Masahiro Sadakane

Preparation of 3-D ordered macroporous tungsten oxides and nano-crystalline particulate tungsten oxides using a colloidal crystal template method, and their structural characterization and application as photocatalysts under visible light irradiation

Three-dimensionally ordered macroporous (3DOM) tungsten(VI) oxide (WO3) was prepared using a colloidal crystal template method. Well-ordered 3DOM WO3 was prepared with a high pore fraction using ammonium metatungstate ((NH4)6H2W12O40), a Keggin-type dodecatungstate, as a tungsten precursor; WO3 materials prepared by other commercially available W precursors, tungsten chloride (WCl6), tungsten(V) ethoxide (W(OEt)5), and phosphotungstic acid (H3PW12O40), have a low 3DOM pore fraction. These WO3 materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) analysis of nitrogen adsorption isotherm, and Raman spectroscopy. Non-porous WO3 prepared from ammonium metatungstate without a poly(methyl metacrylate) (PMMA) template grew to crystal sizes of up to several micrometres with a low specific surface area (ca. 1–2 m2 g−1). In the presence of a colloidal crystal template of PMMA spheres, WO3 crystal grew in the nanometre-sized voids between the PMMA spheres, and the specific surface area thus increased up to ca. 30 times compared to non-porous WO3. The surface area is tunable by changing the PMMA sphere diameter. Calcination of the 3DOM WO3 produced WO3 nano-crystalline particles by sintering-induced disassembly. After Pt-loading, these WO3 materials showed higher photocatalytic activity compared to non-porous WO3 for decomposition of acetic acid in air under visible light irradiation.

Molybdenum–Vanadium‐Based Molecular Sieves with Microchannels of Seven‐Membered Rings of Corner‐Sharing Metal Oxide Octahedra

Crystalline microporous oxides such as zeolites are indispensable materials in various applications ranging from industrial processes to everyday life, such as catalysts, ion-exchange materials, and molecular sieves. Most of them contain tetrahedrally coordinated metal atoms, but octahedrally coordinated metal centers have recently attracted much attention as building blocks of crystalline microporous metal oxides. Manganese oxides (pyrolusite, hollandite, todorokite, and romanechite) with micropores are the only crystalline porous materials based solely on octahedra (octahedral molecular sieves). These manganese oxides contain microtunnel pores consisting of {MnO6} octahedra that share edges and corners. Here we describe a novel type of octahedral molecular sieve, namely, crystalline orthorhombic Mo3VOx (x = 11.2), in which the microchannel is constructed by seven-membered rings of corner-sharing MO6 (M = Mo or V) octahedra. It is isostructural to orthorhombic MoVNbTeO compounds, which are very active and selective oxidation catalysts for light alkanes. These mixed metal oxides have a layered orthorhombic structure with a slab composed of sixand seven-membered rings of corner-sharing {MO6} octahedra and pentagonal {(M)M5O27} units with a {MO7} pentagonal bipyramid and five edge-sharing {MO6} octahedra, whereM is Mo, V, or Nb. The layered sixand seven-membered rings form channel structures. The Te atom is believed to be located both in the sixand seven-membered rings and block the channel. Recently, we succeeded in preparing an orthorhombic Mo3VOx compound that contains only Mo and V, [6] in which the channel is expected not to be blocked (Figure 1).

An orthorhombic Mo3VOx catalyst most active for oxidative dehydrogenation of ethane among related complex metal oxides

Four distinct structural types (orthorhombic, trigonal, tetragonal and amorphous) of Mo3VOx catalyst were each synthesized by a hydrothermal method as a single phase, characterized structurally and tested for oxidative dehydrogenation of ethane. A common structural feature of the catalysts is that the materials are a layer-type structure and constructed with pentagonal {Mo6O21} units. The arrangement of the pentagonal units can form heptagonal channels to create different structural features. The orthorhombic Mo3VOx catalyst has microporosity due to the open heptagonal channels adsorbing nitrogen molecules and showed the highest activity for the reaction among four distinct catalysts. Furthermore, this phase appeared to be most active, currently, compared to other complex metal oxide catalysts reported. An observed positive relation between the microporosity and the oxidation activity suggests that the catalytic oxidation takes place at the heptagonal channels.

Dimerization of mono-ruthenium substituted α-Keggin-type tungstosilicate [α-SiW11O39RuIII(H2O)]5− to µ-oxo-bridged dimer in aqueous solution: synthesis, structure, and redox studies

We report the dimerization of a mono-ruthenium(III) substituted α-Keggin-type tungstosilicate [α-SiW11O39RuIII(H2O)]5− to a µ-oxo-bridged dimer [{α-SiW11O39Rum}2O]n− (m = III, n = 12; m = IV/III, n = 11; m = IV, n = 10). Single crystal X-ray structure analysis of Rb10[{α-SiW11O39RuIV}2O]·9.5H2O (triclinic, P, with a = 12.7650(6) A, b = 18.9399(10) A, c = 20.2290(10) A, α = 72.876(3)°, β = 88.447(3)°, γ = 80.926(3)°, V = 4614.5(4) A3, Z = 2) reveals that two mono-ruthenium substituted tungstosilicate α-Keggin units are connected through µ-oxo-bridging Ru–O–Ru bonds. Solution 183W-NMR of [{SiW11O39RuIV}2O]10− resulted in six peaks (−63, −92, −110, −128, −132, and −143 ppm, intensities 2 : 2 : 1 : 2 : 2 : 2) confirming that the µ-oxo bridged dimer structure is maintained in aqueous solution. The dimerization mechanism is presumably initiated by deprotonation of the aqua-ruthenium complex [α-SiW11O39RuIII(H2O)]5− leading to a hydroxy-ruthenium complex [α-SiW11O39RuIII(OH)]6−. Dimerization of two hydroxy-ruthenium complexes produces the µ-oxo bridged dimer [{α-SiW11O39RuIII}2O]12− and a water molecule. The Ru(III) containing dimer is oxidized by molecular oxygen to produce a mixed valence species [{α-SiW11O39RuIV-III}2O]11−, and further oxidation results in the Ru(IV) containing [{α-SiW11O39RuIV}2O]10−.

Sunlight-induced efficient and selective photocatalytic benzene oxidation on TiO2-supported gold nanoparticles under CO2 atmosphere.

The sunlight-induced photocatalytic oxidation of aqueous benzene on TiO(2)-supported gold nanoparticles was considerably improved when the reaction was conducted under a CO(2) atmosphere. 13% yield and 89% selectivity of phenol was obtained on P25-supported gold nanoparticles under 230 kPa of CO(2).

Carbonyl-ruthenium substituted alpha-Keggin-tungstosilicate, [alpha-SiW(11)O(39)Ru(II)(CO)](6-): synthesis, structure, redox studies and reactivity.

The carbonyl-ruthenium substituted undecatungstosilicate [alpha-SiW(11)O(39)Ru(II)(CO)](6-) () was isolated as a caesium salt and successfully characterized by using (183)W and (13)C NMR, elemental analysis, IR, UV-vis and cyclic voltammetry (CV). Polyanion represents the first example of a metal-carbonyl moiety being fully incorporated into the polyoxometalate (POM). As a result, the Ru(CO) moiety became redox active and was reversibly oxidized to the one-electron ruthenium(iii) derivative, [alpha-SiW(11)O(39)Ru(III)(CO)](5-). This Ru(III)(CO) moiety was unexpectedly stable in aqueous solution compared to the organo-ruthenium carbonyl derivatives and could be detected by using UV-vis and in situ IR coupled with electrolysis. The oxidized ruthenium(iii) derivative slowly released CO in aqueous solution, resulting in the aqua species [alpha-SiW(11)O(39)Ru(III)(H(2)O)](5-) and then the dimeric POM species by condensation. Furthermore, could be converted to the corresponding aqua polyanion by photo-irradiation.

Atomic-level imaging of Mo-V-O complex oxide phase intergrowth, grain boundaries, and defects using HAADF-STEM

In this work, we structurally characterize defects, grain boundaries, and intergrowth phases observed in various Mo-V-O materials using aberration-corrected high-angle annular dark-field (HAADF) imaging within a scanning transmission electron microscope (STEM). Atomic-level imaging of these preparations clearly shows domains of the orthorhombic M1-type phase intergrown with the trigonal phase. Idealized models based on HAADF imaging indicate that atomic-scale registry at the domain boundaries can be seamless with several possible trigonal and M1-type unit cell orientation relationships. The alignment of two trigonal domains separated by an M1-type domain or vice versa can be predicted by identifying the number of rows/columns of parallel symmetry operators. Intergrowths of the M1 catalyst with the M2 phase or with the Mo5O14-type phase have not been observed. The resolution enhancements provided by aberration-correction have provided new insights to the understanding of phase equilibria of complex Mo-V-O materials. This study exemplifies the utility of STEM for the characterization of local structure at crystalline phase boundaries.

Investigation of the manganese-substituted α-Keggin-heteropolyanion K6SiW11O39Mn(H2O) by cyclic voltammetry and its application as oxidation catalyst

Abstract The behavior of a manganese substituted α-Keggin silicon tungstoheteropolyanion (K 6 SiW 11 O 39 Mn(II)(H 2 O)) under electrochemical oxidation conditions was investigated by means of cyclic voltammetry in phosphate buffer. Substitution of the water ligand by counter anions (L: H 2 PO − 4 or HPO 2− 4 ) leading to SiW 11 O 39 Mn(II)(L) was observed. Replacement of the counter anion by an aquo ligand was observed in cyclic voltammetry by continuous cycling. After oxidation of SiW 11 O 39 Mn(II)(L) to SiW 11 O 39 Mn(IV)(L), this counter anion L was in turn substituted by OH − . The thus formed complex SiW 11 O 39 Mn(IV)(OH) oxidizes different alcohols, the reactivity of which decreases as follows: 1-phenyl-ethanol, benzylalcohol > iso -propanol > ethanol.

Important property of polymer spheres for the preparation of three-dimensionally ordered macroporous (3DOM) metal oxides by the ethylene glycol method: the glass-transition temperature.

We demonstrate that the glass-transition temperature (T(g)) of a polymer sphere template is a crucial factor in the production of three-dimensionally ordered macroporous (3DOM) materials. Metal nitrate dissolved in ethylene glycol-methanol was infiltrated into the void of a face-centered, close-packed colloidal crystal of poly(methyl methacrylate) (PMMA)-based spheres. The metal nitrate reacts with EG to form a metal oxalate (or metal glycoxylate) solid (nitrate oxidation) in the void of the template when the metal nitrate-EG-PMMA composite is heated. Further heating converts metal oxalate to metal oxide and removes PMMA to form 3DOM materials. We investigated the effect of T(g) of PMMA templates and obtained clear evidence that the solidification temperature of the metal precursor solution (i.e., nitration oxidation temperature) should be lower than the T(g) of the polymer spheres to obtain a well-ordered 3DOM structure.

Tetrahedral Connection of ε-Keggin-type Polyoxometalates To Form an All-Inorganic Octahedral Molecular Sieve with an Intrinsic 3D Pore System

A new type of polyoxometalate-based porous material was successfully synthesized. The new material is the first fully inorganic Keggin-type polyoxometalate-based microporous material with intrinsically ordered open micropores and is the third member of the small family of octahedral molecular sieves (OMSs). Twelve MoO6 or VO6 octahedra surround a central VO4 tetrahedron to form ε-Keggin polyoxometalate building blocks (ε-VMo9.4V2.6O40) that are linked by Bi(III) ions to form crystalline Mo-V-Bi oxide with a diamondoid topology. The presence of a tetrahedral shape of the ε-Keggin polyoxometalate building block results in arrangement of microporosity in a tetrahedral fashion which is new in OMSs. Owing to its microporosity, this Mo-V-Bi oxide shows zeolitic-like properties such as ion-exchange and molecule adsorption.