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21.
Yoshihiro Kubota Yusuke Nishizaki Hisanori Ikeya Masami Saeki Tetsunari Hida Sachiko Kawazu Michitaka Yoshida Hidekazu Fujii Yoshihiro Sugi 《Microporous and mesoporous materials》2004,70(1-3):135-149
Two types of organic–inorganic hybrid base catalysts are prepared. Organic-functionalized molecular sieves (OFMSs), particularly “amine-immobilized porous silicates”, are designed based on common idea to immobilize catalytic active sites on silicate surface. Silicate–organic composite materials (SOCMs), such as “ordered porous silicate–quaternary ammonium composite materials”, are the precursors of ordered porous silicates obtained during the synthesis. Both the OFMS and the SOCM are used as the catalysts for Knoevenagel condensation. Among the OFMSs, there is clear tendency that the use of molecular sieve with larger pore volume and/or surface area gives the product in higher yield. Aminopropylsilyl (AP)-functionalized mesoporous silicates such as AP-MCM-41 gives the product in high yield under mild conditions. No loss of activity is observed after repeated use for three times. The SOCMs are also active for the same reaction. The precursors of the mesoporous silicates are more active than those of microporous silicates. This material can be repeatedly used without significant loss of activity. High activity is not due to the leached species. The active sites of the SOCM catalysts are considered to be SiO− moieties located on the pore-mouth. Activity of the SOCM increases when the reaction is carried out without solvent, whereas decrease in activity of the OFMS is observed in the solvent-free system. 相似文献
22.
Rajib Bandyopadhyay Mahuya Bandyopadhyay Yoshihiro Kubota Yoshihiro Sugi 《Journal of Porous Materials》2002,9(2):83-95
AlPO4-5 and AlPO4-11 were synthesized by dry-gel conversion (DGC) method. Steam-assisted conversion (SAC) and vapor-phase transport (VPT) techniques were applied for this purpose. The synthesis was successful in presence of a certain minimum amount of external bulk water, without which the crystallization failed. Crystallization by VPT method was slower than corresponding SAC and HTS method. SAPO analogs of the samples, SAPO-5 and SAPO-11 were also synthesized by DGC method. Samples made by DGC methods had higher yield than the conventional hydrothermal synthesis (HTS); otherwise the samples showed similar characteristics as that made by HTS. XRD, SEM and N2-adsorption results showed high crystallinity and purity of the samples made by DGC, and 27Al MAS NMR spectra indicated the tetrahedral framework nature of Al. SAPO-5 and SAPO-11 were tested for their catalytic activity in isopropylation of biphenyl, and in terms of conversion and selectivity, SAPO-5 was found to be suitable for this application. 相似文献
23.
ihiro Kasuga † ‡ Tatsuya Inoue† Kenji Tsuji† Yoshio Ota† § Yoshihiro Abe † 《Journal of the American Ceramic Society》1995,78(1):245-247
High-strength calcium metaphosphate fibers for biomedical applications are extracted from crystallized products of calcium ultraphosphate glasses by aqueous leaching. In the present work, new types of porous ceramics with a skeleton composed of the crystalline fibers are prepared by heating the fibrous products extracted. The fibers in the ceramic are interlinked to each other by glassy phases formed during the heating. This porous material has a large porosity of >60%. The surface of the skeleton can be successfully converted into new calcium phosphate phases such as apatite by heating the porous material treated with a molten salt mixture of CaCl2 -Ca(NO3 )2 . 相似文献
24.
Taeko Izumi Yoshihiro Yagimuma Masanori Haga 《Journal of the American Oil Chemists' Society》1997,74(7):875-878
Enyzmatic amidation of the primary amines β-alanine ethyl ester and 3-aminopropionitrile with methyl laurate by means of immobilized
lipase (Candida antarctica lipase, CAL) resulted in the formation in good yield of N-lauroyl-β-alanine ethyl ester and 3-(N-lauroylamino)-propionitrile, respectively. When 3-amino-propionitrile was used as substrate, diisopropyl ether was a suitable
solvent. Changing the reaction temperature (12–80°C) did not affect the yields, and room temperature was a suitable temperature
for this reaction. In the investigation of reaction conditions, the use of equimolar amounts (5 mmol) of substrate and ester,
along with 0.5 g of CAL, in diisopropyl ether gave the best yield (99.3%) after 24 h of incubation at 24°C. The enzyme activity
in the amidation reaction did not decrease even after six uses. With β-alanine ethyl ester hydrochloride as substrate, diisopropyl
ether was unsuited as a solvent owing to the low solubility of the substrate in this solvent.
In this reaction, the best yield (82.0%) was attained by using dioxane as solvent. CAL achieved higher extents of amide synthesis
with long-chain than with short-chain ester substrates. The enzyme accepted only nonbulky primary amines as substrates. 相似文献
25.
Yoshihiro Hirata Kazuyoshi Sakeda Yumi Matsushita Kinji Shimada Yoshimi Ishihara 《Journal of the American Ceramic Society》1989,72(6):995-1002
Submicrometer SiO2 -Al2 O3 powders with compositions of 46.5 to 76.6 wt% Al2 O3 were prepared by hydrolysis of mixed alkoxides. Phase change, mullite composition, and particle size of powders with heating were analyzed by DTA, XRD, IR, BET, and TEM. As-produced amorphous powders partially transformed to mullite and Al-Si spinel at around 980°C. The compositions of mullite produced at 1400° and 1550°C were richer in Al2 O3 than the compositions of stable mullite solid solutions predicted from the phase diagram of the SiO2 -Al2 O3 system. Particle size decreased with increasing Al2 O3 content. The sintered densities depended upon the amount of SiO2 -rich glassy phase formed during sintering and the green density expressed as a function of particle size. 相似文献
26.
The crystal-growth process and growth conditions of β-alumina (Na2 O · Al2 O3 ) were investigated using the Na2 B4 O7 -Na3 AlF6 flux method. β-Alumina (electric fusion brick) was used as both nutrient and seed. Weight loss of the flux varied widely for various runs: ≅ 10 wt% of flux evaporated at 100 h, ≅ 17 wt% at 150 h, and 43 wt% at 600 h. When β-alumina crystal was grown, only 20 wt% Na2 B4 O7 was added to the Na3 AlF6 flux. The linear growth rates of the β-alumina single crystal grown by an Na3 AlF6 -20 wt% Na2 B4 O7 flux method at 1040°C and Δ t = 18°C were ≅ 1.0 × 10−3 mm/h ( a face) and ≅0.3 × 10−3 mm/h ( c face). The β-alumina single crystals grown were bounded by only c [001] and a [100] and were colorless and transparent. 相似文献
27.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
28.
Kazuhiko Takeuchi Taka-aki Hanaoka Takehiko Matsuzaki Matti Reinikainen Yoshihiro Sugi 《Catalysis Letters》1991,8(2-4):253-261
Vapor phase hydroformylation of ethylene was studied with silica-supported metal catalysts. A cobalt metal catalyst derived from Co2(CO)8 gave propanal and its derivatives in as high selectivity of about 36% as Rh/SiO2 catalyst under the reaction conditions of 1.1 MPa of a gas-mixture of ArCOC2H4H2 = 1333 at 423–503 K. On the other hand, conventional cobalt catalysts derived from cobalt nitrate, chloride, or acetate, and other noble metal catalysts (Pd/SiO2 and Ir/SiO2) produced mainly ethane. 相似文献
29.
Preparation of Aragonite Whiskers 总被引:10,自引:0,他引:10
Yoshio Ota Saburo Inui† Tetsushi Iwashita† Toshihiro Kasuga† Yoshihiro Abe† 《Journal of the American Ceramic Society》1995,78(7):1983-1984
A simple synthetic method for preparing aragonite whiskers has been developed. A suspension of CaCl2 -MgCl2 -Mg(OH)2 with pH ∼9 has been prepared by adding Ca(OH)2 to MgCl2 aqueous solution. CaCO3 whiskers (aragonite phase) have been prepared easily by blowing CO2 -containing gas into the suspension. The whiskers have high aspect ratios ranging from 20 to 80 with diameters of 0.5–1 μm . 相似文献
30.
Masayuki Nogami Naoya Hayakawa Naoya Sugioka Yoshihiro Abe 《Journal of the American Ceramic Society》1996,79(5):1257-1261
Samarium ions (Sm2+ ) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2 O-Al2 O3 SiO2 synthesized by the hydrolysis of Si(OC2 H5 )4 , Al(OC4 H9 )3 , CH3 COONa, and SmCl3 ·6H2 O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2 O3 -SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2 O2 -SiO2 glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min. 相似文献