Role of tungsten in promoting selective reduction of NO with CO over Ir/WO3–SiO2 catalysts

Catalytic hydrogenation of naphthalene to decalin was studied over a carbon-supported rhodium catalyst in supercritical carbon dioxide solvent at 333 K, and the results were compared with those in an organic solvent. cis-, trans-Decalin and tetralin were formed from the beginning of the reaction in supercritical carbon dioxide. Higher concentration of hydrogen in carbon dioxide solvent and on the active site, and also the suppression of desorption of partially hydrogenated tetralin molecules from the active site would be responsible for higher selectivity to cis-decalin in supercritical carbon dioxide than that in an organic solvent.     

Catalysis of gasification of coal-derived cokes and chars

Calcium is the most important in-situ catalyst for gasification of US coal chars in O₂, CO₂ and H₂O. It is a poor catalyst for gasification of chars by H₂. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O₂, CO₂ and H₂O. Carbon monoxide inhibits catalysis of the CH₂O reaction by calcium, potassium and sodium; H₂ inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH₂O reaction. Iron is not an important catalyst for the gasification of chars in O₂, CO₂ and H₂O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H₂ + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H₂O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron.     

Some theoretical aspects of the electrophoretic sedimentation of particles

This paper concerns the theoretical interpretation of the results of a previous experimental study of the sedimentation of oxidized fine aluminum and iron particles in waste kerosene under the influence of an electric field. Following the Kynch analysis of the mode of gravity sedimentation, a modified particle volume flux is introduced to compensate for the effect of the electric field strength. It is shown that if the local electric field strength at the settling interface is used as the true driving force for electrophoretic sedimentation, the settling curves can be predicted with reasonable accuracy, provided that electrical heating effects and consequent temperature changes in the system are taken into account.Some theoretical aspects of the effects of dielectric polarization on settling are also discussed and illustrated qualitatively by the experimental data. Finally, some of the factors which might be expected to affect the energy efficiency of a particle separator operating by electrophoretic sedimentation are considered.     

Preparation of modified poly(vinyl chloride) containing N,N-di(β-hydroxyethyl)dithiocarbamate and its reaction with metal ions

Reaction of N,N-di(β-hydroxyethyl)dithiocarbamate ion with poly(vinyl chloride) (PVC) was undertaken, and the reaction with metal ions of the polymer obtained was investigated. The effect of γ-irradiation on the reaction with metal ion was also studied. The modified PVC (PHDC) obtained from the reaction with N,N-di(β-hydroxyethyl)dithiocarbamate ion is pale yellow even after reaction at 100°C for 5 hr in dimethylformamide (DMF); it is soluble in dipolar solvents and its chlorine content is decreased considerably. This polymer reacted well with acetate salts of copper(II), nickel(II), zinc(II), and silver(I) heterogeneously in aqueous solution because of the introduction of hydrophilic groups (two hydroxy groups). The reactivity of the metal ions toward the polymer was of the order Ag(I) ? Cu(II) > Ni(II) > Zn(II). From the result of the reaction of γ-irradiated polymer with cupric ion, the polymer was judged to have fairly good antiradiation property.     

Efficient usage of highly dispersed Pt on carbon nanotubes for electrode catalysts of polymer electrolyte fuel cells

A Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in polymer electrolyte fuel cells (PEFCs) below 500 mA/cm². K₂PtCl₄ and H₂PtCl₆·6(H₂O) are used for the Pt deposition onto multi-walled CNTs (MWCNTs), which are produced by the catalytic decomposition of hydrocarbons. The electric power densities produced using the Pt/CNT electrodes are greater than that of the Pt/CB by a factor of two to four on the basis of the Pt load per power. CNTs are thus found to be a good support of Pt particles for PEFC electrodes. TEM images show 2–4-nm Pt nanoparticles dispersed on the CNT surfaces. These high performances are considered to be due to the efficient formation of the triple-phase boundaries of gas–electrode–electrolyte. The mechanisms of Pt deposition are discussed for these Pt-deposited CNTs.     

Study on modified phenolic resin. II. Modification with p-hydroxyphenylmaleimide/styrene copolymer

The improvement of heat resistance and mechanical properties of phenolic resin was examined with the blend of novolac and copolymers prepared from p-hydroxyphenylmaleimide (HPMI) and styrene. Copolymers of HPMI and styrene with various molecular weights were synthesized. Glass transition (T_g) and thermal decomposition temperatures of the copolymers were measured by differential scanning calorimetry (DSC) and thermogravimetry (TG), respectively. The miscibility of the copolymers with novolac was examined by DSC. It was found that the copolymers had a good heat resistance and a good miscibility with novolac. Molding compounds were prepared by hot roll-kneading of mixtures that involved novolac, copolymer, hexamethylenetetramine (hexamine), and glass fiber. It was found that the test pieces prepared by transfer molding from the molding compounds showed a good heat resistance and better mechanical properties than phenolic resin modified with HPMI homopolymer.     

Effect of polymer density on polyethylene hollow fiber membrane formation via thermally induced phase separation

Microporous high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) hollow fiber membranes were prepared from polyethylene–diisodecyl phthalate solution via thermally induced phase separation. Effect of the polyethylene density on the membrane structure and performance was investigated. The HDPE membrane showed about five times higher water permeability than the LDPE membrane because it had the larger pore and the higher porosity at the outer membrane surface. The formation of the larger pore was owing to both the initial larger structure formed by spinodal decomposition and the suppression of the diluent evaporation from the outer membrane surface due to the higher solution viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 471–474, 2004     

Studies on phase separation rate in porous polyimide membrane formation by immersion precipitation

Phase separation rate during porous membrane formation by immersion precipitation was investigated by light scattering in a polyimide/N‐Methylpyrrolidone (NMP)/water system. In the light scattering measurement, plots of scattered intensity against scattered angle showed maxima in all cases, which indicated that phase separation occurred by a spinodal decomposition (SD). Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient D_app and an interphase periodic distance Λ, were obtained. The growth process of Λ was also followed by light scattering. The growth rate had the same tendency as D_app when water content in the nonsolvent bath and the polymer concentration in the cast solution were changed. The pore size of the final membrane increased with decreasing water content, which was opposite to the tendency of Λ growth rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 292–296, 2003     

Silica-supported cobalt catalysts for the selective reduction of nitrogen monoxide with propene

Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO₂ prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co²⁺ ions on silica are responsible for the catalytic activity.     

Sterols ofKalanchoe pinnata: First report of the isolation of both C-24 epimers of 24-alkyl-Δ25-sterols from a higher plant

Eighteen sterols were isolated from the aerial parts ofKalanchoe pinnata (Crassulaceae) including four novel sterols,viz. (24R)-stigmasta-5,25-dien-3β-ol (24-epiclerosterol), (24R)-5α-stigmasta-7,25-dien-3β-ol, 5α-stigmast-24-en-3β-ol, and 25-methyl-5α-ergost-24(28)-en-3β-ol. 24-Epiclerosterol and its Δ⁷-analog occur together with their 24S/β-epimers in the same plant making this the first report of the isolation of both C-24 epimers of Δ²⁵-unsaturated 24-alkylsterols from a non-marine organism. Iodine-catalyzed isomerization of stigmasta-5,24-dien-3β-ol (24-ethyldesmosterol), the main sterol ofK. pinnata, yielded 24-epiclerosterol among other products.