Effects of support and additive on oxidation state and activity of Pt catalyst in propane combustion

The effects of support and additive on the oxidation state and catalytic activity of Pt catalyst in the low temperature propane combustion were systematically investigated on Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂–Al₂O₃. The catalytic activity varied much with both support materials and additives. The catalyst on the more acidic support showed higher activity, and the catalytic activity on every support materials increased as the electronegativity of additives increased, while some additives decreased the activity. The oxidation state of platinum, estimated by white line intensity of Pt L_III-edge XANES spectrum, also varied with the support and additives, and additives with higher electronegativity greatly prevented the platinum from its oxidation under oxidising atmosphere. Among almost all the catalysts with various supports and various additives, a clear relationship was observed between the oxidation state of platinum and the catalytic activity; the more metallic platinum showed higher activity. Thus, it was concluded that the total electrophilic/electrophobic property derived from those of the support and additive controls the oxidation state of platinum, which intensively affects the catalytic activity; i.e. higher electrophilic property provides less oxidised platinum, resulting in high catalytic activity. The mechanism of this effect was also discussed on the basis of thermochemical data, and it was proposed that the electrophobic materials promote the noble metal oxidation since the noble metal oxo-anion such as PtO^δ− is more stabilised with electrophobic cation.     

Synthesis of poly(α-thiophenediyl)benzylidene with high molecular weight and its thermal stability

Summary The synthesis of poly(-thiophenediyl)benzylidene (PTB) with high molecular weight is described. Number-average degrees of polymerization reached about 74. The characterizations of the polymer was investigated by ¹H-NMR, ¹³C-NMR, IR, and UV-VIS spectra. The polymer with well-defined structure and high molecular weight was obtained by polymerization at low temperature and in polar solvent. This polymer was thermally stable and a thermal decomposition took place at 391°C under nitrogen and at 370°C under air. The glass transformation temperature was 117°C and this PTB was nonfusible.     

Surface active N-acylglutamate: I. Preparation of long chain N-acylglutamic acid

Long chain N-acylglutamic acid was prepared in a high yield by a reaction of glutamic acid with fatty acid chloride in a mixed solvent of water and a water miscible organic solvent such as acetone, methyl ethyl ketone, dioxane, tetrahydrofuran,t-butyl alcohol or cyclohexanone. In this reaction the composition of the mixed solvent influenced the yield of N-acylated glutamic acid and the best yield was obtained when the reaction was carried out in the mixed solvent comprising 30–60% v/v of the organic solvent. Long chain N-acylaspartic acid was also obtained in a high yield by the same method. As the other method to obtain N-lauroyl-D L-glutamic acid, it was examined that N-acyl-α-aminoglutarodinitrile which was obtained by a reaction of α-aminoglutarodinitrile with fatty acid chloride was hydrolyzed with an aqueous alkaline solution. The salts of long chain N-acylglutamic acid are known as the surface active agents that react mildly on the human skin.     

PbTiO3–PbO–SiO2 Glass-Ceramic Thin Film by a Sol–Gel Process

PbTiO₃(PT)-PbO-SiO₂ glass-ceramic thin films were pro-duced by a sol-gel process. The crystallization of PT oc-curred at ∼700°C and was higher than that in PT-PbO-B₂ O₃ sol-gel glass-ceramics. A pinhole-free thin film was obtained by a rapid thermal annealing process when the designed glass-forming phase content in the thin film was >24 vol%. The measured dielectric constants of the films fairly agreed with the predicted values, based on a parallel mixing model. The dielectric constant was 219 and the di-electric loss was 0.04 in the 0.6PT-0.4(PbO-SiO₂) film that was fired at 700°C.     

New amphoteric surfactants containing a phosphoric acid group: I. syntheses and physicochemical properties of sodium 2-(n-2-hydroxyalkyl-n-methylamino)ethyl hydrogen phosphate

A series of new amphoteric surfactants having a phosphoric acid group, a tertiary amino group and a 2-hydroxyalkyl group, sodium 2-(N-2-hydroxyalkyl-N-methyl-amino)ethyl hydrogen phosphates (alkyl: n-tetradecyl, n-hexadecyl, n-octadecyl), were prepared by an addition reaction of 1,2-epoxyalkanes to N-methylaminoethanol, followed by the introduction of a phosphoric acid group and neutralization with sodium hydroxide. The structures of these compounds were confirmed by spectroscopy and elemental analysis. The solubility in solvents, Krafft point, surface tension, critical micelle concentration (CMC), occupation area of the molecule at the surface of aqueous solutions and foaming power were measured. It was shown that a 2-hydroxyethyl group in a long alkyl chain seemed to behave as a hydrophobic part.     

The degradation of polystyrene during extrusion

An investigation was made of the magnitude and mechanism of shear degradation of a narrow distribution, high molecular weight (M_w = 670,000) polystyrene. An Instron rheometer was used to perform the extrusion at temperatures from 164° to 250°C. The change in molecular weight distribution was studied by gel permeation chromatography. The maximum shear stress employed was 5.83 kg/cm². It was found that degradation could be induced at high stress at temperatures of 50°C lower than degradation of polystyrene would occur exclusively due to thermal forces. An activation energy for the degradation, calculated at constant shear rate, was +20.2 kcal/mole. The direction and magnitude of this value are consistent with degradation induced through a mechanical reduced activation for thermal degradation.     

Characterization of highly active silver catalyst for NOx reduction in lean-burning engine exhaust

A new Ag/Al₂O₃ catalyst for removing NOx in lean exhaust gas was developed. Oxidized Ag/Al₂O₃ catalyst is highly active for reduction of NOx with ethanol and propene, whereas reduced Ag/Al₂O₃ catalyst is less active for these reactions. Selectivity to N₂ is also high on the oxidized Ag/Al₂O₃ compared to that on the reduced Ag/Al₂O₃. XRD and SEM studies of these two types of Ag catalysts suggest that oxidation induces an interaction between Ag and the support, where the particles are grown in large size. In contrast, the metallic Ag particles are finely dispersed by the reduction process. Although dispersion of Ag particles is decreased by the oxidation process, the catalytic activity is increased. This suggests that the Ag-alumina sites created in the high temperature oxidizing environment are active in catalytic reduction of NOx. This revised version was published online in July 2006 with corrections to the Cover Date.     

1-O-alkyl-2,3-diacylglycerols in the skin surface lipids of the hairless mouse

A neutral lipid class was isolated by thin-layer chromatography from the skin surface lipids of the hairless mouse. The fraction migrated faster than triglycerides and had a migration rate similar to that of diacyl alkanediols (diester wax). Upon deacylation, however, the long-chain diols were identified as 1-alkylglycerol ethers based on their chromatographic properties and on the mass spectra of their nicotinylidene derivatives. Thus, the skin lipid fraction was identified as 1-O-alkyl-diacylglycerol. The alkyl moieties were all saturated and even-numbered and ranged in chainlength from C₁₆ to C₂₂ with 1-O-hexadecylglycerol amounting to 34% of the total glycerol ether moieties. The fatty acids derived from this lipid fraction were mostly monoenoic with chainlengths ranging from C₁₆ to C₂₄. The major acyl component was eicosenoic acid (20∶1) representing 61% of the total fatty acids.     

Polymerization of 2-dibutylamino-1,3,5-triazine-4,6-dithiol on wire during friction process

2-Dibutylamino-1,3,5-triazine-4,6-dithiol (DB) and a mixture of DB and triallylisocyanurate (TAIC) were used as a lubricant during steel wire drawing due to a dry process. DB gave a polymer film with 180 nm in thickness to wire surfaces during the wire drawing. The polymer film had a disulfide structure on the backbone and contained a small amount of DB monomer and olygomer. Molecular weight and polymer weight increased with the drawing rate. The mixture of DB and TAIC gave mainly a three-dimensional polymer film with 225 nm in thickness to wire surfaces during drawing. The polymer film insoluble in THF had mono and disulfide structures and contained a small amount of linear polymer, DB, and TAIC. Such tribological polymerizations are estimated as follows: DB produces dithiyl radicals on a nascent surface formed during drawing and in the presence of oxygen and heat. The dithiyl radicals were polymerized by coupling with each other to give disulfide bonds or added to allyl groups in TAIC to give monosulfide bonds. It is concluded that this technique should be possible to use for unifying metal processing and surface treatment. © 1995 John Wiley & Sons, Inc.