微乳法制备细分散渣油悬浮床加氢催化剂

采用微乳法,通过调整表面活性剂的组成,制备用于渣油悬浮床加氢的细分散催化剂。对制备的催化剂样品进行光学显微镜和等离子分析,结果表明,采用理想的乳化剂配方可以使催化剂均匀稳定分布在渣油原料中,无沉降现象发生。同时,以孤岛常压渣油为原料,在高压釜上考察细分散催化剂的反应性能。试验结果表明,在相同的反应条件下(435 ℃,10 MPa,1 h^－1),同时控制生焦量在允许范围,524 ℃以下液体收率可以提高5～7个百分点,从而进一步证实均匀分散的催化剂具有较高的活性和抑焦性能,具有很好的应用前景和使用价值。     

CVD synthesis of carbon nanotubes using a finely dispersed cobalt catalyst and their use in double layer electrochemical capacitors

Carbon nanotubes (CNT) were obtained by chemical vapour deposition (CVD), decomposing turpentine oil over finely dispersed Co metal as a catalyst at 675 °C. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images reveal that the nanotubes are densely packed and of 10-50 nm in diameter. The XRD pattern of purified CNT shows that they are graphitic in nature. Resistivity measurements of these CNT indicate that they are highly conducting. Hall measurements of CNT reveal that electrons are the majority carriers with a carrier concentration of 1.35×10²⁰ cm⁻³. Cyclic voltammetry (CV) and constant current charging/discharging was used to characterise the behaviour of electrochemical double layer capacitors of purified CNT with H₂SO₄. For CNT/2 M H₂SO₄/CNT, a capacitance of 12 F g⁻¹ (based on the weight of the active material) was obtained.     

The dynamical behavior of catalyst pellets in the limiting cases of finely porous and coarsely porous structures

The pair of partial differential equations conventionally used to describe the dynamical behavior of a porous catalyst pellet is appropiate only in the limiting case when all pore diameters are small compared with mean free path lengths in the reaction mixture. It is here shown that, at the opposite limit, when all pores are large compared with mean free path lengths, this pair of equations must be replaced by three simultaneous partial differential equations. Quantitatively significant differences are found between the stability limits for steady states obtained from the two sets of equations.     

Alkaloidal Glycosidase Inhibitors and Digestive Glycosidase Inhibition in Specialist and Generalist Herbivores of Omphalea diandra

Generalist herbivores of the neotropical liana Omphalea diandra (Euphorbiaceae) were compared to the specialist herbivore, larvae of the uraniid moth Urania fulgens, with respect to their ability to accumulate the alkaloidal glycosidase inhibitors (AGIs) produced by the plant and the resistance of their digestive glycosidases to inhibition by these AGIs. The generalist herbivores did not accumulate the AGI aglycones 2R,5R-dihydroxymethyl-3R,4R-dihydroxypyrrolidine (DMDP) and 2,6-dideoxy-2,6-imino-D-glycero-L-gulo-heptitol (HNJ) to the levels detected in larvae of U. fulgens, which contained 0.05–0.11% dry weight DMDP and 0.17–0.35% HNJ. Glucosides of DMDP and HNJ that were synthesized by O. diandra were either absent from both the generalist and the specialist herbivores or present at low levels (less than 0.01%), even though HNJ-glucoside was often the most abundant AGI in the foliage. Analyses of the herbivores' feces indicated that failure to accumulate AGIs was due to the compounds being metabolized rather than excreted. The digestive glycosidases of U. fulgens larvae were more resistant to inhibition by AGI aglycones than those of the generalist herbivores. Similarly, sucrose and maltose hydrolysis in two of the generalist lepidopteran herbivores, larvae of Panthiades ballus and Theope virgilius, was more resistant to inhibition by DMDP than in larvae of Spodoptera littoralis, a lepidopteran which does not encounter O. diandra in nature. There was little difference in the susceptibility to AGIs of glycosidases from the generalist coleopteran Rhabdopterus fulvipes, which naturally feeds on O. diandra, compared with the coleopteran Dermestes maculatus, which does not. The glucoside of HNJ was found to be a very potent inhibitor of trehalase activity in all the insects examined. AGIs are considered to reduce the nutritional value of O. diandra to nonadapted herbivores rather than be acutely toxic. Nevertheless, U. fulgens does appear to be unique among Omphalea-feeding insects in its ability to accumulate AGIs, suggesting that it gains some advantage from storing these compounds.     

Growth mechanisms of carbon nanofilaments on Ni-loaded diamond catalyst

Nickel-loaded oxidized powdered diamond (Ni/O-Dia) was used for the synthesis of carbon nanofibers (CNFs).CNFs grown at 400 °C, from both CH₄ and C₂H₆ over Ni/O-Dia, had herring-bone type graphene sheets and those grown at 600 °C had tube type graphene sheets. The amount of CNFs was greatly affected by the growth temperature in both CH₄ and C₂H₆. In all the cases, Ni particle was found on the tip end of the grown CNFs.No carbon formation was observed at 650 °C or higher temperature from both CH₄ and C₂H₆, because Ni particles on O-Dia were covered with graphene sheets.Termination of the growth of CNFs was ascribed to the rapid decomposition of hydrocarbons on active Ni surface as compared to the dissolution and diffusion of the carbon on Ni surface into bulk Ni particle to give CNFs on the opposite side of active Ni surface.     

Combustion of a finely dispersed solid fuel in a turbulent flow

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 5, pp. 42–52, September–October, 1990.     

Fluorous Iminoalditols: A New Family of Glycosidase Inhibitors and Pharmacological Chaperones

A collection of new reversible glycosidase inhibitors of the iminoalditol type featuring N‐substituents containing perfluorinated regions has been prepared for evaluation of physicochemical, biochemical and diagnostic properties. The vast variety of feasible oligofluoro moieties allows for modular approaches to customised structures according to the intended applications, which are influenced by the fluorine content as well as the distance of the fluorous moiety from the ring nitrogen. The first examples, in particular in the D ‐galacto series, exhibited excellent inhibitory activities. A preliminary screen with two human cell lines showed that, at subinhibitory concentrations, they are powerful pharmacological chaperones enhancing the activities of the catalytically handicapped lysosomal D ‐galactosidase mutants associated with GM1 gangliosidosis and Morquio B disease.     

Cyclohexane dehydrogenation on a nickel catalyst: Kinetics and catalyst fouling

The main reaction and deactivation kinetics of cyclohexane dehydrogenation in the presence of hydrogen has been investigated at atmospheric pressure over a nickel kieselguhr catalyst in the temperature range 583–623 K. The rate of reaction for the fresh catalyst increased with increasing temperature, cyclohexane and hydrogen partial pressures whereas it decreased with an increase in the benzene partial pressure. The experimental data could be adequately modelled by a power law rate expression. The catalyst activity decreased with run time due to catalyst fouling by coke deposition. The rate of deactivation was independent of cyclohexane partial pressure, increased with increasing benzene concentration and decreased with increasing hydrogen partial pressure. It is postulated that coke is most likely formed by the successive dehydrogenation of benzene.     

Combustion of a finely divided powder of a subgroup IVA metal in hydrogen

Combustion, Explosion, and Shock Waves -     

Microscopic mechanisms for the catalyst assisted growth of single-wall carbon nanotubes

Whatever the synthesis technique used, the growth of ropes of single-wall carbon nanotubes requires the assistance of a metallic catalyst. In this paper, the role played by the catalyst is studied both experimentally and theoretically. Experimentally, the similarities between the samples synthesized from different techniques suggest a common growth mechanism proceeding via the precipitation of excess carbon on metallic nanoparticles. In this paper, the correlation between ropes and catalytic particles is investigated in detail in the case of the Ni-Y catalyst used in the arc discharge technique by combining high resolution transmission electron microscopy, X-ray and electron energy loss spectroscopy. It is shown that the ropes are always found attached to metallic particles about ten times larger than the tube diameter. A further remarkable proof of this relationship is provided by the chemical analyses of the metallic particles. These are found to be free of carbon and to always display the same Ni:Y composition range, whatever the initial Ni:Y composition of the catalyst mixture used in the synthesis, whereas the composition of other particles is highly dispersed. These experimental results support a mechanism of formation based on a vapor-liquid-solid model, in which the tubes of a given bundle nucleate in a cooperative manner and grow at the surface of a same metallic particle. This phenomenological scheme is supported by quantum molecular dynamics simulations which show that carbon atoms are incorporated at the root of a growing tube by a diffusion-segregation process occurring at the surface of the catalytic particle.     

Rare behaviour of a catalyst pellet catalyst dynamics

Temperature overshoots and undershoots were found for a Pd on alumina catalyst pellet in its course towards a new steady state after a change in concentration of one of the reactants ethylene or hydrogen. When cooling the pellet, after heat-up by reaction, with pure hydrogen a sudden temperature peak appears after a short time.A mathematical model is introduced, which can explain the over- and undershoots by slow ad- or desorption on the active sites of the catalyst of one of the reactants.     

Adsorption of alcohols on finely divided powders

The flow micro-calorimeter has been used for the determination of energies of adsorption at monolayer coverage (mcal/g of powder) from solution for a homologous series of long-chain alcohols, the solvent in each case being n-heptane. The results show that the energies increase with increase in length of the carbon chain until the chain has six carbon atoms; the energies then fall to a constant value. The area occupied by one adsorbed molecule increases slowly at first, more rapidly for a chain length of four to eight carbon atoms and then approaches a constant value. The heat of adsorption (kcal/mole of solute adsorbed) rises rapidly at first and smoothes off to a constant value as the length of the carbon chain increases above ten. It is suggested that this indicates that the molecules orientate themselves in the form of a spiral with six carbon atoms on the surface of the solid; this requires a bond angle of 120° which is in agreement with the findings of Calvet & Astruc.     

Glycine-nitrate combustion synthesis of finely dispersed alumina

The possibility of synthesizing different crystalline modifications of alumina Al₂O₃ by combustion reactions of a mixture of aluminum nitrate with glycine has been analyzed. Aggregated powders of γ-Al₂O₃ that do not transform into the corundum structure after annealing at a temperature of 1000°C have been prepared. The influence of the synthesis conditions on the specific surface area, bulk density, porosity, and morphology of alumina particles has been investigated.