Takanori Mizushima

Thermal and chemical recycle of waste polymers

Abstract Catalytic degradations of polyethylene into fuel oils and of polystyrene into styrene monomer have been studied using solid acids and bases as catalysts. Solid acids such as silica-aluminas and ZSM-5 zeolite were found to be effective to degrade waste polyethylene into fuel oils, and solid bases such as BaO and K 2 O were concluded to be effective to convert waste polystyrene into styrene monomer. A design of recyclable polystyrene films will be briefly mentioned.

Oxygen storage capacity (OSC) of aged Pt/CeO2/Al2O3 catalysts : roles of Pt and CeO2 supported on Al2O3

Abstract In order to investigate the behavior of Pt and CeO2 on the Pt/CeO2/Al2O3 catalyst after aging at 1273 K, the oxygen storage capacity(OSC) has been measured and physically mixed catalysts such as Pt Al 2 O 3 + CeO 2 Al 2 O 3 , Pt Al 2 O 3 + CeO 2 , Pt CeO 2 + Al 2 O 3 and Pt CeO 2 + Pt Al 2 O 3 catalysts have been employed for comparison. After the aging, the OSC of the physically mixed catalysts whose CeO2 was not supported on Al2O3 became poor because of the large-sized CeO2 and the deactivation of Pt, although those catalysts provided large OSC assisted by the PtCeO2 interaction before the aging. The OSC increment calculated by subtraction of the OSC of Pt Al 2 O 3 + CeO 2 Al 2 O 3 from that of Pt/CeO2/Al2O3 indicated that both the PtCeO2 interaction and the dispersed CeO2 on Al2O3 are essential for the generation of OSC, even after the aging.

Hyperstoichiometric hydrogen occlusion by palladium nanoparticles included in NaY zeolite

Abstract Amounts of occluded hydrogen in palladium-containing NaY zeolites increased with the palladium content. Allocation of mols of hydrogen atoms to palladium gave large H/Pd ratios higher than unity at 298 K under 100 kPa of hydrogen. As the palladium content increased, the proportion of the external palladium increased and the H/Pd value decreased to approach that for powdery palladium. The hyperstoichiometric occlusion of hydrogen can be attributed to palladium nanoparticles or clusters inside the pores of zeolite. Whereas the interstitial site per palladium atom was unity for powdery palladium, for the internal palladium species it seemed to be two or more. Before reaching the stoichiometric composition, PdH, the palladium species released substantial heat on hydriding similarly to powdery palladium. After the hydrogen content exceeded the stoichiometry, the heat on hydriding was as low as 1 kJ/mol H 2 .

Preparation of niobium oxide films as a humidity sensor

Abstract Niobium oxide films were prepared over a quartz plate by withdrawing it from a solution of niobium penta-isopropoxide (NIP) dissolved in sec-propyl alcohol. The films calcined at 673 K were well controlled in the film thickness either by NIP concentration in the solution or by the withdrawing rate of the quartz plate from the solution. BET surface area of the calcined films was as huge as around 400 m2g−1 and was not reduced by cyclic adsorption/desorption of water vapor. A rapid decrease and increase in the electrical resistivity of the calcined films was well associated with the cyclic adsorption/desorption of water vapor. The decrease in the electrical resistivity of the films by water vapor adsorption was more than 10 times sensitive than the decrease caused by the adsorption of ethanol, hydrocarbons, carbon monoxide and carbon dioxide. These results suggest an application of the niobium oxide films as an element of a humidity sensor. The calcined films were proved by SEM observation to consist of tiny particles possessing a lotofmicropores sized less than 20 A. The decrease in the electrical resistivity of the films, or the increase in the electrical conductivity, was attributed to the water vapor adsorbed in these micropores. In order to identify the charge carriers during water vapor adsorption on the films, changes in the impedance and the phase shift caused by water vapor adsorption were measured using an LCR meter in AC frequency range of 10 Hz to 100 kHz. From a complex impedance plotting, single semicircule was obtained for water vapor adsorption onto the films, suggesting single adsorbed species as a charge carrier. Assuming an equivalent electric circuit for the films adsorbing water vapor, a constant capacitance was calculated under various partial pressures of water vapor, probably suggesting that the charge carriers will be H3O+ on the films.

Characterization of silica-supported bimetallic iron-nickel catalysts by EXAFS

FeNi/SiO2 bimetallic catalysts with varying composition were prepared according to two procedures: alkoxide and impregnation methods. The size distribution of the metal clusters and the local structure around each kind of metal atom in the clusters are studied by TEM, XRD, and EXAFS. Fe and Ni atoms are concluded to be in small clusters with a fcc structure; that is, alloy is formed. The metal particles are not, however, uniform in composition and consist of an Ni-rich kernel covered with outer layers which contain more Fe. This tendency is more pronounced in the catalyst prepared by the alkoxide method. The reason for the evolution of such inhomogeneous clusters is examined by EXAFS through the local structure change during the preparation procedure.

Behaviour of oxygen species adsorbed on Al2O3-supported cerium oxide catalysts for methane oxidation

The properties and catalytic behaviour of adsorbed oxygen species on alumina-supported cerium oxides (CeO2, CeAlO3 and CeO2 –x) for methane oxidation have been investigated by means of EPR, FTIR, temperature-programmed desorption (TPD) and 18O tracer techniques. The adsorbed oxygen on the cerium oxide catalysts was found to be the side-on type O2– ion by EPR and FTIR measurements. The adsorption site of the O2– ion on CeO2 –x/Al2O3 was assumed to be the site formed by the ensemble effect between oxygen vacancies and surface cations, while on the other catalysts the sites were cerium ions on the surface. The oxygen species desorbed after 18O2 adsorption at 773 K were 16O2 and 16O 18O in all catalysts, and the major products for methane oxidation were C16O2 and C16O 18O. These suggest that the adsorbed oxygen is activated through the lattice in cerium oxides. The activities of methane oxidation were influenced by the oxygen diffusion processes on the cerium oxides.

Enhancement of Fluorescent Intensity of a SiO2 : Sm Glass by Al Codoping and Local Structure around Sm by an EXAFS Study

An addition of Al ions is found to increase emission intensity form Sm ion more than an order of magnitude. EXAFS study revealed that local structures around Sm ions in the phosphors with and without dopant are significantly different; in the SiO 2 : Sm phosphor Sm atoms are well dispersed at low Sm concentrations and Sm atoms agglomerate at high concentrations, while in the Al codoped phosphor Sm atoms are coordinated by Al through Sm-O-Al bonding. This provides a direct structural evidence of the role of the codopant

Laboratory EXAFS by Fluorescence Detection

It is demonstrated that a slight modification of a laboratory EXAFS (extended X-ray absorption fine structure) spectrometer for fluorescence detection can greatly lower the limit of dilution. It can also extend samples studied to thin films on X-ray opaque substrates. Basically the system consists of a laboratory EXAFS spectrometer eguipped with two NaI scintillation counters combined with filters, and an SSD (solid state detector). Optimum experimental conditions are chosen by monitoring the output of the SSD, and then scintillation counters are used for measurements by making use of the large aperture. The performance of this system was tested by dilute aqueous solutions of Fe(NO3)3, 1000 and 5000 A thick iron film deposited on glass substrates, a 6 mM solution of octaethylporphyrin iron (III) chloride (Fe(OEP)Cl).

Selective preparation of β-MoO3 and silicomolybdic acid(SMA) on MCM-41 from molybdic acid precursor and their partial oxidation performances

Abstract SMA(Mo/MCM-41Imp) and β-MoO 3 (Mo/MCM-41 Evap) were successfully prepared on MCM-41 using the molybdic acid solution. The molybdic acid solution is the effective precursor to generate selectively either SMA or β-MoO 3, and those species are anchored on MCM-41 through the formation of SMA. The Mo/MCM-41Imp catalyst showed a good catalytic performance for partial oxidation of methane to formaldehyde while the Mo/MCM-41 Evap is a promising catalyst for partial oxidation of methanol to formaldehyde.

NICKEL INCORPORATED INTO ANODIC POROUS ALUMINA FORMED ON AN ALUMINIUM WIRE

Porous alumina films have been prepared on the surface of an aluminium wire by anodic oxidation in an oxalic acid electrolyte. The pore size could be controlled by the anode potential, and the thickness of the alumina film was a function of the anodizing time as well as the anode potential used. Silica powders containing finely divided Ni metal particles were incorporated into the micropores of the alumina films, which were then used as wire catalysts. The wire catalyst did not require any supplementary heating during catalytic reactions, since after 1 min of applying a small voltage across the ends of the wire, a temperature of 573 K could be reached. The catalytic performance of the nickel particles mounted in the aluminium wires for the hydrogenation of but-1-ene was measured and compared with that of a conventional supported-nickel catalyst.