Hydrogenation of 3,4-epoxy-1-butene over Cu–Pd/SiO2 catalysts prepared by electroless deposition

Electroless deposition has been used to prepare Cu–Pd/SiO₂ bimetallic catalysts wherein initial Cu coverages are limited only to the pre-existing Pd surface. Cu loading on the Pd surface can be systematically varied by modification of deposition kinetic parameters. In this case deposition time was used as the kinetic variable for the preparation of a series of Cu–Pd catalysts. These materials have been characterized using atomic absorption, CO chemisorption, and FT-IR (adsorption of CO), and then evaluated for the hydrogenation of 3,4-epoxy-1-butene, a functionalized olefin having many potential reaction pathways. Catalyst performance and characterization results suggest that Cu is not distributed in a monodisperse manner on the Pd surface, indicating the existence of autocatalytic deposition of Cu on Cu sites. The FT-IR results suggest that although CO adsorption on all sites is suppressed by Cu addition, initial Cu deposition occurs more readily on certain sites. The bimetallic Cu–Pd sites that are formed exhibit unusually high activity for EpB conversion and formation of unsaturated alcohols and aldehydes. This bimetallic effect on catalyst activity and selectivity is best explained, not by the existence of either ligand or ensemble effects, but rather by the bifunctional nature of the Cu–Pd sites present on the surface of these catalysts.     

Atomization of metal fluorides for enhanced flow characteristics of a multicomponent powder

The National Aeronautics and Space Administration's (NASA's) PS304 coating is a plasma spray deposited tribological coating with feedstock composed of NiCr, Cr₂O₃, Ag and BaF₂-CaF₂ powders. The effects of rounded BaF₂-CaF₂ particles on the gravity-fed flow characteristics of PS304 feedstock have been investigated. The BaF₂-CaF₂ powder was fabricated by water atomization using four sets of process parameters. Each of these powders was then characterized by microscopy and classified by screening to obtain 45-106 μm particles and added incrementally from 0-10 wt.% to the other constituents of the PS304 feedstock, namely nichrome, chromia and silver powders. The relationship between feedstock flow rate, measured with the Hall flowmeter, and concentration of fluorides was found to be linear in each case. The slopes of the lines were between those of the linear relationships previously reported using angular and spherical fluorides and were closer to the relationship predicted using the rule of mixtures. The results offer a fluoride fabrication technique potentially more cost-effective than gas atomization processes or traditional comminution processes.     

'Polymorph Method' Determination of Monoclinic Zirconia in Partially Stabilized Zirconia Ceramics

The polymorph method, which provides phase analysis from a small number of integrated intensities in a powder diffraction scan, is adapted for the determination of monoclinic zirconia in a mixture with cubic, tetragonal. and orthorhombic zirconias and the γ-phase (Mg₂Zr₅O₁₂). Such a mixture is representative of Mg-PSZ after subeutectoid aging. The quantitative determination of the monoclinic depends in principle on a knowledge of the relative amounts of the other phases present in the mixture. It is demonstrated, however, that without this knowledge, even in complex mixtures, the traditional polymorph method analysis gives an acceptable estimate of the monoclinic fraction in the sample.     

Methods of Modifying the Brittle Behavior of Cementitious Composites

We put forward effective methods of increasing the tensile strain of cementitious composites with 2% PVA fiber and high fly ash content. The test results show that curing condition has a significantly effect on the tensile performance. It is approved that the specimens incorporated appropriate volume fraction rubber powder and lightweight aggregate greatly increase the tensile strain of composites at medium-term age, but indefinitely at long-term age. To a certain extent, EVA can limitedly enhance the tensi...     

The existence of a soluble plasmalogenase in guinea pig tissues

The distribution of plasmalogenase for the hydrolysis of 1-alkenyl-2-acyl-sn-glycero-3-phosphoethanolamine (plasmenylethanolamine) in the subcellular fractions of guinea pig tissues was examined. Plasmalogenase activity was found in high abundance in the cytosolic fractions of the brain and the heart. Assessment of microsomal marker enzyme activities in the cytosolic fraction revealed that plasmalogenase activity in the cytosol was not due to microsomal contaminations. The characteristics of the cytosolic plasmalogenase were very similar to the microsomal enzyme with respect to the pH profile of the reaction, the presence of divalent cations and K_m values for plasmenylethanolamine. However, the cytosolic enzyme was slightly less stable at 55°C than the microsomal enzyme. Cytosolic enzyme activity was eluted as a broad peak in Sepharose 6B chromatography with an average molecular weight of 250,000. Our results demonstrate that most of brain plasmalogenase activity is soluble which makes the brain cytosol an excellent source to initiate the purification of this enzyme.     

Photopolymer kinetics using light intensity gradients in high-throughput conversion analysis

Light intensity gradients and light exposure time gradients were combined to produce contours of constant dose on a sample substrate. These polymerized samples were subsequently analyzed using high-throughput Fourier transform infrared spectroscopy to measure conversion as a function of both gradients. Three (meth)acrylate monomers were analyzed over light doses ranging from 0 mJ/cm² to 920 mJ/cm², demonstrating that in thin films, higher light intensities at a constant light dose produce higher conversion due to a decreased oxygen inhibition time and larger thermal excursions. At a light dose of 75 mJ/cm², the conversion of 2-ethylhexyl acrylate increases from 40 ± 2% at a light intensity of 0.9 mW/cm² to 59 ± 3% at 7.2 mW/cm². The two acrylate monomers exhibited rapid photopolymerization up to a specific conversion, after which additional radiation dose produced only marginal increases in overall conversion. For hexanediol diacrylate, a light dose of 300 mJ/cm² was the minimum amount required to reach the maximum conversion over the entire range analyzed. For the dimethacrylate system, a similar effect was seen, with a reduced oxygen inhibition time and conversion above 70% showing a similar conversion at a constant light dose of 500 mJ/cm². In all three systems, dose contours were used to determine a range of light intensities at which a statistically similar conversion would occur for a specified light dose.     

Organoiron Polyelectrolytes: Synthesis and Characterization of Cationic Cyclopentadienyliron Complexes of Polyarylether-Imines

The synthesis of an aromatic ether complex of cyclopentadienyliron containing two terminal aldehyde groups was achieved via metal-mediated nucleophilic aromatic substitution reactions. This dialdehyde monomer was subsequently reacted with a variety of aliphatic and aromatic diamines to produce the corresponding soluble cationic organoiron polyether-imines. These cationic organometallic polymers were characterized using IR, ¹H, and ¹³C NMR, viscosity and thermogravimetric analysis. Viscosity measurements showed that these polymers exhibited polyelectrolyte effects in DMSO solutions. Thermogravimetric analysis showed that decoordination of the iron moieties occurred at about 300°C for polymers with aliphatic spacers in their backbones, while the cyclopentadienyliron moieties were cleaved from the polymers with aromatic spacers in their backbones at about 200°C. Photolytic demetallation of the organoiron polymers resulted in the removal of the pendent cyclopentadienyliron moieties and allowed for the isolation of their organic analogs. While the organoiron polymers were soluble in polar organic solvents, the corresponding organic polymers exhibited very limited solubilities or were insoluble. The organic polymers had glass transition temperatures between 101 and 120°C     

Ring position in cyclopropene fatty acids and stearic acid desaturation in hen liver

Four cyclopropene fatty acids, having the double bond of the cyclopropene ring at the 8,9, 9,10, 10,11 and 11,12 positions, respectively, were tested as inhibitors of stearic acid desaturation by the desaturase enzyme system of hen liver. The first three were powerful inhibitors, but the last was not. The cyclopropene acids with the 9,10 and 10,11 double bonds were equally strong inhibitors, while the acid with the 8,9 double bond was less effective. To account for the specificity of those cyclopropene fatty acids in which the C9 or C10 carbon atom is included in the cyclopropene ring, it is suggested that the conformation and structure of the CoA derivatives of these acids is such that they can irreversibly occupy the site on the enzyme responsible for 9,10-desaturation.     

Kinetics of Thermal Dehydroxylation and Carbonation of Magnesium Hydroxide

The kinetics of simultaneous dehydroxylation and carbonation of precipitated Mg(OH)₂ were studied using isothermal and nonisothermal thermogravimetric analyses. Specimens were analyzed using X-ray diffraction, transmission electron microscopy, and through measurements of the volume of carbon dioxide evolved in a subsequent reaction with hydrochloric acid. From 275° to 475°C, the kinetics of isothermal dehydroxylation in helium were best fit to a contracting-sphere model, yielding an activation energy of 146 kJ/mol, which was greater than values reported in the literature for isothermal dehydroxylation under vacuum (53–126 kJ/mol). The carbonation kinetics were complicated by the fact that dehydroxylation occurred simultaneously. The overall kinetics also could be fit to a contracting-sphere model, yielding a net activation energy of 304 kJ/mol. The most rapid carbonation kinetics occurred near 375°C. At this temperature, Mg(OH)₂ underwent rapid dehydroxylation and subsequent phase transformation, whereas thermodynamics favored the formation of carbonate. During carbonation, MgCO₃ precipitated on the surface of disrupted Mg(OH)₂ crystals acting as a kinetic barrier to both the outward diffusion of H₂O and the inward diffusion of CO₂.     

IR transmission prediction,processing, and characterization of dense La2Ce2O7

High-throughput computation, based on density functional theory (HT-DFT), is used to predict the bounds for optical transparency, from the ultraviolet to the infrared, for materials in the pyrochlore family. The HT-DFT approach adopted here uses an initial screening from Materials-Project database, with millions of calculated properties. Band gaps and phonon spectra were calculated from selected pyrochlore crystal structures taken from the Materials Project database. Short and long wavelength bounds for optical transparency were calculated for chemistries with stable, cubic structures. The calculations predict that La₂Ce₂O₇ has one of the broadest range of transparency for the pyrochlore family. Based on these calculations, dense polycrystalline samples of La₂Ce₂O₇ were produced by sintering and hot-isostatic pressing. Transparency was characterized by methods that did not require large samples with high optical quality, obtaining 7.15 and 7.5 µm at 95% and 90% normalized transmittance, respectively. Bandgap calculations suggest a lower bound of UV transparency cut-off of 0.3 µm. The infrared wavelength cut-off is higher than that reported for other pyrochlores, and higher than for yttria, zirconia, or other common infrared transparent ceramics. We discuss our prediction and characterization methods as well as the suitability of pyrochlores for mid- and far-infrared optical applications.