Yasuhiro Tanizawa

Publications (3)6.17 Total impact

• Article: Three-Dimensional Structure Analyses of Cu Species Dispersed on TiO2(110) Surfaces Studied by Polarization-Dependent Total-Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS)

  Yasuhiro Tanizawa, Takafumi Shido, Wang-Jae Chun, Kiyotaka Asakura, Masaharu Nomura, Yasuhiro Iwasawa
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  ABSTRACT: Three-dimensional analysis of structures for dispersed Cu species on a TiO2(110) surface has been performed by a polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) technique. The dispersed Cu species were prepared by a chemical reaction between Cu(DPM)2 and a TiO2(110) surface and reduced with H2. The Cu(DPM)2 dissociatively adsorbed on the 2-fold site of bridging oxygen atoms of the TiO2(110) surface to form a Cu(DPM)(O-)2 species. Subsequent reduction of the Cu species with H2 at 363 K produced Cu3 trimers that were bound to the bridging oxygen atoms with the trimer plane inclined at about 30° from the TiO2(110) normal. There were direct Cu−O bonds at the Cu3 trimer/TiO2(110) interface in addition to Cu−Cu bonds. Further reduction at 473 K produced three-dimensional prismatic small Cu6 clusters by vertical growth in the [110] direction of the Cu fcc lattice. Orientations of the Cu3 triangle and Cu6 prism clusters may be regulated by the interaction between the Cu atoms and the bridging oxygen atoms on the anisotropic TiO2(110) surface.
  10/2003;
• Source

  Available from: Yasuo Izumi

  Article: Structure of low concentrations of vanadium on TiO2 determined by XANES and ab initio calculations.

  Yasuo Izumi, Fumitaka Kiyotaki, Hideaki Yoshitake, Ken-ichi Aika, Tae Sugihara, Takashi Tatsumi, Yasuhiro Tanizawa, Takafumi Shido, Yasuhiro Iwasawa
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  ABSTRACT: 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.
  Chemical Communications 11/2002; · 6.17 Impact Factor
• Source

  Available from: Yasuo Izumi

  Article: 0.6–3.0 wt% of Vanadium on/in Titania Monitored by X-ray Absorption Fine Structure Combined with Fluorescence Spectrometry

  Yasuo Izumi, Fumitaka Kiyotaki, Hideaki Yoshitake, Ken-Ichi Aika, Tae Sugihara, Takashi Tatsumi, Yasuhiro Tanizawa, Takafumi Shido, Yasuhiro Iwasawa
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  ABSTRACT: Selective XAFS measurements of 0.6–3.0 wt% V sites on/in TiO 2 were enabled utilizing a fluorescence spectrometer. The V sites were V IV species in the case of high-surface-area V-TiO 2 in contrast to V V species in the case of conventional V/TiO 2 catalysts, V supported on HSA-TiO 2 , and V-TiO 2 prepared in the absence of dodecylamine (general sol-gel method). Vanadium catalysts are used for the reduction of nitric oxide with ammonia, 1 the oxidation of naphthalene/o-xylene to phthalic anhydride, and the oxidation of butane to maleic anhydride. 2 The optimal catalytic performance in these applications has been reported to correspond to concentrations of V of less than a monolayer, dispersed on TiO 2 . When the concentration of V corresponds to monolayer levels, major V species has been proposed to be a monomeric monooxo 3 or dioxo vanadate, 4 polyvanadates 3 such as decavanadate ([V 10 O 28 ] 6À), 5 or to an epitaxial V 2 O 5 (010) layer over TiO 2 6 by Raman, 51 V NMR, UV-visible, etc. XAFS directly determines the local structure of non-crystalline materials. However, exceptionally it is very difficult to measure XAFS data for low concentrations of V in the TiO 2 matrix. When 0.6 wt% of V (1.1 wt% V 2 O 5) is mixed with TiO 2 , the V K-edge jump is only 0.037 compared to a total absorption of 4 in transmission mode. The photon number ratio of V K 1 /Ti K 1 is only 0.012 in fluorescence mode. When a solid-state detector (SSD; ÁE % 100 eV) is used, the V K 1 (4952.2 eV) peak can be separated from the Ti K 1 (4510.8 eV) peak. However, the Ti K 1;3 (4931.8 eV) still overlaps the V K 1 . The ratio of V K 1 /Ti K 1;3 is 0.058. The selective detection of V K 1;3 (5427.3 eV) is difficult using the SSD because scattered X-rays overlap. Auger or secondary photoelectrons derived from V are selectively monitored using an electron energy analyzer. However, these experiments need ultra-high vacuum, and in-situ measurements are impossible. In this Letter, XAFS combined with fluorescence spectrometry 7;8 was applied to selectively monitor low concentrations of V on/in TiO 2 . TiO 2 (P25, 60 m 2 g À1) was impregnated with V triisopropoxide oxide (1) in isopropanol solution (V/TiO 2). A high surface area (HSA; 1200 m 2 g À1) V-TiO 2 was prepared from compound 1, Ti tetraisopropoxide (2), and dodecylamine. 9 An aqueous solution was kept at 333 K for six days, and filtered. The obtained powder was heated at 453 K for ten days, and then washed by p-toluenesulfonic acid/ethanol. HSA-TiO 2 prepared in a similar procedure was
  Chemistry Letters. 01/2002; 31(11):1154-1155.