Hisao Yoshida

Heterogeneous photocatalytic hydrogen production from water and biomass derivatives

Hydrogen, a clean energy carrier, should be produced from not the irreproducible fossil fuels but renewable resources. Currently hydrogen is mainly produced by the reforming of petroleum and natural gas at high temperature, which consumes huge energy. Thus, development of an alternative hydrogen production method is absolutely imperative to mitigate the environmental and energy issues. Photocatalytic hydrogen production from water and renewable resources is one of the attractive systems, since it can utilize the solar energy. In this short review, we remind you that the systems of the photocatalytic hydrogen production from water and biomass derivatives, such as ethanol, glycerol, sugars and methane, should be considered as available candidates for the hydrogen production method from renewable resources and solar energy, and these systems have been improved by developments of new photocatalysts with some cocatalysts, modifications of photocatalysts, optimization of reaction conditions, and so on.

Quinolone resistance mutations in the DNA gyrase gyrA and gyrB genes of Staphylococcus aureus.

A 6.4-kb DNA fragment containing the DNA gyrase gyrA and gyrB genes was cloned and sequenced from the quinolone-susceptible Staphylococcus aureus type strain ATCC 12600. An expression plasmid was constructed by inserting the cloned genes into the Escherichia coli-S. aureus shuttle vector pAT19, and deletion plasmids carrying only functional gyrA and gyrB genes were derived from this plasmid. An efficient transformation system for S. aureus RN4220 was established by using these plasmids. Quinolone-resistant mutants of S. aureus RN4220 were isolated by three-step selection with quinolones. The first- and second-step mutants were considered to be transport mutants, and the third-step mutants were divided into five groups with respect to their resistance patterns and transformation results with gyrA and gyrB genes. Sequencing analysis of the resulting mutant gyrase genes showed that they had the following point mutations: group 1, Ser-84 (TCA) to Leu (TTA) in GyrA; group 2, Ser-84 (TCA) to Ala (GCA), Ser-85 (TCT) to Pro (CCT), or Glu-88 (GAA) to Lys (AAA) in GyrA; group 3, Asp-437 (GAC) to Asn (AAC) in GyrB; group 4, Arg-458 (CGA) to Gln (CAA) in GyrB; and group 5, Ser-85 (TCT) to Pro (CCT) in GyrA and Asp-437 (GAC) to Asn (AAC) in GyrB. When the gyrA and/or gyrB mutants were transformed with the wild-type gyrA and/or gyrB plasmids, they became quinolone susceptible, but transformants with the plasmids having the same mutations on the gyrA and/or gyrB genes did not confer susceptibility. These results indicate that mutations in both gyrA and gyrB can be responsible for quinolone resistance in S. aureus.

Selective oxidation of liquid hydrocarbons over photoirradiated TiO2 pillared clays

Abstract Selective photo-oxidation of benzene and cyclohexane were investigated by using TiO2 pillared clays (mica, montmorillonite and saponite). The characterization results indicated that all the TiO2 pillared clays contain TiO2 with similar structure, anatase-like small particles, in the different silicate layers of clays. The solvent effect on the photo-oxidation of benzene on TiO2 pillared clay was significant; both the activity and selectivity were increased by an addition of 10% water in acetonitrile solvent and they were further increased when the reaction was performed in an aqueous environment. In the latter condition, TiO2 pillared clays showed higher selectivity to oxygenates than TiO2 (Degussa P25). The product distribution among oxygenates also depends on the type of the clay host, indicating that the photocatalytic properties of TiO2 depend strongly on the type of clay host. For the cyclohexane photo-oxidation, TiO2 pillared clay showed much higher selectivity than TiO2, possibly because of the hydrophobic nature of pillared clay.

Adsorptive and photocatalytic performance of TiO2 pillared montmorillonite in degradation of endocrine disruptors having different hydrophobicity

Abstract TiO 2 pillared clay was applied for the adsorption-photocatalytic degradation of the endocrine disruptors with various hydrophobicities (di- n -butyl phthalate, diethyl phthalate, dimethyl phthalate and bisphenol-A). The hydrothermal treatment developed the crystallinity of the TiO 2 pillar and the size of the TiO 2 crystallites, and enhanced the photocatalytic degradation rate. However, the hydrothermal treatment in hard condition made the specific photocatalytic activity decrease since the size of crystallites increased. The surface hydrophobicity of the pillared clay was not affected so much, but reduced slightly, by the hydrothermal treatment. Higher hydrophobic endocrine disruptor was more adsorbed and enriched on the TiO 2 pillared clay. Enrichment of the reactant enhanced the rate of photocatalytic degradation on the pillared clay.

XPS, XANES and EXAFS investigations of CuO/ZnO/Al2O3/ZrO2 mixed oxide catalysts

Systematic X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (AES), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were undertaken to investigate the electronic structure, chemical states and local geometry of the active species in the CuO/ZnO/Al2O3/ZrO2 multicomponent mixed oxide catalysts employed in the oxidative steam reforming of methanol (OSRM) reaction for H2 production. The core level XPS and AES indicated the existence of CuO and ZnO-like species. Two kinds of zirconium species, one similar to that of ZrO2 and another with relatively higher electron density were noticed from the Zr 3d core level XPS of Zr- containing catalysts. The valence band (VB) XPS studies revealed that for Zr-containing catalysts, the Cu 3d anti-bonding orbital splits from the main VB and shifts toward lower binding energy (BE). The surface Cu/(Al + Zr) ratios were found to be close to those in the bulk while segregation of Zn at the surface was evidenced in all samples. The XANES and EXAFS results also indicated the existence of CuO and ZnO-like species, whose local environments are modified with respect to the chemical composition. The EXAFS study of the Zr-containing catalysts indicated the existence of a “Cu–O–Zr” bonding with a Cu–Zr distance in the range 3.5 to 3.9 A. The results indicated the existence of a Cu–Zr synergistic interaction in these catalysts which improved the catalytic performance in the OSRM reaction

Mechanism of action of quinolones against Escherichia coli DNA gyrase.

The mechanism of action of quinolones was investigated by use of various DNA gyrases reconstituted from wild-type and mutant GyrA and GyrB proteins of Escherichia coli. The quinolone sensitivities of the DNA supercoiling activity of the gyrases were generally parallel to the quinolone susceptibilities of strains having the corresponding enzymes and depended on gyrase subunits but not on substrate DNA. [3H]Enoxacin did not bind to gyrase alone or DNA alone but bound to gyrase-DNA complexes when measured by a gel filtration method. There appeared to be two enoxacin binding phases, at low and high enoxacin concentrations, for the wild-type gyrase-DNA and type 2 GyrB (Lys-447 to Glu) mutant gyrase-DNA complexes but only one enoxacin binding phase at the concentrations used for the GyrA (Ser-83 to Leu) mutant gyrase-DNA and type 1 GyrB (Asp-426 to Asn) mutant gyrase-DNA complexes. New enoxacin binding sites appeared in the presence of enoxacin, and the enoxacin binding affinities for the sites, especially at low enoxacin concentrations, near the MICs for the strains having the corresponding gyrases, correlated well with the enoxacin sensitivities of the gyrases and the MICs. From the results obtained, we propose a quinolone pocket model as the mechanism of action of quinolones, in which quinolones exert their action through binding to a gyrase-DNA complex and the quinolone binding affinities for the complex are determined by both GyrA and GyrB subunits in concert. Images

The support effect on propane combustion over platinum catalyst: control of the oxidation-resistance of platinum by the acid strength of support materials

Abstract The support effect on the low temperature propane combustion over supported platinum catalyst was studied by using a series of metal oxides as support materials: MgO, La 2 O 3 , ZrO 2 , Al 2 O 3 , SiO 2 , SiO 2 –Al 2 O 3 , and SO 4 2− –ZrO 2 . The catalytic activity varied with the support materials, and the platinum supported on more acidic support material showed higher activity. The support effect on the oxidation state of platinum was investigated by Pt L II - and L III -edge XANES. In the oxidizing atmosphere, platinum on the acidic support materials was less oxidized than that on the basic one, indicating that the oxidation-resistance of platinum is enhanced with the increase in the acid strength of support materials. This support effect in the oxidizing atmosphere is entirely different from that in the reducing atmosphere; the electron-deficiency of platinum increases with the increase in the acid strength of support materials under the reducing atmosphere. The relation between the catalytic activity and the oxidation state of platinum clearly indicates that the variation of the catalytic activity with the support materials come from the variation of the oxidation state of platinum, and that support materials affect the catalytic activity through the control of the oxidation state of platinum. These results suggest that the acid strength of support materials is an important factor for the design of the active supported platinum catalyst for the reaction under the oxidizing atmosphere.

Photocatalytic conversion of methane

Various efforts have been carried out to convert methane to more useful chemicals and hydrogen. However, due to its high stability, high energy is usually consumed for its conversion, which still remains as a problem to be solved. Recently, photocatalysis has been proposed to be one of the answers to break the thermodynamic barrier. This tutorial review provides a brief history about developments in the methane conversion and specially highlights the developments in the photocatalytic conversion of methane, such as methane coupling and methane conversion with other molecules.

Preparation of highly dispersed niobium oxide on silica by equilibrium adsorption method

Abstract Two series of Nb 2 O 5 /SiO 2 catalysts are prepared by an equilibrium adsorption method (type A) and a conventional evaporation to dryness method (type E). The loading amounts of type A catalysts were low ( ~ 0.2 wt% as Nb 2 O 5 ) and those of type E catalysts were varied from 0.1 to 10 wt%. UV/VIS diffuse reflectance spectra of the catalyst samples show that micro particles of Nb 2 O 5 ) are present on the catalysts with high-loading and monomeric or oligomeric niobate species are present on the catalysts with low-loading. By analyzing luminescence spectra of the low-loading samples, we conclude that the type A catalyst contains monomeric NbO 4 tetrahedra and the type E catalyst oligomeric NbO 4 tetrahedra. Propene photo-oxidation on type A catalysts yields propene oxide selectively, formed on monomeric NbO 4 , whereas the photo-oxidation on the type E catalyst with low-loading yields propanal selectively. Propanal is the product in decomposition of propene oxide on oligomeric NbO 4 tetrahedra.

The support effect on platinum catalyst under oxidizing atmosphere: improvement in the oxidation-resistance of platinum by the electrophilic property of support materials

Abstract The support effect on platinum catalyst for low temperature propane combustion was investigated by using a series of platinum catalysts with different acid strengths support materials and different platinum dispersions. The catalytic activity of platinum catalyst varied with both the acid strength of support materials and the platinum dispersion. On each support material, the turnover frequency increased with the decrease in platinum dispersion. This variation in the turnover frequency is attributed to the variation in the oxidation state of platinum, since it was clarified by Pt L II and L III -edge XAFS that platinum with small dispersion is less oxidized than that with large dispersion. The turnover frequency also varied with the acid strength of support materials; the turnover frequency increased with the increase in the acid strength of support materials at the same dispersion. The Pt L II and L III -edge XAFS investigation clearly indicated that platinum on the acidic support material is less oxidized than that on basic material. Thus, it is clearly shown that the support materials affect the catalytic activity of platinum through the control of the oxidation-resistance of platinum by its electrophilic/electrophobic property, demonstrating that the electrophilic/electrophobic property of support materials is an important factor for the design of platinum catalyst under the oxidizing atmosphere.