Shinji Tomura

Characterization of MCM-41 mesoporous molecular sieves containing copper and zinc and their catalytic performance in the selective oxidation of alcohols to aldehydes

MCM-41 mesoporous molecular sieves containing copper and zinc with different metal contents were synthesized at room temperature (RT) by the method of direct insertion of metal ions as precursors in the initial stage of synthesis. The physicochemical properties of the materials were thoroughly investigated employing X-ray powder diffraction, high-resolution transmission electron microscopy. UV-Visible diffuse reflectance spectroscopy, electron paramagnetic resonance spectroscopy, temperature programmed reduction and N adsorption-desorption methods, The results indicated that MCM-41 materials with long range hexagonal ordering could be successfully synthesized at RT in the presence of copper and zinc salts with the (Cu + Zn) contents of around 2-3 wt.%. A further increase in the metal content deteriorated the ordering of the materials. Removal of the template upon calcination resulted in the formation of CuO-like species with a distorted octahedral coordination. The Cu2+ ions in the MCM-41 materials were reduced completely to metallic copper in the temperature range 230-260 degreesC. On the other hand, the presence of zinc together with copper impeded the Cu2+ reducibility. The catalytic partial oxidation of methanol and ethanol over CuMCM-41 and CuZnMCM-41 materials yielded corresponding aldehydes as predominant products. The activity for alcohol conversion increased with increasing copper content, and this indicated that the Cu2+ ions in the CuMCM-41 and CuZnMCM-41 materials were located on the readily accessible interior surfaces of the mesopores

Characterization of synthetic imogolite nanotubes as gas storage

Imogolite is a naturally occurring hydrated aluminumsilicate polymer that consists of a tubular structural unit having an external diameter of 2.3–2.7 nm and an inner diameter of ca. 1 nm. The tube length is from about 400 nm to several micrometers. The tube walls are composed of curved gibbsite-like sheets with SiOH groups on the inside and AlOH groups on the outside, having a composition (HO)3Al2O3SiOH [1]. Imogolite is common in the clay fraction of soils derived from glassy volcanic ashes or pumice beds, and it has also been found in many podzols [2, 3]. Several investigations concerning natural imogolite have been published [4–6]. A synthetic route for production of imogolite was described in 1977 from dilute solutions of aluminum chloride and monosilicic acid [7]. Crystallization takes place at a lower concentration of the starting solutions and low pH under the boiling point treatment [8]. However, the above common process does not produce a high yield of well-crystallized imogolite tubes. Recently, nanotubes composed of various materials such as carbon, boron nitride, and oxides have been investigated [9–11], in particular, carbon nanotubes, which have great potential as materials with novel properties that are not found in conventional graphite or carbon fullerene [12]. For instance, since the suggestion of highly efficient storage of a natural gas with single walled carbon nanotubes, experimental determinations of the storage capacity and the mechanism of the storage have been performed extensively [13]. In the present work, the authors attempt to improve a synthetic method and to characterize an aluminosilicate mineral forming such hollow tubular structures for the purpose of gas storage. Imogolite nanotubes were synthesized from a highly concentrated starting solution under hydrothermal conditions. In a typical synthetic procedure, 66.7 ml of Na4SiO4 solution (concn. 100 mmol/l) was mixed with the same amount of 150 mmol/l AlCl3 solution, and then 1 mol/l NaOH was added dropwise (1 ml/min) into the above homogeneous solution under stirring

Formation of a clay monolayer at an air–water interface

By measuring the surface pressure–area isotherm at an air-water interface, an ion-exchange adduct of synthetic saponite with trimethylstearylammonium cation has been revealed to form a monolayer which is transferred on a hydrophobic glass plate as an oriented multilayer film.

GROWTH CONDITIONS AND GENESIS OF SPHERICAL AND PLATY KAOLINITE

Spherical and platy kaolinite crystals were prepared under several hydrothermal conditions. Spherical kaolinite was produced mainly at high solid/water ratio (1/4) and at low temperatures (150°-200°C). Platy kaolinite predominated in products from experiments with intermediate solid/water ratios (1/256-1/16) and at high temperatures. Boehmite predominated at low solid/water ratios (1/4096) at all experimental temperatures (180°-220°C). The results indicate that the growth of the spherical kaolinite was favored at high degrees of supersaturation, whereas the growth of the platy kaolinite was favored at relatively low degrees of supersaturation.

Study on intelligent humidity control materials: Water vapor adsorption properties of mesostructured silica derived from amorphous fumed silica

The intelligent humidity control materials were synthesized using fumed silica and quaternary alkylammonium surfactant (decyl-, dodecyl-, tetradecyl- and hexadecyl-trimethylammonium chlorides) as a liquid-crystal template under hydrothermal conditions. X-ray diffraction and transmission electron micrographs indicate that a homogeneous hexagonal structure of SiO2 was formed for those products. The mesostructured products had high B.E.T. surface areas between 960 and 1300 m2/g, with uniform mesopore diameters of 2–4 nm. These physical quantities were controlled by varying the size of the organic template. Water vapor adsorption isotherms for these materials possess a sharp increase in adsorption when the relative water vapor pressure is at 40–60%. Over this range of pressures, the maximum amount of adsorbed water content is between 40 and 90%. These silicates have the potential to be effectively used as humidity control elements in construction materials.

Synthesis of new Sn incorporated layered double hydroxides and their evolution to mixed oxides

A new series of MgIIAlIIISnIV hydrotalcite (HT)-like layered double hydroxides (LDHs) with Mg:Al:Sn = 3:1:0 to 3:0:1 were synthesized for the first time by a simple coprecipitation method at room temperature. The physicochemical properties of both as-synthesized and their thermally decomposed products were investigated in detail by various analytical and spectroscopic methods such as powder X-ray diffraction (PXRD), chemical analysis, scanning electron microscopy (SEM), FT-IR spectroscopy, 119Sn and 27Al MAS NMR, simultaneous TG/DTA, and N2 adsorption−desorption experiments. A single phase corresponding to LDH could be obtained in the composition range Mg:Al:Sn = 3:1:0 to 3:0.7:0.3. Above this composition, in addition to LDH, the MgSn(OH)6 phase also was formed. The 119Sn NMR showed a broad signal in the range −525 to −660 ppm for Sn atoms existing in a distorted octahedral environment. Thermal calcination of MgAlSn-LDHs at 450 or 700 °C resulted in the formation of MgO-like solid solution, in which both ...

Structure refinement of synthetic deuterated kaolinite by rietveld analysis using time-of-flight neutron powder diffraction data

The crystal structure of synthetic deuterated kaolinite was refined by Rietveld analysis using time-of-flight (TOF) neutron powder diffraction data. For non-hydrogen atoms, Cl symmetry was assumed. Starting models were tested in which only the direction of O-D vectors was varied. The constraints were introduced to all Al-O, Si-O and O-D bonds. The refinement adopting the former gives Pl(C1), a = 5.169(1) Å, b = 8.960(2) Å, c = 7.410(2) Å, α = 91.26(2)°, ß = 104.99(2)°, γ = 89.93(1)°, Rwp = 3.17%, R1 = 5.78% and S = 1.34 with constraints of l(Al-O)= 1.93 ± 0.05 Å, l(Si-O)= 1.62 ± 0.03 Å and l(D-O) = 0.95 ± 0.15 Å. The inner O-D vector points toward the tetrahedral sheet. All inner-surface O-D groups form H bonding with basal O atoms in the next kaolinite layers. The results agreed with those obtained from natural kaolinite.

EFFECTS OF THE STRUCTURE OF SILICA-ALUMINA GEL ON THE HYDROTHERMAL SYNTHESIS OF KAOLINITE

Kaolinite was hydrothermally synthesized from two kinds of silica-alumina gels to examine the effect of the structure of the starting material. Two kinds of gels were prepared by precipitation at different pH conditions (pH = 9.6 and 4.2) from solutions containing water glass and aluminum sulfate. Na ions in the gels were removed with a resin before the hydrothermal treatment, but a slight amount of sulfate ions was still present in the gels. The nuclear magnetic resonance spectra of the starting gels suggested that the gel prepared at pH 9.6 consists of networks with alternating SiO4- and A1O4-tetrahedra (partially AlO6-octahedra), whereas the gel prepared at pH 4.2 consists of a sheet structure related to allophane. After the hydrothermal treatment at 220°C for 9 days, kaolinite particles with spherical shape were obtained from the former gel, and platy kaolinite was crystallized from the latter one. The difference in morphology of synthetic kaolinite was attributable to the structures of the starting gels, and the pH values in the hydrothermal reactions were not very significant to the morphology.

Effects of solution chemistry on the hydrothermal synthesis of kaolinite

The hydrothermal synthesis of kaolinite was examined in the Al2O3-SiO2-H2O system to study inhibitory effects of additional ions on the formation of kaolinite. Syntheses were carried out with amorphous starting materials and salt solutions of various concentrations in Teflon pressure vessels at 220°C for 5 days. The reaction products were characterized by XRD, IR, DTA-TG, NMR and TEM. In all of the runs using solutions with cation concentrations less than 0.001 M, no significant effect on the formation of kaolinite was observed. The inhibitory effect of the univalent cations Li+, Na+ or K+ was less than that of divalent cations such as Mg2+ or Ca2+. The addition of trivalent Fe3+ or excess Al3+ ions interfered with the formation of kaolinite significantly. Sulfate and acetate solutions interfered with the formation of kaolinite more than chlorides and nitrates. No crystalline product was obtained using a 1.0 M basic solution of carbonate or hydroxide. The addition of the lithium ion to the system affected the crystallization of kaolinite only slightly. The use of 0.1 M LiCl and LiNO3 solutions for the syntheses improved crystallization of kaolinite along the [001] direction.

Synthesis and characterization of CuO containing mesoporous silica spheres

A new series of mesoporous silica spheres containing nanodispersed copper oxides were synthesized in H2O/EtOH/ammonia solution at room temperature. The mesoporous structures were characterised using X-ray powder diffraction and N2 adsorption-desorption techniques. Scanning electron micrograph and transmission electron micrograph revealed that the MCM-41 particles have spherical morphologies. The DTA curve of pure MCM-41 exhibited a sharp single exothermic peak between 290°C and 340°C, while a broad peak with several shoulders in the temperature range between 180°C and 380°C was observed for Cu-MCM-41, indicating the possible complexation of Cu2+ with surfactants adhering to the inner surfaces of the mesopores. Electron paramagnetic resonance spectra of uncalcined samples revealed that Cu2+ ions are in an octahedral or distorted octahedral coordination with nitrogen ligands of the surfactant while in the calcined samples they are coordinated with oxygen of the MCM-41 framework. The redox properties of samples were examined by a temperature-programmed reduction and N2O passivation method. The results indicate that CuO with increasing particle size could be formed in the mesoporous materials with increasing Cu contents, and this decreased the reducibility of the resulting CuO.