Найдено 413
Ничего не найдено
Preparation of calcium titanate photocatalysts for hydrogen production
Shimura K., Miyanaga H., Yoshida H.
Various CaTiO3 samples having different particle sizes, shapes, crystal defects and impurity phases were prepared by three methods, i.e., co-precipitation, homogeneous precipitation and solid-state reaction methods. The CaTiO3 samples were loaded with Pt co-catalyst (0.1 wt%) and examined for both the photocatalytic water decomposition (WD) and the photocatalytic steam reforming of methane (PSRM). The highest activities for the WD and the PSRM were obtained over the samples prepared by the solid-state reaction method from rutile and anatase TiO2, respectively. The controlling factors in their activity were discussed.
Influence of the preparation methods for Pt/CeO2 and Au/CeO2 catalysts in CO oxidation
Shimada S., Takei T., Akita T., Takeda S., Haruta M.
The influence of the preparation methods (IP:impregnation, DP:deposition-precipitation, SG:solid grinding) for Pt/CeO2 and Au/CeO2 was studied on the size and shape of metal particles and the catalytic activity for CO oxidation. The fine structures of these catalysts were examined by HR-TEM and were correlated to their catalytic properties. The size of metal particles depended on the preparation methods and increased in the order of DP
Preparation of gallium oxide photocatalysts for reduction of carbon dioxide
Yoshida H., Maeda K.
A series of gallium oxide samples prepared by homogeneous precipitation method consisted of homogeneous granules of short rod-like morphology with similar size; 300-500 nm in diameter and 1–2 μm in length. Calcination at various temperatures provided two polymorphs with various specific surface areas and crystallites sizes. The gallium oxide samples of low specific surface area photocatalytically promoted reduction of carbon dioxide by methane and non-oxidative coupling of methane, while those of high specific surface area additionally promoted consecutive photocatalytic reduction of carbon dioxide by produced hydrogen to give carbon monoxide selectively.
Selective preparation of β-MoO3 and silicomolybdic acid(SMA) on MCM-41 from molybdic acid precursor and their partial oxidation performances
Huong T.M., Phuc N.H., Ohkita H., Mizushima T., Kakuta N.
SMA(Mo/MCM-41Imp) and β-MoO3(Mo/MCM-41 Evap) were successfully prepared on MCM-41 using the molybdic acid solution. The molybdic acid solution is the effective precursor to generate selectively either SMA or β-MoO3, and those species are anchored on MCM-41 through the formation of SMA. The Mo/MCM-41Imp catalyst showed a good catalytic performance for partial oxidation of methane to formaldehyde while the Mo/MCM-41 Evap is a promising catalyst for partial oxidation of methanol to formaldehyde.
Nitrogen doped TiO2 photocatalyst prepared by low energy N+ implantation technique
Yoshida T., Kuda E.
A nitrogen doped TiO2 as a visible-light response photocatalyst was prepared by low energy N+ implantation technique. N+ -implanted TiO2 samples promoted the photocatalytic activity for degradation of methylene blue under visible-light irradiation. N 1s XPS and N K-edge XANES spectra of the photocatalytically active sample indicated that N replaces the O sites near the surface, whereas in the inactive samples N-O species are formed. We also found that the nitrogen concentration of the sample implanted with small amount of N+ (1 × 1021 m -2) is a little higher than that with large amount of N+ (3 × 1021 m-2). In the low energy (5 keV) N+ implantation, the sputtering of the sample atoms would be one of the important processes for controlling both the concentration and chemical state of the doped nitrogen.
Preparation of silica-coated Pt-Ni alloy nanoparticles using microemulsions and formation of carbon nanofibers by ethylene decomposition
Nakagawa K., Takenaka S., Matsune H., Kishida M.
I2 as a probe for aromatic rings in phenylene-bridged periodic mesoporous organosilica
Camarota B., Onida B., Goto Y., Inagaki S., Garrone E.
Periodic Mesoporous Organosilicas (PMOs) represent a new class of organic-inorganic hybrid materials suitable for a broad range of applications. In the present contribution iodine vapours were adsorbed on phenylene-bridged PMOs with hexagonal 2D pore structure. The adsorption was followed by UV-visible spectroscopy, and information was obtained concerning the electron donor ability of the structural aromatic rings. Traces of I 3 − species were also detected. A comparison between phenylene-bridged PMOs with two different degrees of molecular order in the walls revealed that aromatic rings in the material with amorphous walls are more available to interaction with iodine.
Alkylation of naphthalene over mesoporous metal substituted SBA-1 catalysts
Brzozowski R., Vinu A.
Alkylation of naphthalene with propylene to diisopropylnaphthalenes (DIPN) over AlSBA-1, GaSBA-1 and FeSBA-1 mesoporous catalysts was investigated. The AlSBA-1 and GaSBA-1 catalysts were promising for this purpose due to their high activity and stability and low 2,6-DIPN selectivity. However, the initially active FeSBA-1 samples deactivated quickly.
Photocatalytic degradation on Ni loaded Ti-containing mesoporous silica prepared by a photo-assisted deposition (PAD) method
Mohamed R.M., Ibrahim F.M., Mori K., Yamashita H.
The Ni/Ti-containing mesoporous silica catalysts were prepared via two different routs. The first one, by the name of a photo-assisted deposited (PAD) method, in which the nano-sized Ni catalyst can be highly deposited on Ti-containing mesoporous silica (PAD-Ni/Ti-HMS). The second one, the Ni was loaded on Ti-HMS with incipient wetness impregnation method (imp-Ni/Ti-HMS). It has been found that the photocatalytic activity of the PAD-Ni/Ti-HMS is higher than that of the imp-Ni/Ti-HMS and Ti-HMS for the decomposition of 2-propanol with O2 under UV-light irradiation.
Synthesis of nano-sized Pt metal particle on Ti-containing mesoporous silica and efficient catalytic application for hydrogenation of nitrobenzene
Shironita S., Mori K., Yamashita H.
A novel method to prepare the nano-sized Pt metal catalysts is proposed. Mesoporous silica containing highly dispersed titanium oxide species (Ti-HMS) can act as a platform to generate highly dispersed Pt metal particles, as confirmed by Pt LIII-edge XAFS and CO adsorption. The Pt metal particle on the Ti-HMS was smaller than that of without one. The nano-sized Pt metal catalyst is useful as efficient catalyst for hydrogenation of nitrobenzene, and higher reaction rate could be attained with smaller size of Pt metal particles.
Assembling mode of alumina and zirconia particles inside the mesopores of SBA-15 under high loading
Cheralathan K.K., Hirata H., Ogura M.
Loading high amount (> 30 wt%) of alumina and zirconia inside the mesopores of SBA-15 was accomplished by a simple procedure, wet impregnation and followed that by calcination and also by a procedure invented by us viz. loading the precursors and internally hydrolyze them inside the pores by employing NH 3 /H 2 O vapour at elevated temperature and subsequent calcination (VIH method). Loading without NH 3 /H 2 O vapour treatment caused pore blocking. But loading via VIH method led to alumina coated SBA-15 with relatively minimal pore blocking and zirconia coated SBA-15 without any pore blocking. Characterization of the prepared materials indicated that alumina prefers to be present inside the pores as nanocrystals where as zirconia coats on the pore walls as layer showing that the assembling mode of alumina and zirconia inside the mesopores of SBA-15 are different.
Vapor phase synthesis of mesoporous silica thin films with a 3D pore structure
Maruo T., Nagata K., Nishiyama N., Egashira Y., Ueyama K., Muzzillo C.P., Tate M.P., Hillhouse H.W.
Ordered mesoporous silica thin films were prepared using non-ionic alkyl poly(oxyethylene) surfactants (Brij56: C18EO10) by a vapor phase method. First, a Brij56/H2SO4 composite was deposited on a silicon substrate by spin-coating. The Brij56 film was treated with a tetraethoxysilane (TEOS) and hydrochloric acid (HCl) vapors in a closed vessel. The TEOS and HCl vapors were infiltrated into the film, resulted in a formation of the silica network. Results of a grazing angle of incidence small angle X-ray scattering (GISAXS) show that the films have an ordered structure with an Fmmm symmetry. From an Field emission scanning electron microscope (FESEM) observations, the film has a 3D pore structure.
Effects of structure-directing agents on hydrothermal conversion of FAU type zeolite
Jon H., Sasaki H., Inoue T., Itakura M., Takahashi S., Oumi Y., Sano T.
The hydrothermal conversion of FAU type zeolite with various structure-directing agents was investigated. The highly crystalline and pure RUT and MTN type zeolites were obtained in the presence of tetramethylammonium hydroxide and benzyl-trimethylammonium hydroxide, respectively. As compared to amorphous silica/γ-Al2O3 source, the crystallization rate for the formation of RUT type zeolite was clearly faster when FAU type zeolite was employed as Si and Al sources.
Preparation of AlMepO materials on steam-assisted conversion method
Maeda K., Imaizumi H., Sasaki Y., Yamazaki T., Suzuki T., Kiyozumi Y.
Microporous aluminomethylphosphonate AlMepO-β was prepared at 100–160°C in steam-assisted conversion (SAC) method from dry gel precursors. The sizes of the obtained crystals were considerably smaller compared with those prepared in hydrothermal method. By applying the SAC method to film preparation, a 40 μm-thick film-like polycrystalline layer of AlMepO-α was obtained on a porous alumina substrate. The layer was composed of many separate domains of ca. 200 nm in size, which are needle-like crystals.
A new synthesis route to nano-sized β-zeolite with organic silane containing surfactant
Venkatesan C., Aoyama K., Komura K., Sugi Y.
β-Zeolite (BEA) was hydrothermally synthesized in the presence of small amount of a cationic surfactant, [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride (ODSCl) along with a molecular template, tetraethylammonium hydroxide (TEAOH) by using different amount of Al in the starting gel. BEA100 with input SiO2/Al2O3 molar ratio of 100 exhibited 100 nm uniform sized spherical morphology and all Al are tetrahedrally incorporated in the framework and showed active for the isopropylation of m-cresol to thymol.
Vapour phase functionalization without degradation of the framework structure of periodic ordered mesoporous ethylenesilica
Nojima K., Yoshitake H.
We propose a new method for the functionalization of periodic ordered mesoporous ethylenesilica (MES) with amine functions but without significant damage to the framework structure. Brominated MES was successfully functionalized in the vapour of diethylenetriamine (DETA) and toluene, which provided a periodic mesoporous structure very similar to the original MES. In contrast, the liquid phase functionalization with DETA in toluene resulted in a disappearance of XRD peaks.
Synthesis of ordered mesoporous carbons in film morphology using organic-organic interaction approach
Tanaka S., Katayama Y., Nakatani N., Tate M.P., Hillhouse H.W., Miyake Y.
Preparation of ordered mesoporous carbon films without the use of an intermediate inorganic silica template was achieved from organic-organic assembly of thermally-decomposable triblock copolymer and thermosetting phenolic resin precursors. The films were formed by spin-coating followed by an evaporation-induced self-assembly. Afterwards, decompositon of the organic template and solidification of the carbon precursors are simultaneously performed through a direct carbonization process. Adjusted condition in the ratio of phenolic resin precursors and triblock copolymer allows one to tailor the final mesostructure which include 2D hexagonal phase (c2mm) and 3D face-centered orthorhombic symmetry (Fmmm). These film periodicity uniaxially-contracted normal to the film surface.
Mesoporous aluminosilicates assembled from dissolved LTA precursor
Tanaka S., Okada H., Miyake Y.
Zeolite Na-A dissolved in a HCl solution was used as aluminum and silica precursors for the synthesis of mesoporous aluminosilicates via a template-assisted method with an organic base tetramethylammonium hydroxide (TMAOH). Increasing the amount of TMAOH in the synthetic solution resulted in an increase in the aluminum content of the products. On the other hand, mesostructural periodicity was deteriorated with higher content of aluminum substituted in the framework. The samples with low Si/Al ratios less than 5 have wormhole-like pore structure, while the samples with Si/Al ratios more than 7 have highly ordered mesoporous structure with crystal like morphology.
Chemistry and application of porous coordination polymers
Shimomura S., Horike S., Kitagawa S.
The porous coordination polymers (PCPs), as new functional microporous adsorbents consist of metal ions and organic ligands, have attracted the attention of chemists from the viewpoint of both scientific interest in the creation of regular nano-sized void spaces with unprecedented guest accommodation phenomena and commercial interest in their promising applications such as gas storage, molecular separation and in heterogeneous catalysis. The recent development in designing the porous framework has provided unprecedented gas sorption properties or selective guest entrapment by introducing various kinds of interaction sites; from van der Waals interaction to charge transfer interaction within the open framework.
Preparation and catalysis of nano-sized eetal (Pd,Pt) catalysts deposited on Ti-containing zeolite materials by a photo-assisted deposition (PAD) method
Mori K., Miura Y., Shironita S., Tomonari M., Mimura N., Yamashita H.
Nano-sized metal particles (Pt and Pd) can be highly deposited on Ti-containing zeolite materials (Ti-HMS and TS-1) under UV-light irradiation using a photo-assisted deposition (PAD) method. The nano-sized metals were deposited directly on the photo-excited tetrahedrally coordinated titanium oxide moieties within the frameworks. Characterization by XAFS and TEM analysis revealed that the size of metal particles depends on the preparation methods and that the smaller sizes of metal particles were formed on the photo-deposited catalysts compared to the conventionally prepared impregnated catalysts. These nano-sized metal catalysts are useful as efficient catalysts for the various reactions such as the oxidation of CO and the direct synthesis of H2O2 from H2 and O2 under an aqueous condition.
Natural gas purification with a DDR zeolite membrane; permeation modelling with maxwell-stefan equations
van den Bergh J., Zhu W., Groen J.C., Kapteijn F., Moulijn J.A., Yajima K., Nakayama K., Tomita T., Yoshida S.
The permeation of CO2, N2 and CH4 and their mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a very high selectivity for CO2 and a moderate selectivity for N2 over CH4 with good permeances. At a total pressure of 101 kPa and temperature of 225 K, the selectivity for CO2 was found to be over 3000 and 40 for N2 in a 50/50 feed mixture with CH4, both decrease with temperature. The N2/CH4 selectivity remains constant with pressure, while that for CO2/CH4 decreases. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The diffusivity of these permanent gases is strongly dependent on the loading in the membrane, severely complicating modelling work. A model developed by Reed and Ehrlich [1] could describe this phenomenon well for both the unary as the binary permeances. The feasibility of DDR membranes as applied to CO2 and N2 removal from natural gas is anticipated.
Application of modified β zeolite in the direct synthesis of LPG from syngas
Ge Q., Li X., Fujimoto K.
The application of Pd-β in the LPG (Liquefied Petroleum Gas) synthesis from syngas has been investigated, the results showed that there exists an synergistic effect between Pd-β and Pd-Zn-Cr in the LPG synthesis from syngas, the SiO2/Al2O3 ratio of Pd-β has an largely influence on the stability of Pd-Zn-Cr/Pd-β catalysts for syngas to LPG. As the SiO2/Al2O3 ratio increasing from 37 to 300, CO conversion decreases from 78.7% to 72.2%; however, the catalytic stability of Pd-Zn-Cr/Pd-β catalysts is largely improved. The reaction of LPG synthesis from synthesis gas over Pd-β/Pd-Zn-Cr hybrid catalyst follows the route: synthesis gas to LPG via methanol or DME.
Synthesis of well-ordered nanospheres with uniform mesopores assisted by basic amino acids
Yokoi T., Iwama M., Watanabe R., Sakamoto Y., Terasaki O., Kubota Y., Kondo J.N., Okubo T., Tatsumi T.
We applied basic amino acids in place of NH3 to the well-known Stöber method for preparing silica spheres; the hydrolysis and condensation reactions of tetraethyl orthosilicate were conducted in the presence of basic amino acids such as L-lysine and L-arginine. The obtained silica spheres, which are of uniform size of 12 nm, are well-ordered, forming a cubic closed pack (ccp) structure, Fm-3m space group. The arrangement of uniform spheres simultaneously creates intraparticle uniform mesopores of about 3 nm. We also succeeded in the preparation of exact carbon replica with uniform mesopores by using the silica nanospheres as a template. The results shown here are the first example of the arrangement of silica nanospheres assisted by simple biomolecules, leading to the development of a novel family of ordered mesoporous materials, which will open up a wide range of possibilities for the synthesis of spontaneously assembled nano-structured materials.
Structural design in the silicate framework of ordered mesoporous silica derived from kanemite
Kimura T., Tamura H., Tezuka M., Mochizuki D., Shigeno T., Kuroda K.
The silicate framework of ordered mesoporous silica KSW-2 was chemically designed and structurally stabilized by direct silylation of the mesostructured precursor using silylating agents such as octoxytrichlorosilane (C8H17OSiCl3) and octylmethyldichlorosilane (C8H17-(CH3)SiCl2). Depending on the molecular structures of the silylating agents, pure silica type and surface-modified type mesoporous materials can be obtained with the retention of the molecularly ordered framework because of the presence of the new silicate units strengthened by silylation, and the framework was thermally more stable.
