Synthesis of Sn-Incorporated Folded Sheets Mesoporous Materials (Sn-FSM-16)

Sn-incorporated folded sheets mesoporous materials (Sn-FSM-16) with various contents of Sn were synthesized by using a mixture of water glass, SnCl₄ and NaOH as starting materials. Hexadecyltrimethyl-ammonium chloride (surfactant) was used to intercalate into the layered silicate. The reaction process was followed by measurements of XRD patterns of intermediates. The Sn-FSM-16 was formed via the following mechanism: (1) layered silicates such as - - and -Na₂Si₂O₅ were formed as intermediates by the calcination of the mixture of the starting materials; (2) the surfactant was intercalated into the layered silicates; (3) the surfactant-silicate complex with hexagonal structure was obtained as a precursor of Sn-FSM-16; (4) the precursor was calcined to decompose the surfactant in the interlayer and was changed to Sn-FSM-16. The structural aspect of Sn in Sn-FSM-16 was studied by XPS profiles of Sn 3d _5/2 and Si_2p, ²⁹ Si MAS NMR and FTIR. The content of Sn in Sn-FSM increased with increasing concentrations of both Sn and NaOH in the starting materials. The surface area of Sn-FSM-16 decreased with an increase of Sn content in Sn-FSM (1160–620 m²/g).     

Vapor phase hydroformylation of ethene over Co/SiO2 promoted by noble metals: dynamic in situ diffuse reflectance FT-IR study of surface species

An in situ diffuse reflectance FT-IR technique was employed to investigate the active surface species and the reaction mechanism of the oxygenate formation in the vapor phase hydroformylation of ethene on Co/SiO₂ promoted with various noble metals such as Ir, Rh, Pt, Re, Ru, and Pd. Co(A)/SiO₂ and Ir(CO)/SiO₂ which were derived from cobalt(II) acetate and Ir₄(CO)₁₂, respectively, were quite inactive in the reaction, and showed only quite small peaks of adsorbed CO under the conditions of 1.1 MPa of C₂H₄/CO/H₂ at 298 K. In contrast, Co(A)-Ir(CO)/SiO₂, which were very active in the reaction, exhibited strong absorption bands of linear and bridged CO species. At 423–463 K, propanal adsorbed on the catalyst and acyl species which is suggested as the intermediate for the formation of propanal were also observed on this catalyst. By exposing CO preadsorbed on this catalyst to C₂H₄/H₂ at 289 K and 0.1 MPa, the intensity of the linear CO band decreased, and the bands of propanal and acyl species emerged simultaneously, whereas that of the bridged CO band remained constant after the initial drop. These results suggested that the oxygenates are formed via the CO insertion into adsorbed ethyl species, and linear CO species plays a major role in the CO insertion on these noble metal-promoted cobalt catalysts.     

Formation of Small-Sized CdSxSe1-x Crystals in Sol-Gel-Derived SiO2 Glasses

Silica glasses doped with small-sized CdS_x-Se_1-x crystals were prepared by the sol-gel method. Gels synthesized by the hydrolysis of Si(OC₂H₅)₄, in the presence of CdSeO₄ with NH₄SCN dissolved in HNO₃ or NH₄OH, were heated in H₂-N₂ atmosphere. The pH value of solutions for CdSeO⁴ and NH⁴SCN primarily determined the fraction of anions in CdS^xSe^1-x crystals. The anion content in crystals was dependent on the pH value of the solvent and/or heat-treatment temperature, and the sulfur fraction changed from 0.1 to 0.6. The optical absorption spectra were red-shifted as the selenium content and the crystal size increased, and the emission spectra showed a sharp band near the absorption edge position and a broad tail extending into the long wavelength. The optical band gap energies increased reciprocally proportional to the square of the crystal size.     

Synthesis and properties of N,N'-unsymmetrical dialkyl-3,4:9,10-perylenebis(dicarboximide)s

N,N'- Unsymmetrical dialkyl-3,4:9,10-perylenebis(dicarboximide)s (in which alkyl = methyl, ethyl, propyl, butyl, isobutyl, pentyl, hexyl and octyl) were prepared by the condensation of N-alkyl-3,4:9,10-perylene-tetracarboxylic monoanhydride monoimide with the appropriate alkyl-amines. The properties of these derivatives as pigments were tested and their thermal stability measured.     

Characterization of highly active silver catalyst for NOx reduction in lean-burning engine exhaust

A new Ag/Al₂O₃ catalyst for removing NOx in lean exhaust gas was developed. Oxidized Ag/Al₂O₃ catalyst is highly active for reduction of NOx with ethanol and propene, whereas reduced Ag/Al₂O₃ catalyst is less active for these reactions. Selectivity to N₂ is also high on the oxidized Ag/Al₂O₃ compared to that on the reduced Ag/Al₂O₃. XRD and SEM studies of these two types of Ag catalysts suggest that oxidation induces an interaction between Ag and the support, where the particles are grown in large size. In contrast, the metallic Ag particles are finely dispersed by the reduction process. Although dispersion of Ag particles is decreased by the oxidation process, the catalytic activity is increased. This suggests that the Ag-alumina sites created in the high temperature oxidizing environment are active in catalytic reduction of NOx. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of activated carbon pore structure on oxygen reduction at catalyst layers supported on rotating disk electrodes

Carbon materials are often used as catalyst supports, and for catalysts in electrodes of a polymer electrolyte fuel cell, carbon black has been used. Recently, it was found, however, that activated carbon could replace carbon black and besides, significantly improve the activity of the electrode catalyst layer for oxygen reduction. In the present study, to optimize the pore structure of activated carbon for further activity improvement, the influence of the pore structure on the activity was investigated using activated carbon of various specific surface areas and mean pore diameters. A catalyst layer was formed from activated carbon loaded with platinum and a polymer electrolyte. The activity of the layer was measured in an oxygen-saturated perchloric acid solution, supporting the layer on a rotating glassy carbon disk electrode. We found that increases in the specific surface area and mean pore diameter increased the activity and that the latter was more effective than the former mainly due to the enhanced mass-transfer in the pores; the catalyst layer formed from activated carbon with the largest mean pore diameter was the most active. Unless pores excessively develop and lose connections between particles, a large pore diameter is therefore desired for the fuel cell electrodes.     

Elevated temperature instrumented Charpy impact of a sintered silicon carbide

A commercially available, densely sintered alpha silicon carbide was tested in air from room temperature to 1700°C using a modified instrumented pendulum unit and standard Charpy size test specimens. The resistance heated silicon carbide specimens exhibited only elastic behavior, even at 1700°C. A compliance analysis of the test revealed a linear elastic decrease of the absorbed impact energy and also a decrease of the fracture stress of the silicon carbide with increasing temperature.     

Organic–silicate hybrid catalysts based on various defined structures for Knoevenagel condensation

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.     

Lysozyme requires fluctuation of the active site for the manifestation of activity

Mutations around His15 which lie far away from the active site,stimulated glycol chitin activity of lysozyme at physiologicaltemperature. Del-Argl4Hisl5 lysozyme, a mutant lysozyme whoseArgl4 and Hisl5 were deleted together, and has the highest activityamong these mutant lysozymes, had a similar binding abilityto a trimer of N-acetyl-glucosamine, a substrate analogue, relativeto native lysozyme. This suggests that the increased activitywas due to an increased k_cat in the catalysis reaction. TheH-D exchange rate of the N-1 proton in the Trp63 which is locatedin the active site cleft, was enhanced in the Del-Argl4Hisl5lysozyme, while 2-D proton NMR analysis revealed no conformationalchange around Trp63. We conclude that some sort of fluctuationat the active site might be required for the manifestation ofactivity. This theory is supported by the finding that the Del-Argl4Hisl5lysozyme showed a shift in temperature dependency of activityto lower temperatures compared with that of native lysozyme.     

Preparation of Porous Ceramics with Calcium Metaphosphate Fiber Skeleton for Biomedical Use

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.