment formed between the cations and graphene and found that electric dipole moment per cation formed by MMMP is larger than by EMI. In addition, we found that intramolecular bindings of MMMP are stronger than those of EMI. Based on these results, we conclude that MMMP is more suitable as the material for electric double layer capacitor than EMI.
    Journal of the Vacuum Society of Japan 01/2012; 55(4):198-203.
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    ABSTRACT: We have investigated the dissociative adsorption process of O2 (oxygen molecule) on a composite surface formed by coating a single platinum (Pt) adatom on a gamma-alumina (gamma-Al2O3) (111) surface. This process is studied by using density functional theory (DFT) and described in terms of potential energy surfaces (PES) with respect to the molecular degrees of freedom. We compare the activation barriers and adsorption energies among typical reaction channels. Our results show that O2 dissociative adsorption is preferably occurred when this O2 molecule approaches the surface with molecular orientation inclined by 30° angle with respect to the surface normal, i.e., the condition with lowest activation barrier. The results indicate that dissociated O atoms are likely to form strong bonds with the Pt adatom by keeping distance from the alumina layer.
    Japanese Journal of Applied Physics 10/2011; 50. · 1.07 Impact Factor
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    ABSTRACT: Hydrazine (N2H4) adsorption on metal surface is important due to its application in the direct hydrazine fuel cell technology. First principles DFT calculations have been carried out to understand the structure and mechanism of hydrazine adsorption on Pt(111). Calculations revealed that configuration with hydrazine adsorbed on its anti-conformation yields the largest adsorption energy suggesting it to be the most stable structure on Pt(111). This result was found to be in disagreement with available XPS results which favor the adsorption on cis-conformation as the most stable configuration. However, by taking into account the energy cost for orbital re-hybridization and internal rotation involves in the adsorption, it was found that the interaction strength between adsorbate and substrate is comparably equal for adsorption on both anti and cis-conformations that indicates the feasibility of the adsorption in cis-conformation to occur. Charge transfers from lone-pair orbitals belong to the highest occupied molecular orbital (HOMO) and second highest occupied molecular orbital (S-HOMO) were found to be important in the formation of the bonding. The π-anti-bonding HOMO lone-pair transfers its charge to the surface which stabilizes the internal structure of the molecule and responsible for the stable anti-conformation adsorption structure. The interaction of the π-bonding S-HOMO lone pair with the surface was found to be dative type and plays an important role in the stabilization of cis-conformation adsorption structure.
    Surface Science 08/2011; 605(15-16):1347-1353. · 1.87 Impact Factor
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    ABSTRACT: The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt4) clusters supported on gamma alumina (gamma-Al2O3) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt4 geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt4 on gamma-Al2O3 (111) surface in tetrahedron configuration is energetically more favorable as compared to that of the planar rhombus. However, it was found that NO molecule adheres strongly to Pt4 with planar configuration on gamma-Al2O3(111) surface. In addition, the NO adsorption calculation on the isolated Pt4 clusters also shows similar preference to planar configuration. The local density of states (LDOS) reveals that the difference in reactivity comes from the different hybridization strengths between the electronic states of nitrogen atom and those of platinum tetramers. The results are in good agreement with the experiments which show similar tendency for CO and N2O reactivity to gas-phase platinum clusters.
    Journal of Nanoscience and Nanotechnology 04/2011; 11(4):2844-50. · 1.15 Impact Factor
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    ABSTRACT: The absorption of lithium in montmorillonite [LiSi8(Al3Mg)O20(OH)4] was investigated using Density Functional Theory (DFT). The final position of lithium after absorption was found to be in good agreement with an experimental observation where lithium atom migrated from the interlayer into the vacant octahedral site of montmorillonite. The lithium absorbed on montmorillonite was held together by a very strong attraction between ions and exhibited an insulating behavior as depicted from the density of states curve. Due to the presence of lithium in the octahedral site of montmorillonite, the OH group reoriented itself perpendicular to the ab plane and an electron of lithium was transferred in order to compensate the existing net charge of montmorillonite caused by isomorphous substitutions. Relative small charge transfer was observed between lithium and montmorillonite.
    Journal of Nanoscience and Nanotechnology 04/2011; 11(4):2793-801. · 1.15 Impact Factor
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    ABSTRACT: Bimetallic systems such as Pt-based alloys or non-alloys have exhibited interesting catalytic properties but pose a major challenge of not knowing a priori how the electronic and chemical properties will be modified relative to the parent metals. In this work, we present the origin of the changes in the reactivity of Pt/Cr and Pt/Ni catalysts, which have been of wide interest in fuel cell research. Using spin-polarized density functional theory calculations, we have shown that the modification of Pt surface reactivity in Pt/Ni is purely of geometric origin (strain). We have also found that the Pt-Ni bonding is very weak, which explains the observed instability of Pt-Ni catalysts under electrochemical measurements. On the other hand, Pt/Cr systems are governed by strong ligand effect (metal-metal interaction), which explains the experimentally observed reactivity dependence on the relative composition of the alloying components. The general characteristics of the potential energy curves for O2 dissociative adsorption on the bimetallic systems and the pure Pt clarify why the d-band center still works for Pt/Cr despite the strong Pt-Cr bonding and high spin polarization of Pt d-states. On the basis of the above clarifications, viable Pt-Cr and Pt-Ni structures, which involve nano-sized alloys and non-alloy bulk catalyst, which may strike higher than the currently observed oxidation reduction reaction activity are proposed.
    Journal of Nanoscience and Nanotechnology 04/2011; 11(4):2944-51. · 1.15 Impact Factor
  • Yuji Kunisada, Hiroshi Nakanishi, Hideaki Kasai
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    ABSTRACT: We have investigated the O2 molecular and dissociative adsorption on Ag(111) surfaces. To clarify the adsorption properties, we performed first principles calculation based on spin-polarized density functional theory (DFT) with the generalized gradient approximation for the exchange--correlation energy. We calculated the potential energy surfaces (PES) for thirteen trajectories of O2, which gives us information with respect to the relevant six dimensional PES. From these results, we found that the effective energy barrier of O2 dissociative adsorption is about 1.24 eV. We also found that upon O2 molecular and dissociative adsorption, the magnetic moments per O atom were 0.52 muB and 0.32 muB, respectively. For reference, the isolated O2 and Ag(111) surfaces have the magnetic moments of 2.0 muB and 0.0 muB. In O2 dissociative adsorption, ferromagnetic behaviors were induced by ferromagnetic direct exchange interactions and superexchange interactions. Superlattice structures of O atoms which have an effective ferromagnetic superexchange interaction made ferromagnetic states feasible.
    Journal of the Physical Society of Japan 01/2011; 80. · 2.09 Impact Factor
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    ABSTRACT: Recently, the role of resistance random access memory (RRAM) is becoming extremely important in the development of nonvolatile memories. RRAM works by changing the resistance of the transition metal oxide contained in RRAM after the application of a sufficiently high voltage, however, this switching mechanism has not been fully clarified. In this study, by performing first principles calculations based on the density functional theory, we first investigate the change in the property of bulk CoO resulting from oxygen vacancies and charge carrier trapping in the vicinity of the oxygen vacancies. Next, we perform calculations for slab models of CoO in contact with Ta, W, and Pt electrodes and hence investigate the effects of oxygen vacancies at the interface between the CoO layer and the electrode layer. On the basis of the obtained results, we conclude that W is the most suitable electrode material compared with Ta and Pt.
    Japanese Journal of Applied Physics 01/2011; 50. · 1.07 Impact Factor

Publication Stats

381 Citations
203.50 Total Impact Points

Institutions

  • 1991–2014
    • Osaka University
      • • Division of Precision Science and Technology and Applied Physics
      • • Department of Applied Physics
      • • Department of Precision Science and Technology and Applied Physics
      • • Division of Applied Physiology
      Suika, Ōsaka, Japan
  • 2006
    • De La Salle University
      • Department of Physics
      Manila, NCR, Philippines