Showing papers by "National Chemical Laboratory published in 1990"

Selective reduction of nitrogen oxides with hydrocarbons over solid acid catalysts in oxygen-rich atmospheres

Abstract: Highly selective reduction of nitrogen oxides to dinitrogen occurs to a high level in oxygen-rich atmospheres by using a small amount of propane as a reducing agent over alumina, silica-alumina, titania and zirconia catalyst. Judging from the data of activity and ammonia TPD measurement on a series of silica-alumina catalysts, acidity is suggested to be one of the main factors that determine catalytic activity.

Characteristics of Slurry‐Coated Nickel Zirconia Cermet Anodes for Solid Oxide Fuel Cells

Abstract: Polarization characteristics were studied in nickel and yttria stabilized zirconia cermet (Ni-YSZ cermet) electrodes in order to search for an adequate fabrication condition of a planar solid oxide fuel cell. Several electrodes were prepared by the slurry coating method, and dc and ac polarization behaviors were investigated at 1273 K in H 2 -H 2 O atmosphere. An experimental equation was derived to describe a typical dc polarization curve of a Ni-YSZ cermet electrode. Effects of fabrication temperature, nickel content, and material powder were investigated in terms of deviation from this equation. Anodic overvoltage with a carefully prepared electrode was decreased to about 0.12 V at 1 A/cm 2

Precocious flowering and seeding behaviour in tissue-cultured bamboos

Abstract: BAMBOO flowers only once during its lifetime, dying at the end of its first fruiting season. This monocarpic flowering is intriguing not only in that it occurs after a lapse of 12 to 120 years, but because it is 'gregarious', local populations of bamboo flowering together and then dying. New bamboo plants are produced either by vegetative subdivision or from seed. Breeding of bamboo, however, has proved to be extremely difficult: seed production depends on unpredictable circumstances and events1, and the basis of gregarious flowering, and the causes of death and flowering, are not known. Flowering in vitro has previously been studied by culturing expiants of stem tips, mature stems, roots, petioles, leaves, inflorescences, flowers and so on2–5. Although bamboo plantlets have been formed by means of organogenesis and embry-ogenesis6–8, in vitro flowering has not previously been reported for bamboo. We now report on an in vitro system in which we could consistently induce flowering in the two species of bamboo Bambusa arundinacea Willd and Dendrocalamus brandisii Kurz. Inflorescence expiants containing a panicle of spikelets gave rise to several viable inflorescences on subculture; fertile seeds were also produced. Further refinements to this system could lead to the introduction of breeding programmes to improve bamboo, and to the production of perennial seeds for bamboo, as well as to a better understanding of the physiology underlying flowering behaviour in bamboo.

Sinterability and electrical conductivity of calcium-doped lanthanum chromites

Abstract: Calcium-doped lanthanum chromites, (La1−xCax) (Cr1−y Cay O3, have been synthesized to investigate effects of calcium doping on sinterability and electrical conductivity. X-ray diffractometric results have revealed that in addition to normal perovskites (La1−xCaxCrO3), chromium-deficient perovskites can exist as a single phase in the composition region 0.1

Photocatalytic degradation of organochlorine compounds in suspended TiO2

Abstract: Twelve organochlorine solvents which are di-, tri- and tetrachloro derivatives of methane, ethane and ethylene, were photocatalytically degraded on TiO 2 , platinum (Pt)-loaded TiO 2 and TiO 2 with added H 2 O 2 . It was found that for derivatives of the three compounds the degradation rates were in the order Cl 2 > Cl 3 > Cl 4 , and for those containing the same number of Cl substituents the order was ethylene > ethane. During the degradation of each organochlorine solvent, Cl − was liberated simultaneously. On Pt-loaded TiO 2 , Cl − was transformed into ClO 3 − photocatalytically. Stoichiometry for the photocatalytic degradation of dichloroethylene was C 2 H 2 Cl 2 + 2O 2 → 2Cl − + 2CO 2 + 2H + .

XANES and EXAFS analysis of copper ion-exchanged ZSM-5 zeolite catalyst used for nitrogen monoxide decomposition

Abstract: XANES and EXAFS analysis of Cu ion-exchanged ZSM-5 zeolite, a highly active catalyst for NO decomposition, is performed. The copper species in the zeolite are Cu(II) ions in the zeolite cages. The contribution of Cu-Cu local structure is suggested for high loading samples. The Cu atoms in the zeolite are more ionic than CuO. The analysis of the catalyst deactivated by SOx treatment suggests the presence of Cu atoms surrounded by SO4 ions which blocks the adsorption of NO molecules.

Increase in the γ-linolenic acid content by solvent winterization of fungal oil extracted fromMortierella genus

Abstract: The fungal oil extracted fromMortierella ramanniana var.angulispora (IFO 8187) was solvent winterized in order to raise the content of γ-linolenic acid (GLA). Effects of winterization conditions (solvent, oil concentration in the solvent and temperature) and changes of glyceride compositions were discussed. The fungal oil was separated into four diglycerides and 17 triglycerides (TG) with high performance liquid chromatography. The predominant species were POO, POP and LOP, whose contents were 24.4, 22.9 and 9.4% of the total TG, respectively. Ethanol at 4°C gave the highest GLA content of 10.5% in spite of lower yield than with acetone at −20°C. The highest separation efficiency for GLA (ηGLA) was 0.27 with acetone at −20°C and 10% oil concentration, resulting in 8.3% of GLA from the fungal oil at 5.7% LGA. In case of lower oil concentration at 5–20%, ηGLA showed higher in the following order: acetone (−20°C)>n-hexane (−20°C)>acetone (4°C)>petroleum ether (−20°C). The winterization process also proved to be effective for the separation of TG type, Sa2U (Sa; saturated fatty acid; U, unsaturated fatty acid) into the crystallized fraction and SaU2 into the liquid fraction. Acetone at −20°C showed higher separation efficiency for triunsaturated TG than the other solvents.

Production of mannosylerythritol lipids by Candida antarctica from vegetable oils

Abstract: Three tested stock-strains of Candida antarctica were found to produce biosurfactants, i.e., mixtures of 4 mannosylerythritol lipids. They were similar to those produced by isolated strain T-34, but differed in the compositions of the mixtures of the lipids. Strain T-34 was the best producer of the lipids as to total amounts. The strain produced the lipids from different vegetable oils, but failed to produce them from n-alkanes or carbohydrates. The supplementation of yeast extract increased the yield of the lipids. Under the optimal conditions in a shake culture, the concentration of the total lipids amounted to about 40 g/l after 8 days. During the cultivation, the composition of the mixture of the lipids was found to change.

Chemical Potential Diagrams for Rare Earth‐Transition Metal‐Oxygen Systems: I, Ln‐V‐O and Ln‐Mn‐O System

Abstract: The thermodynamic properties of double oxides in rare earth-transition metal (V and Mn)-oxygen ternary systems have been collected and evaluated to examine their stability using chemical potential diagrams plotted as log (αA/αB) vs log (P(O2)). The thermodynamic regularities of perovskites, pyrochlores, and other compounds have been discussed in terms of the effective ionic radii across a series of rare earths. The obtained regularities have been used to estimate tentatively the thermodynamic properties of some rare-earth vanadium and manganese oxides.

Modeling of poly(ethylene terephthalate) reactors. IX. Solid state polycondensation process

Abstract: A mathematical model for simulation of industrial process of solid state polycondensation of poly(ethylene terephthalate) (PET) has been developed. The model eliminates errors evident in the earlier models by proper formulation. The model results have been validated by experimental data in the literature. It enables prediction of the influence of particle shape, size, temperature, etc. on the polycondensation process correctly in all different regimes of operation, apart from bringing out the importance of gas-side resistance, influence of carrier gas, etc. for the first time.

Substrate-dependent shift of optimum pH in porcine pancreatic alpha-amylase-catalyzed reactions.

Abstract: Porcine pancreatic alpha-amylase (EC 3.2.1.1, abbreviated as PPA) hydrolyzes alpha-D-(1,4) glucosidic bonds in starch and amylose at random, and the optimum pH for the substrates is 6.9. The optimum pH, however, shifted to 5.2 for the hydrolytic reaction of low molecular weight oligosaccharide substrates such as p-nitrophenyl alpha-D-maltoside, gamma-cyclodextrin, maltotetaitol, and maltopentaitol. The optimum pH for the oligosaccharides consisting of more than five glucose residues, such as maltopentaose and maltohexaitol, was 6.9. From the analysis of the hydrolysates, it was clear that the shift of the optimum pH occurred only when the fifth subsite of PPA in the productive binding modes was occupied by a glucosyl residue of the substrates. The value of Km was independent of pH between 4 and 10 but that of kcat was dependent on pH. The pH profiles of kcat for the above substrates did not fit a simple bell-shaped curve predicted by a two-catalytic-group mechanism. Instead, they were well analyzed theoretically by three pK values and two intrinsic kcat values. Enthalpy changes for the three pK's (4.90, 5.35, and 8.55 at 30 degrees C) were determined from the temperature dependence of pH profiles for maltopentaitol and maltohexaitol to be 0.0, 2.87, and 7.33 kcal/mol, respectively. These results indicate that productive binding modes of the substrates directly affect the catalytic function of the enzyme. From the present thermodynamic analysis and reported three dimensional structure at the active site of PPA [Buisson, G. (1987) EMBO J. 6, 3909-3916], one can assume that a histidyl residue (101, 201, or 299) acts as a proton donor and two carboxyl groups (Asp 197, Glu 233, or Asp 300) act as proton donors or acceptors, and the productive binding mode covering the fifth subsite changes configurations between the catalytic residues and the glucosidic bond hydrolyzed and modulates kinetic parameters depending on pH.

Transport of Lanthanide lons through Cellulose Triacetate Membranes Containing Hinokitiol and Flavonol as Carriers

Abstract: Fluxes of trivalent lanthanide ions across cellulose triacetate membranes were determined by using hinokitiol (HIPT) and flavonol (HFL) as carriers. The transport of the lanthanides was coupled to a flow of hydrogen ions. The effects of added anion and the pH in the source phase, and the plasticizer incorporated in the membrane on the lanthanide flux, were examined. In the case of HIPT, the fluxes for the lanthanides from samarium to lutetium were much higher than those for lanthanum to neodymium. In the transport using HFL, the flux increased with decreasing ionic radius of the lanthanide species. The addition of perchlorate or thiocyanate ions to the source phase resulted in a rise in the lanthanide flux. With decreasing pH difference between the aqueous phases, the fluxes using HIPT decreased gradually while those using HFL decreased rapidly. The flux was affected by the type of plasticizer added to the membrane.