Shozi Mishima

EFFECT OF CRYSTALLITE SIZE ON THE CATALYSIS OF ALUMINA-SUPPORTED COBALT CATALYST FOR STEAM REFORMING OF ETHANOL

The selectivity for steam reforming of ethanol on alumina-supported cobalt catalysts is closely related to the crystallite size of cobalt, which varies the strength of ethanol adsorption.

Conversion of ethanol to acetone over zinc oxide-calcium oxide catalyst : Optimization of Catalyst Preparation and Reaction Conditions and Deduction of Reaction Mechanism

Abstract The conversion of ethanol to acetone in the presence of water vapour was studied in order to find the optimum catalyst composition, catalyst calcination temperature and reaction conditions and to deduce the reaction mechanism. A catalyst containing 10 mol-% calcium oxide gave the best ethanol conversion and acetone selectivity. This catalyst, calcined at 773 K, had the largest BET surface area and gave 100% ethanol conversion and 91% acetone selectivity at a reaction temperature of 674 K. A feasible mechanism is proposed that involves oxidation of adsorbed acetaldehyde by surface hydroxide ion as the rate-determining step.

A highly active and highly selective oxide catalyst for the conversion of ethanol to acetone in the presence of water vapour

In the presence of water vapour and a suitable catalyst, ethanol is converted to acetone rather than to ethylene and acetaldehyde. In order to develop an appropriate catalyst for this reaction, steady-state catalytic activities and selectivities were studied for 24 oxide catalysts. It was found that the acetone selectivity is high on a catalyst having both surface acidity and basicity, suggesting that the acetone formation is an acid-base bifunctional catalytic reaction. Iron oxide is superior to the other oxides studied here in both conversion and acetone selectivity. The superiority is greatly enhanced by mixing iron oxide with zinc oxide. The preparation method for the iron–zinc mixed oxide catalyst was also studied and it was found that the optimal composition is Zn/(Fe + Zn)= 0.1–0.4 and that the optimal condition for calcination is 773 K for 3 h. The catalyst gave 100% ethanol conversion and 94% acetone selectivity at a reaction temperature of 713 K. It is initially a mixture of Fe2O3 and ZnO but is converted to a spinel type compound, ZnFe2O4, during the reaction. The optimal reaction temperature was determined to be 713 K, and at this temperature, the acetone yield decreased by 34% after a time of 24 h.

Characterization of active sites working on FSM-16 during the vapor-phase Beckmann rearrangement of cyclohexanone oxime

Abstract The behaviors of e-caprolactam, cyclohexanone oxime and Beckmann rearrangement by-products on FSM-16 and Al 2 O 3 /FSM-16 have been investigated in detail by means of TPD and reactions in the presence of organic acids and pyridine. The TPD spectra on FSM-16 of e-caprolactam, cyclohexanone oxime, Beckmann rearrangement by-products and mixtures of by-products can be explained by postulating that there are four kinds of active sites, i.e. two kinds of nitrile formation sites (Sites A and R), a cyclohexanone formation site (Site B) and a nitrile adsorption site (Site α). The TPDs of cyclohexanone oxime adsorbed on Al 2 O 3 /FSM-16 in the presence and absence of water vapor suggest that the presence of water accelerates the formation of cyclohexanone on Site B. Addition of acetic acid suppresses conversion of e-caprolactam to nitriles, and that addition of pyridine has no effect on the TPD spectrum. Addition of acetic acid to the reactant during the Beckmann rearrangement on Al 2 O 3 /FSM-16 improved the e-caprolactam yield and catalyst’s life.

Block copolymer-mediated synthesis of gold nanoparticles in aqueous solutions: Segment effect on gold ion reduction, stabilization, and particle morphology

We report here on the segment effects of poly(ethylene oxide)-containing block copolymers (PEO-BCP) on the reduction activity for tetrachloride gold(III) ([AuCl(4)](-)), interfacial activity for gold surface, colloidal stability, and morphology of gold nanoparticles formed in aqueous solutions. In particular, the effects of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), polyethylene (PE) segments and amino group (NH(2)) on the rate of [AuCl(4)](-) reduction, adsorption of PEO-BCP onto gold surface, colloidal stability, and morphology of gold nanoparticles formed in aqueous solutions were examined using a poly(ethylene oxide)-poly(propylene oxide) triblock copolymer (PEO-PPO-PEO, Pluronic L44), an amino-terminated poly(ethylene oxide)-poly(propylene oxide) block copolymer (PEO-PPO-NH(2), SURFONAMINE® L-207), a poly(ethylene oxide) homopolymer (PEO, poly(ethylene glycol)2000), and a polyethylene-poly(ethylene oxide) block copolymer (PE-PEO). We found that the reduction activity of PEO-BCP for [AuCl(4)](-) became higher with the order of PEO-PPO-NH(2)<PE-PEO<PEO<PEO-PPO-PEO. The interfacial activity (affinity) of PEO-BCP for gold surface increased with the order of PEO<PE-PEO<PEO-PPO-PEO≪PEO-PPO-NH(2). Consequently, the colloidal stability of gold nanoparticles formed in aqueous PEO-PPO-NH(2) solutions was extremely high compared with that in PEO, PEO-PPO-PEO, and PE-PEO solutions. In addition, the size of gold nanoparticles formed in aqueous PEO-PPO-NH(2) solutions was much smaller than that in aqueous solutions of PEO-PPO-PEO, PEO or PE-PEO.

Chemically stable magnetic nanoparticles for metal adsorption and solid acid catalysis in aqueous media

We have developed a magnetically collectable, reusable adsorbent and a catalyst for concentrating heavy metal ions in acidic aqueous solutions and solid acid catalysis in aqueous media. Chemically stable, magnetic rattle-type core–shell particles, comprising metallic cobalt nanoparticles in hollow silica microspheres, were prepared by the sol–gel reaction of alkylsilyl trichlorides around water droplets in a water-in-oil emulsion. Sulfonic groups were immobilized on the external surface of the core–shell particles through silylation with 3-mercaptopropyl(trimethoxysilane) and subsequent oxidization of the thiol groups by nitric acid. The sulfonic groups acted as adsorption sites for Zn and Pb ions under acidic conditions and as catalytically active sites for the hydrolysis of ethyl acetate in aqueous media. The enclosed Co was not eroded during the regeneration of the adsorbent/catalyst by 1 M HCl. The chemical stability arose from the dense non-porous shell, which prevents the passage of solvents.

Effects of Si−Al composition on the fluorescence spectra of 1-naphthol during the sol-gel-xerogel transitions

A systematic study has been carried out on the characteristic changes in the fluorescence spectra of 1-naphthol doped in the sol-gel-xerogel transition systems comprised of tetraethyl orthosilicate and diisobutoxyaluminium triethylsilicate catalyzed by a small amount of HCl, NH4OH, as well as under uncatalyzed conditions. In the systems containing large amounts of silicon, the fluorescence of 1-naphthol shifts to the red (a predominant emission from the 1La state) during the first stage of the reaction. This red shift indicates an increase in the polarity of the matrix surrounding 1-naphthol. In the second stage of the reaction, the spectrum shifts to the blue (a predominant emission from the 1Lb state), reflecting an increase in the micro-viscosity around 1-naphthol. In the systems containing relatively large amounts of aluminum, however, the spectrum just after mixing shows a larger red shift than that originating from the 1L2 emission. This large red-shifted fluorescence reflects the formation of a complex between 1-naphthol and the −O−Al−O−Si−O-network. The spectrum then shifted to the blue. The spectral behaviours observed indicate that there is a large and dynamic molecular-level change in the physicochemical properties of the matrix surrounding the 1-naphthol molecules during the sol-gel-xerogel transitions of the systems while the gelation phenomenon reflects macroscopic inflexibility although it is completely different from the restriction of movement at the molecular level.

Relation between the formation constant and the local structure of various bases and reference acids for the 1 : 1 hydrogen-bond complexation in aprotic solvents

For the 1 : 1 hydrogen-bond complexation of various bases against reference acids in aprotic solvents, the formation constant has been correlated with the local structure of acids and bases by regarding a base or an acid as composed of two local structural units, a functional group and a residual moiety. The following equation has been introduced to correlate log K, where K is the formation constant with the local structures: log K=(ηy+ηx)ωbωa+ log K0 where ηy and ηx represent the nature of the functional group of the base and acid, respectively, ωb and ωa represent the electronic effects of the residual moiety of the base and acid, respectively, and log K0 is a constant.Family-independent and -dependent behaviour observed for log K of 26 bases against p-fluorophenol, phenol and 5-fluoroindole in CCl4 are reasonably interpreted by applying the above equation. Formal ωb values of the bases have been evaluated. It has been pointed out that Maria–Gals angle θ which represents the electrostatic: covalent ratio of hydrogen bonding reflects the nature of the functional group of reference acids, as well as ηx.

Titania/CnTAB Nanoskeleton as adsorbent and photocatalyst for removal of alkylphenols dissolved in water.

We report here on the removal of alkylphenols (phenol, 4-n-propylphenol, 4-n-heptylphenol and 4-nonylphenol) dissolved in water using the composite particles of nanocrystalline titania and alkyltrimethylammonium bromide (CnH2n+1N(CH3)3Br, CnTAB; n=12, 14, 16 and 18) (named as TiO2/CnTAB Nanoskeleton) as adsorbents and photocatalysts. In particular, the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton in water was investigated in terms of hydrophobic interaction between alkylphenols and CnTAB, surface area, pore structure and crystal size of TiO2/CnTAB Nanoskeleton. We revealed that CnTAB incorporated in the TiO2/CnTAB Nanoskeleton promotes the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton due to the hydrophobic interaction between alkylphenols and CnTAB. On the other hand, the surface area, pore structure and crystal size of TiO2/CnTAB Nanoskeleton did not affect the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton. We also found that the alkylphenols dissolved in water were completely removed by the combination of adsorption and photocatalytic degradation by the TiO2/CnTAB Nanoskeleton under UV irradiation. These results prove that the TiO2/CnTAB Nanoskeleton acts as in tandem an adsorbent and a photocatalyst for removal of alkylphenols dissolved in water.

Absorption and fluorescence spectra of 9-anthrol and its chemical species in solution

The absorption, fluorescence, and fluorescence-excitation spectra of 9-anthrol (and/or anthrone) have been observed in various solvents, one of which includes a silicon-aluminium ester (diisobutoxyaluminium triethyl silane[(OBu)2−Al−O−Si−(OEt)3 SAE]). The fluorescence spectra of 9-anthrol shows peak wavelengths at 442 nm in benzene, 454 nm in methanol, 539 nm in triethylamine, and 550 nm in basic solution, which can be assigned to a neutral, a hydrogen-bonded neutral, an ion pair, and an anionic species of 9-anthrol, respectively. In ethanol solution including SAE, on the other hand, a new fluorescence peak appears at 473 nm. This new band originates from a complex formed between 9-anthrol and SAE. The excited-state ion pair is formed through the hydrogen-bonded form in water and the complex form in triethylamine. CNDO/S calculations support the experimental results.