Yasunori Kuriki

Dispersion of metal nanoparticles for aligned carbon nanotube arrays

We report that Co metal nanoparticles (an average diameter of 4 nm) chemically synthesized by a reverse micelle method catalyzes the growth of multiwall carbon nanotubes (MWNTs) aligned perpendicular to a substrate. The surface of the nanoparticles is covered with surfactants so that the nanoparticles can be dispersed in organic solvent. The dispersion of the nanoparticles was cast directly onto a plane Si substrate for thermal pyrolysis of acetylene. We have found that the pretreatment of the metal nanoparticles with hydrogen sulfide before the pyrolysis straightens the MWNTs, suggesting sulfurization of the nanoparticle catalyst plays an important role in regular growth of the MWNTs. The dispersion of the nanoparticles offers a conventional and processible approach to synthesize large area aligned MWNT arrays.

Geometrical structure and electronic properties of atomically resolved multiwall carbon nanotubes

Multiwall carbon nanotubes (MWNTs) are predicated to exhibit various electronic properties depending on their diameters and chiralities. The existence of multishells offers the possibility of switching between high and low conducting states within the same nanotube. So far, it has been a big challenge to probe the structure and the electronic properties of different MWNT shells. Here we report the nanostructure measurements of MWNT together with their electronic properties as revealed by a scanning tunneling microscope. The images show tubes with different chiralities (0°–30°) and diameters (4–9 nm). Upon thermal oxidation in air, we have observed diameter-dependent tube opening. MWNTs with large diameters (7–9 nm) show open ends while smaller diameters have closed ends. The structure of open end shows unsaturated bonds, which offers rich chemistry to develop molecular technology based on carbon nanotubes. Finally, we present the structure of the inner shells of MWNT.

Angular-resolved EELS of a carbon nanotube

Abstract Electron energy loss spectroscopy (EELS) and electron spectroscopic imaging techniques are applied to a carbon nanotube (NT) to reveal the fine electronic state in the cylindrical structure of graphite. Although NTs with large diameters show similar EELS patterns at the carbon K-edge (285 eV) to those of graphite, a fine molecular straw with a diameter less than 5 nm exhibits different features. Especially it was found that the angular-resolved EELS formed by electrons scattered normal to the longitudinal axis of the NT indicates a strong contribution of π∗ excitation compared with σ∗ excitation. It confirms that the anisotropy of the NT exists in the structure and electronic structure.

Structural identifications of straight-chain fatty acids and esters in coal extracts by linked scanning mass spectrometry

Abstract Structural identifications of geochemically significant straight-chain fatty acids and esters in coal extracts were carried out by linked scanning mass spectrometry together with field desorption mass spectrometry. The results obtained demonstrate the usefulness of the technique for direct analysis of complex mixtures to elucidate detailed molecular structures of individual constituents. The extracts of lignites contain straight-chain fatty acids with C 24 to C 34 and long-chain fatty esters with C 48 to C 64 , the latter being missing from subbituminous coals and neither is found in those of bituminous coals. The free fatty acids, the acyl and the alkoxyl groups of esters all extend from C 24 to C 34 and are qualitatively similar to each other in carbon-number distribution indicating that they were probably derived from common precursor compounds. The presence and/or absence of fatty acids and fatty esters parallels the rank of coals and may be connected with chemical changes brought about during maturation, such as hydrolysis of the esters, conversions of the acids into paraffins, etc.

C K-edge X-ray absorption near-edge structure of carbon nanotubes

C K-edge X-ray absorption near-edge structure of the carbon nanotubes was measured by monitoring the total electron yield from the sample. The spectrum shows similar features to those of graphite except the feature between the lowest anti-bonding π and σ bands called the interlayer band.

Mechanical milling of metal sulfide particles and their catalytic activity—hydrogenation of 1-methylnaphthalene with molybdenum sulfide

Abstract The comminution of molybdenum sulfide particles with a vibrating mill and with a media-agitating mill was investigated. For equivalent milling times, the media-agitating mill prepared smaller molybdenum sulfide particles than the vibrating mill. Median particle diameters were approximately 40 nm for molybdenum sulfide particles comminuted for 50 h with the media-agitating mill. The specific surface area of these particles was about 120 m2/g. In comparison, the surface area of the starting material was 5.8 m2/g. The layered structure of molybdenum sulfide was sustained after the milling, although the crystal stacking height relative to the edge surface area decreased. Catalytic activities of the raw and comminuted molybdenum sulfide were measured using the hydrogenation of 1-methylnaphthalene as a model reaction. The hydrogenation rate constants per weight of comminuted catalyst were much higher than those of the raw material and increased with the specific surface area. Conversely, the rate constants per surface area were almost the same irrespective of both the comminution time and the comminution method. The increased catalytic activity is believed to be caused by a change in crystal structure and morphology.

Synthesis and Catalytic Activity of Ultra Fine Metal Sulfide Particles

Publisher Summary This chapter discusses ultra fine metal sulfide particles, which are synthesized by two different methods and the catalytic activity of the metal sulfide particles. The activation of metal surface molybdenum, cobalt, nickel, and iron (Mo, Co, Ni, Fe) by mechanical vibration is quite small. Fine particles of metal sulfide are produced by this method. Hydrogenation activity of these ultra fine metal particles per weight is as follows: Co > Ni > Fe. The structure of sulfided Co was Co 9 S 8 , but that of sulfided Ni is a mixture of Ni x S y (x>y). The synergy effect of Fe and Co in case of alloy of Fe and Co is not found. These catalysts are now applied for the liquefaction of wandoan coal.

Effects of Catalyst Concentration and Gas-liquid Mass Transfer on Coal Liquefaction.

To evaluate the effects of catalyst concentration on liquefaction, concentration distributions of the catalyst particles in a slurry reactor were estimated and autoclave experiments were carried out under various gasliquid mass transfer conditions.The estimation showed following results. The concentration distributions of catalyst particles became more uniform with smaller iron particles. And when dp<dpap=min, ap (surface area of catalyst particles in a slurry) increased with decreasing dp (diameter of catalyst particle).The autoclave experiments showed following results. Coal conversions increased with increasing of catalyst concentration under the good mass tranpfer condition. On the other hand, under the poor mass transfer condition, the conversions decrease at high catalyst concentration.The results which used hydrogenated anthracene oil as a solvent showed higher oil yields with lower hydrogen consumption. Yields of methane under the poor mass transfer condition were higher than those of under the good mass transfer condition, it shows that production of methan reflect the mass transfer condition in the reactor.These results suggest that using of smaller iron particle catalyst and better donor solvent under the condition of better gasliquid mass transfer lead to higher coal conversion.

Synthesis of Ultra Fine Metal-Carbon Composite Particles by Carbon Arc-Plasma and its Catalytic Activity.

Ultra fine particles of Fe, Ni, Co and Mo with diameter of 5-20 nm were synthesized. The particles were stable under the atmosphere because they were surrounded with graphite sheet and amorphous carbon. Catalytic activities of them for hydrogenation of 1-methyl naphthalene were tested. It was found that ultra-fine particles of Ni-carbon composite had high catalytic activities. The kinetic analysis shows that more active hydrogenation catalysts can be prepared by bi-metallic clusters.

Effect of type of Mo catalyst on coal liquefaction

Publisher Summary This chapter discusses the effect of the Mo catalyst on coal liquefaction. Dispersion of Mo metal in the solvent is important to improve catalyst performance using anthrathene oil (AO) solvent. Contact of Mo metal and solvent is essential in the liquefaction reaction. By comparing the results of AO and hydrogenated oil (HAO), the gas-phase hydrogen is transferred to the coal mainly through solvent. The effect of the Mo catalyst on the coal liquefaction is experimented on the coal liquefaction using different types of Mo catalyst. Oil soluble Mo is used in two different types: dissolving in the solvent and impregnating in the coal.