Composition of Pd-La/α-Al2O3 catalysts

The objective of this study is to investigate the structure of the Pd-La/-Al₂O₃ catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPRd) were used as characterization techniques. Contrary to the assertions in the literature, XRD studies conducted on La/-Al₂O₃ composite oxides and Pd-La/-Al₂O₃ catalysts show that Pd catalyzes the solid state reaction between A1₂O₃ and Al₂O₃ to form LaAlO₃. TPRd studies conducted on Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaAlO₃, and Pd-La/-Al₂O₃ catalysts suggest that Pd in the Pd-La/-Al₂O₃ catalyst interacts more strongly with LaAlO₃ than with -Al₂O₃. Reaction studies were conducted to investigate the activity of Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaA10₃, and Pd-La/-Al₂O₃ catalysts for nitric oxide (NO) reduction. These studies show that Pd/LaAlO₃ catalysts are most active for NO removal at stoichiometric and under net reducing conditions.     

Phase transitions and dimensional and morphological changes in an “Aluminum Hydroxide-Alumina” system under a shock-wave action

A method is proposed to study the sequence of phase transitions in powdered materials under a shock-wave action. It is shown that the aluminum hydroxide-alumina system has the following sequence of phase transformations under a shock-wave action: bayerite boehmite -Al₂O₃ -Al₂O₃. It is found that there are no transitional high-temperature modifications of alumina. A method is developed for obtaining a submicron alumina powder, which allows obtaining materials with a controlled phase composition, including a thermodynamically stable -modification of Al₂O₃. The specific features of the morphological structure and the phase and structural characteristics of powders after a shock-wave action are considered.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 110–119, January–February, 2005.     

Effect of the crystalline from of Al2O3 on the interaction and sintering of large-crystal quartzite and disperse alumina

It is established that the amount of mullite and the value of the open porosity of specimens increase in the sequence -Al₂O₃(+)-Al₂O₃-Al₂O₃Al₂O₃ · 3H₂O. The apparent density and the ultimate compressive strength increase in the reverse direction. Active modifications of alumina (hydrargillite, -Al₂O₃) stimulate mullite formation, which is accompanied by an increase in the open porosity to 40% and a decrease of the mechanical strength to 8–12.5 MPa, and high (up to 12%) linear shrinkage. High-quality, dense, strong refractories can be produced in a single firing from coarse-grained quartzite and finely disperse corundum and alumina in the form of -Al₂O₃.Translated from Ogneupory, No. 10, pp. 18 – 20, October, 1994.Eastern Institute of Refractories.     

Anisotropic structure analysis for cobalt oxides on α-Al2O3(0001) by polarized total-reflection fluorescence extended X-ray absorption fine structure

Anisotropic structure analyses for [CoO_x]/-Al₂O₃ (0001) and [Co₃O₄]_n /-Al₂O₃ (0001) which were derived from Co₂(CO)₈/-Al₂O₃ (0001) were performed by a polarized total-reflection fluorescence extended X-ray absorption fine structure (EXAFS) technique. Both s- and p-polarized EXAFS data revealed that the cobalt atoms of [CoO_x] were located on three-fold hollow sites of -Al₂O₃ (0001) in a monomer form and that a thin spinel structure [Co₃O₄] grew with the (001) plane parallel to -Al₂O₃ (0001).     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Behavioral and neurosensory responses of the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae), to fluorinated analogs of aldehyde components of its pheromone

Competitive field tests with -fluorinated analogs of compounds III and IV (III--F and IV--F, respectively) of the boll weevil,Anthonomus grandis Boh., aggregation pheromone showed these compounds, when combined with the other pheromone components [(±)-I and II], to be as attractive as grandlure [(+)-I, II, and III+IV]. Dose-response curves constructed from electroantennograms of male boll weevils to serial stimulus loads of III, IV, III--F, IV--F, and the corresponding acyl fluorinated analogs (III-acyl-F and IV-acyl-F) showed the -fiuorinated analogs to be as active as the pheromone components (threshold=0.1 g), while the acyl fluorinated analogs had a 10-100 x higher threshold (=1-10 g). Single-neuron recordings showed that IV neurons and II neurons (Dickens, 1990) responded to IV--F and III--F, respectively, while IV-acyl-F and III-acyl-F were inactive. Since a previous study showed compounds I, II, and IV to be essential for behavioral responses in the field, it seems likely that the activity of the -fluorinated analogs observed here is due to the stimulation of IV neurons by IV--F as indicated in single neuron recordings.     

Catalytic oxidation of methanol to methyl formate over silver – a new purpose of a traditional catalysis system

Catalytic reaction was performed in the unregarded temperature region over silver catalysts with long catalytic lifetime for the conversion of methanol to methyl formate. O-saturated or O-saturated silver catalysts were studied individually to identify the roles of O, O in the oxidative esterification of methanol over an unsupported polycrystalline silver catalyst. A synergic process is proposed based on the coexistence of -oxygen species and -oxygen species on the surface of polycrystalline silver at about 573 K.     

Enhancement of βα-recrystallization in β-form isotactic polypropylene during heating after roll deformation

Summary -form isotactic polypropylene shows -recrystallization behavior (recrystallization from - to -form) during slow heating. This is enhanced by deformation. -form specimen with uniaxially oriented lamellae was deformed by rolling, and -recrystallization was studied by DSC and x-ray diffraction. The result showed that (1) — recrystallization is promoted with the degree of deformation. (2) Deformed specimen shows -recrystallization from considerably low temperature compared with the undeformed one. (3) The recrystallized -form is c-axis-oriented along the roll direction. From these results the -recrystallization mechanism was discussed in view of -nucleus formation by deformation.     

Ultrafine α-Al2O3. Explosive Method of Synthesis and Properties

An explosive method for producing ultrafine -Al₂O₃ is developed and optimal synthesis parameters are determined. Particles of ultrafine -Al₂O₃ have a spherical shape and are separated from one another. The size distribution is log-normal (number-averaged size 70 nm and variance 1.9). Special features of phase transitions in ultrafine aluminum oxide under shock-wave action are studied. Results of x-ray phase analysis suggest stabilization of the new high-pressure phase -Al₂O₃ with a face-centered cubic lattice with a parameter a = 8.53 Key words: metastability, corundum, shock-wave synthesis, surface, modification.     

Isolation and identification of male medfly attractive components inLitchi chinensis stems andFicus spp. stem exudates

Short-range attraction/feeding stimulation of male Mediterranean fruit flies [Ceratitis capitata (Wiedemann), (Diptera: Tephritidae)] to a stem extract of a host plant,Litchi chinensis Sonn. (Sapindaceae), and to milky exudates from stems of nonhost plants,Ficus retusa L. andF. benjamina L. (Moraceae), were attributed to the presence of the sesquiterpene -copaene. The presence of -copaene in the milky exudate from stems ofF. benghalensis L. is also suggested as eliciting similar behavioral responses in male medflies. The presence of minor quantities of -ylangene in the plants and its contributory effects to the behavioral response of male medflies is discussed. Short-range attraction/feeding stimulation of male medflies to equal amounts of -ylangene-free -copaene samples (94.5%+), prepared from -copaene-enriched angelica seed oil and copaiba oil, respectively, showed no difference in intensity of response. -Ylangene elicited a slightly less intense response for male medflies than -copaene.Names of products in this paper are included for the benefit of the reader and do not imply endorsement or preferential treatment by USDA.     

Response of the European elm bark beetle,Scolytus multistriatus (Coleoptera: Scolytidae), to isomers and components of its pheromone

Laboratory bioassays (two methods) and field tests demonstrated synergistic action of the three components [(–)-4-methyl-3-heptanol (I); (–)-2,4-dimethyl-5-ethyl-6,8-dioxabicylo[3.2.1]octane (-multistriatin) (II); and (–)--cubebene (III)] of the pheromone bouquet ofScolytus multistriatus. Individually and in pairs the components were slightly attractive; I+II was clearly the most active doublet. Indirect evidence indicates that only one of the four enantiomers of I is active. Of the , , and isomers of II, only the is active. With the addition of compound I, slightly attractive extract from mated females became nearly as active as extract from virgin females.     

Mass transfer in an annular electrodialysis cell in pulsating flow

The effect of pulsating flow on the mass transfer in an annular electrodialysis cell has been studied in terms of the limiting current. The results indicate that the limiting current is influenced by the fluid velocity, the pulsation amplitude and the pulsation frequency, giving an increase of 400% with respect to the steady state. For a given amplitude, the dimensionless velocity, 0 (0 = a/v), can be taken as a representative parameter of the pulsation effect on the mass transfer. The fractional increase in the Sherwood number in pulsating flow with respect to the steady state has been correlated in terms of the dimensionless velocity, 0, and the Stokes number, 1 (1 = Deq (/)1/2), giving the correlation:     

Small Amounts of Rh-Promoted Ni Catalysts for Methane Reforming with CO2

Small amounts of Rh-promoted Ni/-Al₂O₃ catalysts possessed higher activity than pure Ni/-Al₂O₃, Rh-Al₂O₃ catalysts and exhibited excellent coke resistance ability in methane reforming with CO₂. XRD, H₂-TPR, CO₂-TPD and coking reaction (via CH₄ temperature-programmed decomposition) indicated that Rh improved the dispersion of Ni, retarded the sintering of Ni and increased the activation of CO₂ and CH₄ on the surface of catalyst.     

Asymmetric structure analysis of active surface-sites by in situ polarized total-reflection fluorescence EXAFS

An in situ polarization-dependent total reflection fluorescence yield EXAFS system has been developed to analyze the asymmetric structures of catalytically active metal sites on single crystal surfaces. This technique separately reveals the bonding feature parallel and perpendicular to the support surface. The systems of Cu ion on -quartz(0001), Co oxide on -alumina(0001), and Pt₄ on -alumina(0001) were investigated as model surfaces of supported catalytic systems. The location of Cu sites on -quartz(0001), the epitaxial growth mode of Co₃O₄ on -alumina(0001), and the Pt raft structure with metal-support interaction in Pt₄ / -alumina(0001) were observed.     

Musk deer (Moschus moschiferus): Reinvestigation of main lipid components from preputial gland secretion

The qualitative and quantitative composition of the principal lipid constituents of Siberian musk deer (Moschus moschiferus) preputial gland secretion, main odor carriers and potential precursors of odorous substances, was investigated by means of high-performance liquid chromatography. Free fatty acids and phenols (10%), waxes (38%), and steroids (38%) were found to be the main groups of the secretion lipids. Cholestanol (I), cholesterol (II), androsterone (III), ⁴-3-hydroxy-17-ketoandrostene (IV), 5, 3-hydroxy-17-ketoandrostane (V), 5, 3, 17-dihydroxyandrostane (VI), 5, 3, 17-dihydroxyandrostane (VII), and 5, 3, 17-dihydroxyandrostane (VIII) were isolated from the steroid fraction and their structures confirmed by IR, PMR, and mass spectra. 3-Methylpentadecanone (muscone) was not identified among the secretion lipids. Preputial gland secretion stimulated sex behavior of musk deer females.     

Identification and Function of Prothoracic Exocrine Gland Steroids of the Dytiscid Beetles Graphoderus cinereus and Laccophilus minutus

The chemical composition of the prothoracic defensive secretion of the water beetles Graphoderus cinereus and Laccophilus minutus was examined by gas chromatographic–mass spectrometric analysis of trimethylsilylated gland extracts. The main components are 3,11-dihydroxy-5-pregnan-20-one in G. cinereus and 3,12-dihydroxy-5-pregnan20-one in L. minutus. Fully saturated pregnanes have not been found in the prothoracic defensive glands of dytiscids before. Based on tests with synthetic compounds, their biological role was examined in a feeding assay with the minnow Phoxinus phoxinus. Agar pellets containing either steroid strongly deterred feeding.     

Synthesis and characterization of α-methylstyrene-butadiene-α-methylstyrene linear block copolymers

Summary -methylstyrene-butadiene- -methylstyrene linear block copolymers with a pure block structure were prepared by sec-butyllithium and coupling agent in a four-step process. Their morphology is built up of microdomains of poly- -methylstyrene, including the unbonded segments, dispersed in a polybutadiene matrix. Cylindrical domains arranged in a hexagonal lattice or irregularly shaped domains in a disordered phase are observed, depending on the molecular weight of the poly- -methylstyrene segment.     

Soldier defense secretions of malaysian free-ranging termite of the genusLacessititermes (Isoptera,Nasutitermitinae)

Soldiers of free-ranging termites of the genusLacessititermes (Isoptera, Nasutitermitinae) secrete from their frontal glands a mixture of monoterpenes, sesquiterpenes, and diterpenes.Lacessititermes ransoneti, L. laborator, andL. species A produce species-specific secretions, the composition being most complex forL. laborator. Apart from known mono- and dihydroxytrinervitadienes, the following new diterpenes were isolated and tentatively assigned as trinervita-1(15),8(19)-dien-2,3,9,14-tetraol 2,3,14-O-triacetate, trinervita-1(15),8(19)-dien-2,3,9,14-tetraol 2,3,14-O-triacetate, 2,3,9, 14-tetraacetoxy-1 (15), 8(19)-trinervitadiene, and 2,3,11,13-tetraacetoxy-1(15),8(19)-trinervitadiene. Data on intragenus chemical variations were subjected to canonical discriminant analysis and genetic distances among the species were calculated to depict intragenus identities and affinities.     

Crystallization and melting of <Emphasis Type="Italic">α</Emphasis> and <Emphasis Type="Italic">β</Emphasis> phases in bulk syndiotactic polystyrene as monitored in situ via high-temperature wide-angle X-ray diffraction

Direct and non-intrusive observations of crystallization and melting behavior of and polymorphs in bulk syndiotactic polystyrene were made by means of temperature-programmed x-ray diffraction. Results indicated that the highest sustainable temperature identifiable via wide-angle x-ray diffraction using stepwise annealing at increasingly higher temperatures (T _a) for the perfected (with the initial crystallization temperature T _c = 245 °C, followed by annealing at stepwise increased T _a above 250 °C) phase may be at least 286 °C. In a similar manner, the highest sustainable temperature of the perfected (with T _c = 265 °C, followed by annealing at stepwise increased T _a above 275 °C) phase may be at least 280 °C. These observations suggest complete melting should occur only above the respective sustainable temperatures. It thus follows that equilibrium melting of the and the phases should occur at temperatures higher than 286 and 280 °C, respectively. Perfection of the less ordered form into the better ordered form within the family is observed to occur in the vicinity of 270 °C; no evidence of transformation between and phases is identified.     

Cure monitoring via different techniques: Isothermal cure of an epoxy-novolac molding compound

The isothermal cure of an epoxy-novolac molding compound was studied by means of Fourier-transform infrared spectroscopy (FTIR) and dielectrometry (DE). Results obtained were compared with previous differential scanning calorimetric (DSC) observations. The behavior of epoxide conversion (_FTIR) measured via FTIR was found similar to (but not exactly coinciding with) the extent of cure (_DSC) determined previously by means of DSC. As for the DE analysis, directly measurable properties such as permittivity () and loss factor () varied in a complicated manner during the course of cure, showing strong dependence on both temperature and frequency. Other dielectric parameters (such as ionic conductivity, relaxed permittivity, and characteristic relaxation time) previously suggested in the literature as suitable for cure monitoring purposes were found difficult to determine within the limited frequency range (10⁰ to 10⁴ Hz) here. With some arbitrariness, the relative drop in log (at 100 Hz) was taken as an index (_DE) for the extent of cure. It was observed that _DE behaves in a manner similar to _FTIR and _DSC Comments on the application of these three techniques in the characterization of thermosetting systems were given.