論文

Recently, microwave (MW) heating has been applied to chemical reactions instead of conventional heating because heating only catalysts by MW radiation is more energy-efficient than heating reaction systems by conventional heating. However, zeolites, which are widely used as catalysts in the chemical industry, can hardly be heated by MW radiation. Here, zeolite catalysts suitable for MW heating were prepared by filling carbon in the interlayer-expanded micropores of MWW-type zeolites. The carbon in the pores was readily heated by MW radiation. When the catalyst was heated in a nitrogen stream by MW radiation at 50 W of consumed electric power, the temperature reached 450 °C for 300 s. However, the temperatures of the MWW-type zeolite and the physical mixture of the MWW-type zeolite and graphite powder were 140 °C and 260 °C, respectively. This indicated that the carbon-filled interlayer-expanded MWW was suitable for MW heating. The methylation of toluene with methanol catalyzed using a proton-type C@expanded MWW by MW heating proceeded at a lower reaction temperature, compared with that of the methylation catalyzed using the physical mixture of the MWW-type zeolite and graphite. This indicated that the carbon-incorporated catalysts were suitable for MW heating and that the internal temperature of the catalyst particles was higher than the external temperature. This enhanced the shape selectivity because the reaction preferentially proceeded inside the pores.

TON-type zeolite crystals in the shape of short needles were synthesized using inhibitors of crystal growth along the [001] direction. When fluoride was used as a mineralizer, bulky amines incorporating structure-directing agents acted as inhibitors, while nonionic surfactants were more effective as inhibitors for decreasing the crystal length of TON-type zeolite. The amount of surfactant adsorbed on the zeolite increased with the surface area of the face containing pore mouths. This indicates that the surfactant was trapped in the pore mouths to inhibit crystal growth along the long axis of the needle-shaped crystals. By microscopic observation of the crystals, we confirmed inhibition of crystal growth by adsorption of the surfactant. After adsorption of Nile red, a lipophilic stain that is intensely fluorescent in surfactants, on as-synthesized zeolite, only the edges of the needle-shaped crystals were luminous, also indicating adsorption of the surfactant in pore mouths. When hydroxide was used as a mineralizer, the bulky amines acted as inhibitors. Nonionic surfactants, however, did not work. We used the obtained shorter crystals of TON-type zeolites as catalysts for hydroisomerization of n-tetradecane. Use of the shorter crystals improved the selectivity for skeletal isomerization.

Vanadyl ion-containing VAPO-5 and CoAPO-5 are prepared by contact with a vanadyl sulfate solution or by impregnation with aqueous vanadyl oxalate and characterized by powder X-ray diffraction, electron spin resonance spectroscopy, and temperature-programmed reduction (TPR). Treatment of VAPO-5 with vanadyl ion results in incorporation of up to 1.0 wt% total vanadium into the AFI framework by filling lattice vacancies. At vanadium contents above ca. 1 wt%, extraframework vanadium is also obtained. TPR results show that framework vanadium can be reduced by hydrogen at a lower temperature than extraframework vanadium and vanadium in bulk V2O5. Oxydehydrogenation of propane over VAPO-5 samples reveals that framework vanadium is the most active and selective species for propylene formation (at 400 degrees C and 5% conversion, the selectivity is 72%); extraframework vanadium species are less active and selective. (C) 2000 Academic Press.

Phenyltrichlorogermane was synthesized with high, selectivity, 96%, from elemental germanium, tetrachlorogermane, and chlorobenzene using no catalyst, almost all germanium and tetrachlorogermane being converted. Dichlorogermylene was formed as a reaction intermediate by the reaction of germanium with tetrachlorogermane and inserted into the C-Cl bond of chlorobenzene to yield phenyltrichlorogermane.

Polyethylene glycol (PEG) was impregnated on a palladium metal supported on silica gel and used in a catalyst for hydrogenation of benzaldehydes. In the vapor-phase flow reaction, the PEG modification improved catalytic activity and selectivity for a partially hydrogenated product, benzyl alcohol. In isoprene hydrogenation, selectivity for partially hydrogenated products, monoenes, was also enhanced. X-ray photoelectron spectroscopy (XPS) analysis of the modified catalysts revealed that the modification with PEG makes the palladium surface negatively charged, possibly leading to an increase in the selectivity for the partially hydrogenated product caused by enhancement of its desorption from the surface. In the liquid-phase hydrogenation of benzaldehyde, the PEG modification also increased the selectivity for benzyl alcohol. © 2010 Elsevier Inc. All rights reserved.

Polydimethylsiloxane terminated by a methyl group was almost completely depolymerized in the mixture of dimethyl carbonate (DMC) and methanol using alkali metal halide catalysts to form dimethoxydimethylsilane (DMDMS) and methoxytrimethylsilane (MTMS) monomers. The various alkali metal halides tested as catalysts gave the same monomer yield. The depolymerization rate depended on the kind of alcohol but not on dialkyl carbonate. The results indicate that the siloxane bond is cleaved by methanol attack to form the corresponding monomers together with water and that dimethyl carbonate reacts with water formed as a byproduct to give methanol, whose amount is the same as that of the methanol consumed for cleavage of siloxane bonds. Therefore, dimethyl carbonate, not methanol, acts as the depolymerization reagent in the apparent reaction. Depolymerization of poly(methylphenylsiloxane-ran-dimethylsiloxane) and poly(methylvinylsiloxane-ran-dimethylsiloxane) with dimethyl carbonate in methanol using potassium fluoride catalyst also proceeded to obtain dimethoxymethylphenylsilane and dimethoxymethylvinylsilane, respectively, together with dimethoxydimethylsilane and methoxytrimethylsilane from polydimethylsiloxane parts. Silicone rubber containing silica as an additive was also depolymerized to form dimethoxydimethylsilane together with a small amount of tetramethoxysilane formed from silica additive. Therefore, the depolymerization with DMC using alkali metal salt catalyst can be counted on for recycling silicone waste. (C) 2003 Elsevier B.V. All rights reserved.

Aggregates of zeolite nanoparticles were linked together with polypropylene oxide or polydimethylsiloxane polymer chains, and were used as catalysts for liquid-phase reactions. The polymer-linked catalysts showed high catalytic activity in esterification of acetic acid with 1-propanol and hydrolysis of ethyl acetate, and were readily separated from reaction mixtures by decantation. Moreover, the linkage with the polymer chains enhanced shape selectivity in esterification of acetic acid with cyclohexanol and dehydration of 1-phenylethanol because of passivating the external acid sites of the zeolite with the polymer. © 2013 Elsevier B.V. All rights reserved.

The reactions of silicon with ethanol, propanols and butanols were studied using copper(I) chloride as the catalyst. Primary alcohols reacted with silicon, while secondary and tertiary alcohols did not. The reactions of silicon with ethanol, 1-propanol, and 1-butanol gave high silicon conversions of 95, 85, and 77%, respectively, at 513 K without heating treatment of the silicon-catalyst mixture. Under these conditions, the selectivities for trialkoxysilanes were very high (>99%). The pretreatment of the silicon-catalyst mixtures at high temperatures (i.e., 723 K) to facilitate the formation of Cu3Si Phase is not favorable for the reactions: Both the silicon conversion and the selectivity for trialkoxysilane are sharply depressed. Metallic copper is easily formed on the silicon surface during the reactions after high temperature pretreatment. The metallic copper catalyzes the dehydrogenation of alcohols to aldehydes, which inhibit the silicon-alcohol reactions. It also catalyzes the reaction of trialkoxysilane with alcohol to give tetraalkoxysilane. This brings about the decrease in the selectivity for the trialkoxysilane. However, the high silicon conversion together with high selectivity was obtained by adding thiophene or propyl chloride, which is a poison for copper catalysts, to the alcohol feed. Though 2-propanol does not react with silicon, dimethoxyisopropoxysilane and methoxydiisopropoxysilane were formed appreciably when 2-propanol was fed to the silicon together with methanol. This phenomenon was discussed in relevance of the mechanism of the silicon-alcohol reactions. (C) 1994 Academic Press, Inc.

When copper(I) chloride was used as a catalyst in the reaction of silicon with phenol, a high selectivity for triphenoxysilane (HSi(OPh)(3)) (94%) was obtained, the other product being tetraphenoxysilane (Si(OPh)(4)). Addition of a small amount of propyl chloride to the feed for poisoning metallic copper enhanced the selectivity for HSi(OPh)(3) without affecting the rate of silicon consumption. This result indicates that HSi(OPh)(3) is an exclusive primary product and that Si(OPh)(4) is formed by the secondary reaction between HSi(OPh)(3) and phenol. The reaction mechanism involving surface silylene intermediate is proposed for the formation of HSi(OPh)(3) as the sole primary product. The intermediacy of surface silylene was confirmed by adding ethylene in the silicon-phenol reaction to give rise to the trapped product ethyldiphenoxysilane, obtained in a 5.8% selectivity.

TON-type zeolites with a core-shell structure were synthesized by crystal overgrowth of an aluminum-free TON-type zeolite on an aluminum-containing TON-type zeolite in the presence of fluoride ion, which was used as a mineralizing reagent to restrain the formation of defects. The core-shell structured zeolite showed greater selectivity for skeletal isomerization in tetradecane hydroisomerization because the acid sites on the external surface of needle-shaped crystals were passivated to inhibit cracking. Breaking the needle-shaped crystals of the core-shell structure to create shorter crystal pieces effectively enhanced the catalytic activity and selectivity for isomerization because new pore entrances were formed. (c) 2013 Elsevier B.V. All rights reserved.

Ordered porous materials such as zeolites and ordered mesoporous silicas have important physical characteristics based on their high surface area and well-defined pore size. Control of the structure or shape of the ordered porous materials will provide new functions. This review focuses on core-shell structure; especially fabrication methods of core-shell structured zeolites with minimal defects are introduced. As an example of applications, MFI and TON-type zeolites with core-shell structure used as catalysts have high shape selectivity in the methylation of toluene with methanol and skeletal isomerization of tetradecane, respectively. As another application, synthesis of hollow porous materials from core-shell porous materials is also described. Decomposition of silica with dimethyl carbonate catalyzed by an alkali metal salt impregnated in the core was an effective method for selective removal of the core from the core-shell structure. Hollow porous materials show promise as vessels for drug delivery, catalyst vessels and microreactors.

Hollow silica spheres with radially oriented mesopores were synthesized by treating core-shell structured mesoporous silica spheres (pure silica core and propyl group-grafted silica shell) with an ammonia solution in the presence of alkyltrimethylammonium chloride. The pure silica cores dissolved in the basic solution but the propyl groups and the surfactant adsorbed on the shells protected the mesopore walls in the shells from the basic solution. Treating mesoporous silica spheres with three-layered structures (silica with grafted propyl groups, pure silica, and then silica with grafted propyl groups) led to mesoporous spheres with rattle structures being formed. The hollow and rattle-type spheres acted as microreactors when they were added to two-phase reactions, halogen exchange reaction, hydroformylation and esterification, and the reaction rates were increased. Stirring caused the hollow spheres containing the aqueous phase to be transferred into the organic phase, causing the reaction rate to be increased. Modifying the mesopore walls with phenyl groups to make the spheres highly hydrophobic increased the amount of spheres that was present in the organic phase, increasing the reaction rate. A higher reaction rate was achieved using hollow spheres than that using non-hollow mesoporous silica spheres, indicating that the hollow structure was an important factor in increasing the reaction rate.

The reaction of methanol with silicon was studied using various copper compounds other than the halides. Copper(II) acetate and copper(I) oxide gave high silicon conversions (82%) though the selectivities for trimethoxysilane were low (<19%). The selectivity was appreciably improved by addition of a small amount of thiophene or propyl chloride to the methanol feed.

The reaction of hydrous titanium dioxide (TiO2 . nH(2)O, n = 0.15-1.23) and dialkyl carbonates at 453-573 K offers a convenient synthetic method for titanium tetraalkoxides which are free from chlorine-containing impurities. Thus, hydrous titanium dioxide was almost completely converted into Ti(OEt)(4) by its reaction with diethyl carbonate at 493 K for 16 h. The reaction proceeded faster in the presence of a sodium hydroxide catalyst. From the hydrous titanium dioxide and dipropyl carbonate, Ti(OPrn)(4) was obtained in a high yield.