Publications (11)6.87 Total impact
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Article: Characterization of the Local Structure of the Vanadium Silicalite (VS-2) Catalyst and Its Photocatalytic Reactivity for the Decomposition of NO into N2 and O2
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ABSTRACT: The vanadium silicalite (VS-2) catalyst was hydrothermally synthesized, and a molecular level characterization was carried out by means of in situ photoluminescence, XAFS, ESR, FT-IR, UV−vis, solid-state wide-line 51V NMR, and XRD in the presence or absence of reactant molecules. These spectroscopic investigations of the VS-2 catalyst clearly show that the vanadium oxide moieties are incorporated within the zeolite framework as tetrahedrally coordinated vanadium oxide species having a terminal vanadyl group (VO) with a bond distance of 1.64 Å and three VO bonds with a bond distance of 1.73 Å. VS-2 catalyst also exhibits a charge-transfer absorption band at around 270−340 nm and an intense phosphorescence spectrum as a radiative decay from the charge-transfer excited triplet state at around 450−550 nm with a vibrational fine structure at 77 K. UV irradiation of the catalyst in the presence of NO was found to lead to the efficient photocatalytic decomposition of NO into N2 and O2 at 295 K. Dynamic studies of the phosphorescence in the presence of NO clearly indicate that the charge-transfer excited triplet state of the terahedrally coordinated vanadium oxide species plays a vital role in the photocatalytic decomposition of NO into N2 and O2. The results obtained by these spectroscopic measurements and photocatalytic reactions provide important information on the local structure of the vanadium oxide moieties incorporated within the zeolite framework and on the photocatalytic reactivity of the charge-transfer excited triplet state of the vanadium oxide species at the molecular level.07/1999; -
Article: Characterization of Vanadium Oxide/ZSM-5 Zeolite Catalysts Prepared by the Solid-State Reaction and Their Photocatalytic Reactivity: In Situ Photoluminescence, XAFS, ESR, FT-IR, and UV−vis Investigations
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ABSTRACT: The solid-state reaction of the ZSM-5 zeolite with V2O5 has been investigated by means of photoluminescence spectroscopy in combination with other spectroscopic techniques such as XAFS (XANES and FT-EXAFS), UV−vis, ESR, and FT-IR. It has been found that this reaction leads to the formation of the VO2+ species as well as the vanadium oxide species, (Si−O)3VO, which has a C3v symmetrical geometry and is located at two different sites, i.e., at positions accessible to small molecules as well as at inaccessible positions. These vanadium oxide species formed in the zeolite exhibits unique and specific photocatalytic reactivity toward the isomerization of cis-2-butene at 273 K.06/1998; -
Article: Design of photocatalysts encapsulated within the zeolite framework and cavities for the decomposition of NO into N2 and O2 at normal temperature
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ABSTRACT: The design of photocatalysts encapsulated within the zeolite frameworks and cavities is the most promising approach in developing photocatalysts which will operate efficiently and effectively towards the purification of toxic agents such as NOx and SOx in the atmosphere. In the present study, the vanadium silicalite (VS-2) and Ag+/ZSM-5 catalysts were prepared by hydrothermal synthesis and ion-exchange, respectively, and the in situ characterization of these catalysts and their photocatalytic reactivities for the decomposition of NO have been investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), ESR, FT—IR, LTV—VIS, solid-state NMR and XRD techniques along with an analysis of the reaction products. Results obtained with the VS-2 catalyst showed that vanadium oxide moieties are present within the zeolite framework as a 4-fold tetrahedrally coordinated vanadium oxide species having a terminal oxovanadium group (VO). UV irradiation of the VS-2 catalyst in the presence of NO led to the photocatalytic decomposition of NO to form N2, N2O and O2. On the other hand, it was found that the zeolite cavities can stabilize the Ag+ ions in an isolated state through their connection with two lattice oxygen anions of the zeolite (2-coordination geometry). These isolated Ag+ ions exhibit high photocatalytic reactivities for NO decomposition to form N2, N2O and NO2. Dynamic studies of the excited state of these catalysts showed that the charge transfer from the excited state of the vanadium oxide species or Ag+ ions to NO plays a vital role in the initiation of the decomposition of NO into N and O. These findings have demonstrated that metal oxide species and metal ions included within the zeolite frameworks and cavities are strong candidates for new types of environmentally applicable photocatalysts.Catalysis Today. -
Article: Photocatalytic decomposition of NO at 275 K on titanium oxide catalysts anchored within zeolite cavities and framework
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ABSTRACT: Titanium oxide species prepared in the Y-zeolite cavities via an ion-exchange method and those of the Ti-silicalite catalyst prepared hydrothermally exhibit high photocatalytic reactivity for the direct decomposition of NO into N2, O2 and N2O at 275 K with a high selectivity for the formation of N2. The in situ photoluminescence and XAFS investigations indicate that these titanium oxide species are highly dispersed and exist in a tetrahedral coordination in the zeolite cavities and its framework. The charge transfer excited state of these titanium oxide species plays a significant role in the direct decomposition of NO with a high selectivity for the formation of N2, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species and the bulk powdered TiO2 catalyst mainly produce N2O.Applied Surface Science. -
Article: Surface analyses of an alkali-treated Zr0.9Ti0.1Ni1.1Co0.1Mn0.6V0.2 alloy for use in nickel–metal hydride batteries
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ABSTRACT: An alkali-treated Zr0.9Ti0.1Ni1.1Co0.1Mn0.6V0.2 alloy was investigated with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) in combination with an Ar+ sputter-etching technology. As a result, it was found that alkali-treatment brought about a Ni-rich surface due to the selective dissolution of Ti, Co, Mn, V, etc. Such a Ni-rich surface plays a significant role in facilitating the activation of the alloy in charge–discharge cycle tests.Journal of Alloys and Compounds 280:99-103. · 2.29 Impact Factor -
Article: Electrochemical characteristics of an amorphous Mg0.9V0.1Ni alloy prepared by mechanical alloying
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ABSTRACT: Electrochemical characteristics of an amorphous MgNi alloy with Mg partially substituted by V were investigated. A Mg0.9V0.1Ni alloy prepared by mechanical alloying (MA) exhibited much better cycle life than MgNi alloy. It was found that the partial substitution of Mg in MgNi with V could suppress the formation of Mg(OH)2 on the alloy surface during the charge–discharge cycling in alkaline solution. This may have unveiled an important factor to improve cycle life of the Mg-based alloy for use in nickel–hydrogen batteries.Journal of Alloys and Compounds 280:104-106. · 2.29 Impact Factor -
Article: Hydriding and dehydriding characteristics of an amorphous Mg2Ni–Ni composite
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ABSTRACT: Hydriding and dehydriding characteristics of a Mg2Ni–Ni composite prepared by ball-milling Mg2Ni alloy with 70 wt. % Ni (Mg2Ni/Ni=1/1.28 in mole ratio) were investigated. As a result, it was found that the Mg2Ni–Ni composite showed a marked increase in the hydriding rate and the dehydriding commenced at much lowered temperature or even at room temperature, compared with Mg2Ni and ball-milled Mg2Ni alloys. Such a marked improvement in the hydriding and dehydriding characteristics, as well as the charge–discharge characteristics, by ball-milling the Mg2Ni alloy with Ni is probably due to the appearance of the homogeneous amorphous structure over the whole alloy particles.Journal of Alloys and Compounds 285:246-249. · 2.29 Impact Factor -
Article: Photoinduced surface chemistry
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ABSTRACT: A comprehensive understanding of the basic mechanisms and dynamics behind photoinduced surface chemistry is indispensable for the advancement of photo or photon-based sciences and technologies. Recent investigations into the mechanisms and dynamics of molecules adsorbed on photostimulated metal surfaces and the characterization of electronically excited molecules included within restricted molecular environments such as zeolite cavities have provided many useful applications for the control of photochemical surface reactions. Significantly and in practical terms, environmental applications of photocatalysis to design systems which will reduce toxic agents in the atmosphere and in water as well as operate effectively and efficiently under visible light will have profound implications for the future of this planet.Current Opinion in Solid State and Materials Science. -
Article: Surface analysis of an amorphous MgNi alloy prepared by mechanical alloying for use in nickel–metal hydride batteries
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ABSTRACT: An amorphous MgNi alloy prepared by mechanical alloying has been investigated by means of X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) in combination with an Ar+ sputtering technology. At the top surface (ca. 30 Å), Mg was dominant and existed in oxide forms while Ni mainly existed in the metallic state. Underneath the top surface, there was a layer enriched with metallic Ni which penetrates to more than 150 Å. Such a distribution of Mg and Ni at the surface layer tightly correlates to the unique hydriding and dehydriding properties of the amorphous MgNi alloy.Journal of Alloys and Compounds. -
Article: Photoluminescence property and photocatalytic reactivity of V-HMS mesoporous zeolites Effect of pore size of zeolites on photocatalytic reactivity
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ABSTRACT: The photoluminescence properties and photocatalytic reactivities of the V-HMS mesoporous zeolite have been investigated by means of in situ photoluminescence, UV-vis, EXAFS, XRD and ESR measurements. It was found that the V-HMS zeolite involves a vanadium species which is highly dispersed and incorporated in the framework of the mesoporous zeolites having a V=O bond and a C3v symmetry. This species plays an important role as the emitting site of this zeolite. It was also found that the zeolite exhibits photocatalytic reactivity under UV irradiation in the presence of cis-2-butene, resulting in the formation of trans-2-butene and 1-butene. The photocatalytic reactivity of the V-HMS mesoporous zeolite was found to be much higher than that of the V-silicalite microporous zeolite (VS-1). The efficiency of the dynamic quenching of the photoluminescence of the V-oxide species in the excited state in the V-HMS mesoporous zeolite by smaller molecules such as O2 was found to be the same as that of the VS-1 microporous zeolite. By comparing these results with results obtained on the VS-1 microporous zeolite photocatalyst, we can conclude that the pore size effect plays a significant role as one of the major factors which determine the photocatalytic reactivities of porous zeolite photocatalysts.Microporous and Mesoporous Materials. -
Article: Electrochemical characteristics of a homogeneous amorphous alloy prepared by ball-milling Mg2Ni with Ni
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ABSTRACT: Ball-milling Mg2Ni with metallic Ni (70 wt.% vs. Mg2Ni) lead to the formation of a homogeneous amorphous alloy, which exhibited a maximum discharge capacity of ca. 870 mAh g (Mg2Ni)−1 at 30°C. Its electrochemical and microstructural characteristics indicated that the homogeneous amorphous structure of the alloy was an important factor for such an improvement in charge–discharge characteristics.Journal of Alloys and Compounds.
