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Hokkaido University Collection of Scholarly and Academic Papers (136.069 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 61 - 80 de 172

  1. A new spectroelectrochemical cell for in situ measurement of Pt and Au K-edge X-ray absorption fine structure

    Kaito, Takahiro; Mitsumoto, Hisashi; Sugawara, Seiho; Shinohara, Kazuhiko; Uehara, Hiromitsu; Ariga, Hiroko; Takakusagi, Satoru; Asakura, Kiyotaka
    A new spectroelectrochemical cell to investigate the structure of Pt/Au nanoclusters using Pt and Au K-edge X-ray absorption fine structure (XAFS) measurements under the electrochemical conditions is developed. K-edge XAFS measurements for Pt and Au require a sample as thick as 1-2 cm, which prevents homogeneous potential distribution. We can measure in situ Pt and Au K-edge XAFS spectra and determine reasonable electrochemical surface areas using our developed spectroelectrochemical cell. This work provides a new approach to analyze Pt/Au core-shell nanoclusters. The new cell is designed to be applied to both spectra with high absorption-edge energies such as the K-edge...

  2. Fluorescent poly(boron enaminoketonate)s : synthesis via the direct modification of polyisoxazoles obtained from the click polymerization of a homoditopic nitrile N-oxide and diynes

    Matsumura, Tohru; Koyama, Yasuhito; Uchida, Satoshi; Yonekawa, Morio; Yui, Tatsuto; Ishitani, Osamu; Takata, Toshikazu
    Fluorescent poly(boron enaminoketonate)s (PBEKs) were synthesized via the polycycloaddition of a homoditopic nitrile N-oxide to diynes followed by other polymer reactions. Click polycycloaddition of the nitrile N-oxide to various diynes effectively produced polyisoxazoles in high yields. The polyisoxazoles were transformed into the corresponding fluorescent PBEKs by forming the poly(beta-aminoenone) intermediates and reacting these intermediates with (C6F5)(2)BF center dot OEt2. The solution and solid-state optical properties of the PBEKs were evaluated by ultraviolet-visible (UV-vis) and fluorescence spectroscopy.

  3. Quantitative evaluation of ball-milling effects on the hydrolysis of cellulose catalysed by activated carbon

    Yabushita, Mizuho; Kobayashi, Hirokazu; Hara, Kenji; Fukuoka, Atsushi
    The synthesis of glucose from cellulose is a critical roadblock for establishing a new sustainable cycle of biorefinery to produce bio-based and environmentally-benign chemicals. We have previously demonstrated that the pre-treatment ball-milling of solid cellulose and a solid catalyst ( mix-milling) drastically improves the yield of glucose and oligosaccharides; however, the effect of this type of ball-milling has not been quantitatively evaluated. In this study, we performed several model reactions and found that the mix-milling method drastically enhanced the solid-solid reactions, such as the hydrolysis of insoluble cellulose to soluble oligomers on the solid catalyst, but not liquid-solid reactions. The...

  4. Selective hydrodeoxygenation of lignin-related 4-propylphenol into n-propylbenzene in water by Pt-Re/ZrO2 catalysts

    Ohta, Hidetoshi; Feng, Bo; Kobayashi, Hirokazu; Hara, Kenji; Fukuoka, Atsushi
    Bimetallic Pt-Re/ZrO2 catalysts were developed for the selective hydrodeoxygenation of 4-propylphenol as a lignin model to n-propylbenzene in water. The addition of Re to Pt/ZrO2 improved the catalyst stability and product selectivity. Reaction temperature greatly affected not only reaction efficiency but also product distribution. n-Propylbenzene was obtained in up to 73% yield with ca. 80% selectivity. After the reaction, the catalyst was deactivated possibly due to water-induced wrapping of Pt nanoparticles in ZrO2. The reaction may involve the hydrogenation of 4-propylphenol to 4-propylcyclohexanol, followed by the dehydration to give 4-propylcyclohexene and the subsequent dehydrogenation to n-propylbenzene.

  5. Aqueous-phase hydrodeoxygenation of 4-propylphenol as a lignin model to n-propylbenzene over Re-Ni/ZrO2 catalysts

    Feng, Bo; Kobayashi, Hirokazu; Ohta, Hidetoshi; Fukuoka, Atsushi
    Aqueous-phase hydrodeoxygenation of 4-propylphenol as a lignin model to n-propylbenzene was carried out over various Ni based catalysts. Among the catalysts tested, Re-Ni/ZrO2 showed the best catalytic performance. Addition of Re decreased the Ni particle size and greatly improved the catalytic activity. H-2 pressure, Re to Ni ratio and reaction temperature were tuned in the optimization of reaction conditions for favorable formation of n-propylbenzene. Under the conditions of 300 degrees C and 4 MPa H-2, the yield of n-propylbenzene reached 54% over Re-Ni/ZrO2 (Re/Ni ratio 0.33) catalyst. It is suggested that the formation of n-propylbenzene proceeds via the hydrogenation of...

  6. An Experimental Approach to Transition States of Surface Reactions; Energy Partitioning in Repulsive Desorption

    Matsushima, Tatsuo; Orita, Hideo; Kokalj, Anton
    In a chemical reaction, both material conversions and energy partitioning take place simultaneously. Then its mechanism must be characterized from the viewpoints on both sides. Energy partitioning in surface reactions can be examined on product desorption processes when these are repulsive. This principle is exemplified in CO(a)+O(a) → CO2(g) on Pd(110)(1×1), and its application is proposed for N2O(a) → N2(g)+O(a) on the same surface. Structural information of desorption sites and active intermediates, as well as transition states, can be delivered from desorption- and azimuth-angle dependences of physical quantities of desorbing hyper-thermal products; i.e., anisotropic distributions of their flux, and translational...

  7. K-edge X-ray absorption fine structure analysis of Pt/Au core-shell electrocatalyst : evidence for short Pt-Pt distance

    Kaito, Takahiro; Mitsumoto, Hisashi; Sugawara, Seiho; Shinohara, Kazuhiko; Uehara, Hiromitsu; Ariga, Hiroko; Takakusagi, Satoru; Hatakeyama, Yoshikiyo; Nishikawa, Keiko; Asakura, Kiyotaka
    A carbon-supported Pt-shell Au-core electrocatalyst (Pt/Au/C) was prepared by sequential deposition of Pt ions on the surface of Au nanoparticles supported on carbon. The area-specific activity of the oxygen reduction reaction (ORR) for the prepared Pt/Au/C in 0.1 M HClO4, aqueous solution was approximately 2 times higher than that for a commercial carbon-supported Pt electrocatalyst (Pt/C). The core-shell structure was confirmed using electrochemical methods and Pt and Au K-edge X-ray absorption fine structure (XAFS) analysis. XAFS analyses indicated that the Pt-Pt bond distance for the Pt/Au/C catalyst was shorter than that for Pt foil and the Pt/C catalyst. In addition,...

  8. Enhanced photocatalytic activity by particle morphology : preparation, characterization, and photocatalytic activities of octahedral anatase titania particles

    Wei, Zhishun; Kowalska, Ewa; Ohtani, Bunsho
    Titania samples containing octahedral anatase particles (OAPs) were prepared by the ultrasonication-hydrothermal process of partially proton-exchanged potassium titanate nanowires. It was found that increase in the ultrasonication time changed the product morphology, with other structural properties such as specific surface area, crystalline size, and crystallinity remaining almost constant. The results of photocatalytic activity tests for those samples suggested higher activity of a sample with higher OAP content, especially for reactions in the presence of oxygen.

  9. Production of sugar alcohols from real biomass by supported platinum catalyst

    Kobayashi, Hirokazu; Yamakoshi, Yukiyasu; Hosaka, Yuto; Yabushita, Mizuho; Fukuoka, Atsushi
    The influence of lignin and inorganic salts on the catalytic activity was studied in the hydrolytic hydrogenation of real biomass by a supported Pt catalyst. The direct conversion of raw silver grass by Pt/carbon catalyst under H-2 pressure produced small amounts of sorbitol (2.8 wt%), xylitol (7.3 wt%), and other sugar alcohols. It has been suggested that lignin reduces the reactivity of cellulose, as lignin exists together with cellulose in the biomass and both compounds are insoluble in water. Moreover, even weak bases drastically change the product distribution with more by-products such as EG and PG. Bases enhance the decomposition...

  10. Speed-up of ab initio hybrid Monte Carlo and ab Initio path integral hybrid Monte Carlo simulations by using an auxiliary potential energy surface

    Nakayama, Akira; Taketsugu, Tetsuya; Shiga, Motoyuki
    Efficiency of the ab initio hybrid Monte Carlo and ab initio path integral hybrid Monte Carlo methods is enhanced by employing an auxiliary potential energy surface that is used to update the system configuration via molecular dynamics scheme. As a simple illustration of this method, a dual-level approach is introduced where potential energy gradients are evaluated by computationally less expensive ab initio electronic structure methods.

  11. Photophysics of cytosine tautomers : new insights into the nonradiative decay mechanisms from MS-CASPT2 potential energy calculations and excited-state molecular dynamics simulations

    Nakayama, Akira; Harabuchi, Yu; Yamazaki, Shohei; Taketsugu, Tetsuya
    A comprehensive picture of the ultrafast nonradiative decay mechanisms of three cytosine tautomers (amino-keto, imino-keto, and amino-enol forms) is revealed by high-level ab initio potential energy calculations using the multistate (MS) CASPT2 method and also by on-the-fly excited-state molecular dynamics simulations employing the CASSCF method. To obtain a reliable potential energy profile along the deactivation pathways, the MS-CASPT2 method is employed even for the optimization of minimum energy structures in the excited state and conical intersection (CI) structures between the ground and excited states. In the imino (imino-keto) form, we locate a new CI structure involving the twisting of the...

  12. Efficient sampling for ab initio Monte Carlo simulation of molecular clusters using an interpolated potential energy surface

    Nakayama, Akira; Seki, Nanami; Taketsugu, Tetsuya
    An approach is developed to enhance sampling for ab initioMonte Carlo and ab initio path integral Monte Carlo calculations of molecular clusters by utilizing an approximate potential as a guide to move in the configuration space more efficiently. The interpolatedpotential energy obtained by the moving least-squares method is used as an approximate potential, and this scheme is applied to a water molecule and small protonated water clusters (H3O+,H5O2+). It is found that the statistical errors are reduced by almost a factor of 3 in most calculations, which translates into a reduction in the computational cost by an order of magnitude....

  13. Control of selectivity, activity and durability of simple supported nickel catalysts for hydrolytic hydrogenation of cellulose

    Kobayashi, Hirokazu; Hosaka, Yuto; Hara, Kenji; Feng, Bo; Hirosaki, Yoshihiko; Fukuoka, Atsushi
    Efficient conversion of cellulose to sorbitol and mannitol by base metal catalysts is a challenge in green and sustainable chemistry, but typical supported base metal catalysts have not given good yields of hexitols or possessed durability. In this study, it has been demonstrated that a simple carbon-supported Ni catalyst affords up to 67% yield of hexitols in the conversion of cellulose, and that the catalyst is durable in the reuse experiments 7 times. In addition, the catalyst can be separated by a magnet thanks to a high content of Ni. Physicochemical analysis has indicated that the use of carbon supports...

  14. Gigantic chiroptical enhancements in polyfluorene copolymers bearing bulky neomenthyl groups : importance of alternating sequences of chiral and achiral fluorene units

    Watanabe, Kento; Koyama, Yasuhito; Suzuki, Nozomu; Fujiki, Michiya; Nakano, Tamaki
    An alternating copolymer consisting of achiral and chiral units emits remarkably efficient CPL on photo-excitation. The main-chain twist bias is enhanced by thermal annealing by the factor of 10(4) in the ground state. An anisotropy factor of the polymer in the excited state is greater by approximately an order of magnitude compared with that in the ground sate.

  15. Photo-induced helix-helix transition of a polystyrene derivative

    Wang, Yue; Sakamoto, Takeshi; Koyama, Yasuhito; Takanashi, Yuma; Kumaki, Jiro; Cui, Jiaxi; Wan, Xinhua; Nakano, Tamaki
    Poly(2,5-bis[4-((S)-2-methylbutyloxy)phenyl]styrene) having a helical conformation underwent helix-helix transition upon photo-irradiation. Conformational transition can significantly alter polymer properties, and so far thermal stereomutation has been studied. However, as for photo-induced mutation, only helix-helix transition (irreversible CD-active to CD-silent helix transition) of a polyacrylate has been explored. Here, we present mutation of the polystyrene derivative. Chiroptical, viscometric, and vibrational spectroscopic analyses indicated the polymer mutated from an optically active helix to another optically inactive helix with a different shape.

  16. High density monolayer of diisocyanide on gold surface as a platform of supported Rh-catalyst for selective 1,4-hydrogenation of α,β-unsaturated carbonyl compounds

    Jagtap, Sachin; Kaji, Yoshinori; Fukuoka, Atsushi; Hara, Kenji
    A high density monolayer of diisocyanide on gold surface was utilized as a platform of supported Rh catalyst for selective 1,4-hydrogenation of α,β-unsaturated carbonyl compounds. The catalyst exhibited high turnover numbers in a range of 50 000 to 150 000 per Rh atom and showed steady catalyst performance over six recycle usages.

  17. Linear response theory for the density matrix renormalization group : efficient algorithms for strongly correlated excited states

    Nakatani, Naoki; Wouters, Sebastian; Van Neck, Dimitri; Chan, Garnet Kin-Lic
    Linear response theory for the density matrix renormalization group (DMRG-LRT) was first presented in terms of the DMRG renormalization projectors [J. J. Dorando, J. Hachmann, and G. K.-L. Chan, J. Chem. Phys. 130, 184111 (2009)]. Later, with an understanding of the manifold structure of the matrix product state (MPS) ansatz, which lies at the basis of the DMRG algorithm, a way was found to construct the linear response space for general choices of the MPS gauge in terms of the tangent space vectors [J. Haegeman, J. I. Cirac, T. J. Osborne, I. Pizorn, H. Verschelde, and F. Verstraete, Phys. Rev....

  18. Revisiting the fundamental physical chemistry in heterogeneous photocatalysis : its thermodynamics and kinetics

    Ohtani, Bunsho
    Although the history of photocatalysis research is not so long, many researchers have studied photocatalysis and a large number of papers on photocatalysis have been published. The objectives of this review paper are to revisit the fundamentals of photocatalysis, especially its thermodynamics and kinetics, which have not been reexamined in recent studies, to clarify the problems, if any, that prevent developments in the field of photocatalysis, and to present insights for future progress.

  19. Solvent effects on the ultrafast nonradiative deactivation mechanisms of thymine in aqueous solution : Excited-state QM/MM molecular dynamics simulations

    Nakayama, Akira; Arai, Gaku; Yamazaki, Shohei; Taketsugu, Tetsuya
    On-the-fly excited-state quantum mechanics/molecular mechanics molecular dynamics (QM/MM-MD) simulations of thymine in aqueous solution are performed to investigate the role of solvent water molecules on the nonradiative deactivation process. The complete active space second-order perturbation theory (CASPT2) method is employed for a thymine molecule as the QM part in order to provide a reliable description of the excited-state potential energies. It is found that, in addition to the previously reported deactivation pathway involving the twisting of the C-C double bond in the pyrimidine ring, another efficient deactivation pathway leading to conical intersections that accompanies the out-of-plane displacement of the carbonyl...

  20. Silver-modulated SiO2-supported copper catalysts for selective hydrogenation of dimethyl oxalate to ethylene glycol

    Huang, Ying; Ariga, Hiroko; Zheng, Xinlei; Duan, Xinping; Takakusagi, Satoru; Asakura, Kiyotaka; Yuan, Youzhu
    We present the application of a one-step urea-assisted gelation method to prepare a SiO2-supported bimetallic catalyst composed of copper (Cu) and silver (Ag). Results show the remarkably enhanced performance of the catalyst for selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). Coupled with a series of characterization and kinetic studies, the improved activity is attributed to the formation of Cu nanoparticles containing Ag nanoclusters on the SiO2 surface. The coherent interactions between the Cu and Ag species help create the active Cu+/Cu-0 species in a suitable proportion and prevent the transmigration of bimetallic nanoparticles during the hydrogenation process....

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