Teruoki Tago

Nickel thin films prepared by chemical vapour deposition from nickel acetylacetonate

Nickel thin films were prepared by a low-temperature atmospheric-pressure chemical vapour deposition method. The raw material was nickel acetylacetonate. At a reaction temperature above 250 °C, polycrystalline nickel films can be obtained by hydrogen reduction of the raw material. The resistivity (8.1–13.3 μΩ cm) of the film was close to that of bulk nickel.

Preparation of monolithic SiO2–Al2O3 cryogels with inter-connected macropores through ice templating

Macroporous monoliths of SiO2–Al2O3 cryogels were prepared. Macropores were generated by using ice crystals as the template, while the walls which surround the macropores were tailored as porous cryogels by freeze drying. Macropores and walls formed honeycomb-like structures, which were confirmed from scanning electron microscopy images of cross-sections of the samples. It was confirmed that the sizes of the macropores and the wall thicknesses were respectively in the ranges of 10–20 µm and 200–500 nm. Al mapping analysis by energy dispersive X-ray diffractometry showed that Al atoms were homogeneously dispersed throughout the samples without local aggregation. Moreover, Raman spectroscopy and 27Al NMR spectroscopy indicated that Al atoms were incorporated into the silica framework by forming an Al–O–Si polymeric network. Nitrogen adsorption–desorption measurements indicated that the walls were micro/mesoporous with high BET surface areas (>700 m2 g−1) and large pore volumes (>0.45 cm3 g−1). Moreover, NH3-TPD measurements revealed that the samples had acid sites, which allowed this material to be used as a solid acid catalyst.

Germanium‐ and silicon‐doped indium‐oxide thin films prepared by radio‐frequency magnetron sputtering

Indium oxide (In2O3) thin films doped with either germanium or silicon were prepared by using a radio‐frequency magnetron sputtering method. The target was the In2O3 powder mixed with either Ge or Si powder. The resistivities of the films were compared with that of the film doped with tin (ITO). The Ge and Si dopings yielded lower carrier concentrations and higher Hall mobilities compared to those for Sn doping, and they gave different dependencies of resistivity on atomic ratio. The minimum resistivity of the films doped with Ge was nearly equal to that of ITO.

Synthesis of silica-coated rhodium nanoparticles in reversed micellar solution

Silica (SiO2)-coated rhodium (Rh) nanoparticles were prepared using a water-in-oil microemulsion of polyoxyethylene (15) cetyl ether, cyclohexane and water. SiO2-coated Rh nanoparticles were obtained by hydrolyzing metal alkoxide (tetraethylorthosilicate, TEOS) in the solution containing Rh complex nanoparticles followed by thermal and reduction treatments. In the SiO2-coated Rh nanoparticle, a Rh particle with an average diameter of 4.1 nm was located nearly at the center of each spherical SiO2 particle. The SiO2 layer was approximately 15 nm thick. Since the Rh particle was wholly surrounded by SiO2, the Rh particle of the SiO2-coated Rh nanoparticle exhibited an extremely high thermal stability. Furthermore, the porous structure of the SiO2 layer could be controlled by the hydrolysis conditions of TEOS.

Effects of Rh content on catalytic behavior in CO hydrogenation with Rh–silica catalysts prepared using microemulsion

Rh–silica catalysts having the same physical parameters despite their different Rh contents were prepared using water‐in‐oil (w/o) microemulsions, and the effects of Rh content on the catalytic behavior were investigated in the hydrogenation of carbon monoxide. It was found that both the product selectivity and the turnover frequency changed dramatically with the Rh content. The selectivity to C2+ oxygenated compounds increased with increasing Rh content, while the selectivity to hydrocarbons and the turnover frequency decreased.

Kinetics of the catalytic cracking of naphtha over ZSM-5 zeolite: effect of reduced crystal size on the reaction of naphthenes

The catalytic cracking of model naphthenes (cyclohexane and methylcyclohexane) over ZSM-5 zeolites of different crystal sizes (macro- and nano-ZSM-5) was examined at reaction temperatures ranging from 748 to 923 K under atmospheric pressure, focusing on the associated reaction rate constants and activation energies. The catalytic cracking was found to follow first-order kinetics with respect to the naphthene concentrations and the activation energies for cyclohexane and methylcyclohexane cracking over nano-ZSM-5 were determined to be 119 and 116 kJ mol−1, respectively. In order to elucidate the rate-limiting step in the cracking process, the Thiele modulus and the effectiveness factor obtained from cracking over the two ZSM-5 zeolites were evaluated. Cracking with nano-ZSM-5 proceeded under reaction-limiting conditions, whereas the reaction over macro-ZSM-5 at 923 K took place under transition conditions between reaction- and diffusion-limiting. Nano-ZSM-5 was applied to the catalytic cracking of a model naphtha and the results demonstrated that this catalyst was both effective and stable and generated a high yield of light olefins.

n-ヘキサン接触分解による低級オレフィン選択合成におけるMFI型ゼオライトの結晶サイズとSi/Al比の影響

Light olefins are important basic raw materials for the petrochemical industry, and demand for light olefins such as ethylene and propylene has been increasing every year1),2). Light olefins have been mainly produced by thermal cracking of naphtha, which gives yields of ethylene and propylene of approximately 25 % and 13 %, respectively3)~5). However, the naphtha cracking process consumes more than 30 % of the total amount of energy required in petrochemical production, so more efficient processes for the production of light olefins are highly desirable. Moreover, the relative demand for propylene has increased due to the large-scale production of ethylene in the Middle East and China. Catalytic cracking of naphtha over solid-acid catalysts can provide a high propylene/ethylene ratio at low reaction temperatures compared with thermal cracking6), so use of this process could provide energy savings together with the selective production of propylene. Accordingly, the catalytic cracking of naphtha is expected to be an effective alternative to the thermal cracking process. Promising catalysts for n-hexane cracking include the zeolites, which are crystalline aluminosilicate materials with various properties, such as strong acidity and high surface area, and catalytic cracking of alkane over zeolite catalysts has been investigated7)~9). Zeolites incorporate intracrystalline micropores and nanospaces close to the molecular diameters of light hydrocarbons, so have remarkable molecular-sieving effects for light hydrocarbons and have been widely used as shapeselective catalysts in various hydrocarbon processes, such as the alkylation of aromatics10),11) and synthesis of olefins from alcohol and acetone12),13). However, the crystal sizes of zeolites are usually much larger than the sizes of the micropores, so the rate-limiting step of the reaction tends to be diffusion of the reactant/product molecules within the micropores. Moreover, carbon solid (coke) readily forms near the external surface of the crystal under diffusion-controlled conditions, resulting in rapid blocking of the pores, leading to a short catalyst lifetime. Nano-sized zeolites are effective to achieve low diffusion resistance, because the diffusion length for reactant/product hydrocarbons, which depends on the zeolite crystal size, is reduced. We have successfully prepared MFI-type and MORtype zeolite nanocrystals via hydrothermal synthesis in a water/surfactant/organic solvent (emulsion method)14)~18). The nano-sized zeolites are expected to be effective catalysts with low diffusion resistance as well as large external surface area, which will improve the catalytic activity and lifetime. In the present study, catalytic cracking of n-hexane, as a model reaction for the catalytic cracking of naphtha, was examined over MFI-type zeolites, and the effects of the Si/Al ratio and 267 Journal of the Japan Petroleum Institute, 55, (4), 267-274 (2012)

Numerical simulation of the thermal-gradient chemical vapor infiltration process for production of fiber-reinforced ceramic composite

Abstract A numerical model was developed in order to describe the thermal-gradient chemical vapor infiltration (CVI) for the production of SiC W /Al 2 O 3 composite. The proposed model considered reaction, diffusion and deposition of alumina within the porous preform. The cubic array of disconnected cylinders model was proposed in order to represent the porous structure of the preform and the composite. The experimental results of CVI were in good agreement with the calculated results. The effects of total pressure, heating temperature and initial surface temperature on the final residual porosity and the infiltration time were investigated. The heating temperature and the initial surface temperature had a larger effect on the porosity and the infiltration time than did the total pressure. In order to produce a dense composite, the initial surface temperature must decrease with increasing heating temperature.

Preparation of size-controlled Pt catalysts supported on alumina

It was found that Pt particles on Al2O3-supported Pt catalysts prepared using Pt complex nanoparticles formed in a water-in-oil microemulsion became very small and uniform compared to those prepared using reduced Pt metal nanoparticles or by an impregnation method. Moreover, the catalytic activity of the catalyst composed of very small Pt particles, which was prepared using the complex nanoparticles, was higher in the NO–CO reaction than those of the other catalysts.

Chemical vapor infiltration and deposition to produce a silicon carbide-carbon functionally gradient material

Functionally gradient material (FGM) that had a layer in which the chemical composition changed gradually from C to SiC between the C/C composite and the surface SiC layer was prepared. The 3D-woven carbon fiber preform was solidified partially by liquid-phase impregnation with a resol-type cresol resin. The preform was further solidified by thermal-gradient chemical vapor infiltration of carbon from propane. A consistent compositionally gradient protective layer was prepared by chemical vapor deposition by changing the reactant mixture composition gradually from propane to dimethyldichlorosilane. Thus an FGM with a continuous composition distribution was obtained. No thermal cracks were observed and the compositionally gradient layer remained adhesive to the base composite following repeated rapid cooling tests from 1000 to 0°C.