Enhanced hydrogen storage in Ni/Ce composite oxides

The properties of dried (but not calcined) coprecipitated nickel ceria systems have been investigated in terms of their hydrogen emission characteristics following activation in hydrogen. XRD and BET data obtained on the powders show similarities to calcined ceria but it is likely that the majority of the material produced by the coprecipitation process is largely of an amorphous nature. XPS data indicate very little nickel is present on the outermost surface of the particles. Nevertheless, the thermal analytical techniques (TGA, DSC and TPD-MS) indicate that the hydrogen has access to the catalyst present and the nickel is able to generate hydrogen species capable of interacting with the support. Both unactivated and activated materials show two hydrogen emission features, viz. low temperature and high temperature emissions (LTE and HTE, respectively) over the temperature range 50 and 500 degrees C. A clear effect of hydrogen interaction with the material is that the activated sample not only emits much more hydrogen than the corresponding unactivated one but also at lower temperatures. H(2) dissociation occurs on the reduced catalyst surface and the spillover mechanism transfers this active hydrogen into the ceria, possibly via the formation and migration of OH(-) species. The amount of hydrogen obtained (~0.24 wt%) is approximately 10x higher than those observed for calcined materials and would suggest that the amorphous phase plays a critical role in this process. The affiliated emissions of CO and CO(2) with that of the HTE hydrogen (and consumption of water) strongly suggests a proportion of the hydrogen emission at this point arises from the water gas shift type reaction. It has not been possible from the present data to delineate between the various hydrogen storage mechanisms reported for ceria.     

Co- and counter-current spontaneous imbibition into groups of capillary tubes with lateral connections permitting cross-flow

A model for co- and counter-current imbibition through independent capillaries has already been developed and experiments conducted to verify the theory [E. Unsal, G. Mason, N.R. Morrow, D.W. Ruth, J. Colloid Interface Sci. 306 (2007) 105]. In this paper, the work is extended to capillaries which are connected laterally and in which cross-flow can take place. The fundamental pore geometry is a rod in an angled round-bottomed slot with a gap between the rod and a capping glass plate. The surfaces of the slot, rod and plate form capillaries and interconnecting passages which have non-axisymmetric cross-sections. Depending on the gap size either (i) a large single meniscus, (ii) two menisci one on each side of the rod, or (iii) three menisci, one between the rod and the glass additional to the ones on each side can be formed. A viscous refined oil was applied to one end of the capillaries and co-current and counter-current spontaneous imbibition experiments were performed. The opposite end was left open to the atmosphere for co-current experiments. When the gap between the rod and the plate was large, the imbibing oil advanced into the tubes with the meniscus in the largest capillary always lagging behind the two menisci in the other two smaller capillaries. For counter-current imbibition experiments the open end was sealed and connected to a sensitive pressure transducer. In some experiments, the oil imbibed into the smaller capillaries and expelled air as a series of bubbles from the end of the largest capillary. In other experiments, the oil was allowed to imbibe part way into the tubes before counter-current imbibition was started. The meniscus curvatures of the capillaries have been calculated using the Mayer and Stowe-Princen method for different cell slot angles and gap sizes using a value of zero for the contact angle. These values have been compared with actual values by measuring the capillary rise in the tubes; agreement was very close. A model for co-current and counter-current imbibition has also been developed. The significance of this model is that some hydraulic/capillary properties are common for both co-current and counter-current imbibition. The experiments give an illustration of behavior expected in a real porous material and verify the importance of the 'perfect cross-flow' modification to the 'bundle of parallel tubes' model.     

Enantioselective determination of modafinil in pharmaceutical formulations by capillary electrophoresis, and computational calculation of their inclusion complexes

A fast capillary electrophoretic method is described for the separation and determination of the enantiomers of the novel wake-promoting agent, modafinil. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, buffer concentration, voltage and temperature. Good chiral separation of the racemic mixture was achieved in less than 5 min with resolution factor Rs?=?2.51, using a bare fused-silica capillary and a background electrolyte (BGE) of 25 mM H₃PO₄?1 M tris solution; pH 8.0; containing 30 mg mL^?1 of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in normal polarity mode at 25 ^?C, 18 kV and using hydrostatic injection. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were included. The developed method was successfully applied to the assay of enantiomers of modafinil in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the modafinil enantiomers.     

Europium(III) macrocyclic complexes with alcohol pendant groups as chemical exchange saturation transfer agents

Paramagnetic lanthanide(III) complexes that contain hyperfine-shifted exchangeable protons offer considerable advantages over diamagnetic molecules as chemical exchange saturation transfer (CEST) agents for MRI. As part of a program to investigate avenues to improve the sensitivity of such agents, the CEST characteristics of europium(III) macrocyclic complexes having appended hydroxyethyl groups were investigated. The CEST spectrum of the asymmetrical complex, EuCNPHC3+, shows five distinct peaks for each magnetically nonequivalent exchangeable proton in the molecule. The CEST spectra of this complex were fitted to NMR Bloch theory to yield exchange rates between each of six exchanging proton pools (five on the agent plus bulk water). Exchange between the Eu3+-bound hydroxyl protons and bulk water protons was slow in dry acetonitrile but accelerated incrementally upon stepwise addition of water. In pure water, exchange was too fast to observe a CEST effect. The utility of this class of europium(III) complex for CEST imaging applications is ultimately limited by the small chemical shifts induced by the hydroxyl-appended ligands of this type and the resulting small Deltaomega values for the exchangeable hydroxyl protons.     

Prediction of gas tungsten arc welding properties in mixtures ofargon and hydrogen

A theory of gas tungsten arc welding (GTAW) arcs that treats the tungsten electrode, the arc, and the workpiece as a unified system has been applied to make predictions in two dimensions of the temperature distributions in the arc, the tungsten cathode, and the workpiece, for any given arc current and gas mixture. Predictions of arc temperatures, radii, and voltages are compared for argon and mixtures of argon and hydrogen. It is found that arcs in gas mixtures containing hydrogen are more constricted and have a higher maximum temperature and arc voltage than arcs in pure argon. The addition of hydrogen also significantly increases the volume of molten material in the weld pool due to the higher thermal conductivity of argon-hydrogen mixtures at temperatures at which molecules of hydrogen dissociate. Predictions are also compared for workpieces of steel and aluminum. The volume of molten material is very much less for aluminum, despite its lower melting point, because of the higher thermal conductivity of aluminum. Predicted arc voltages as a function of current for a mixture of 10% hydrogen in argon are in good agreement with experimental results     

Crystal and molecular structure of the triflate salt of diprotonated 1,4,8,11-tetrakis(2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane, [C10H22N4(CH2CH2OH)4 2+]−[CF3SO3 −]2: geometry of a diprotonated octadenate ligand

The title complex crystallizes in the centrosymmetric monoclinic space group P2₁/n with Z=2. The cation is the diprotonated derivative of the neutral octadentate macrocyclic ligand C₁₀H₂₀N₄(CH₂CH₂OH)₄; the two protonated nitrogen atoms are as far apart as is possible in the 14-membered ring (1-and 8-positions) so as to minimize electrostatic repulsions. Each of the [C₁₀H₂₂N₄(CH₂CH₂OH)₄ ²⁺] cations is involved in hydrogen bonding (through the four hydroxy groups) to oxygen atoms on four different peripheral [CF₃SO₃ ⁻] anions.     

Simulation calculation of dielectric constants: Comparison of methods on an exactly solvable model

A mean spherical model of classical dipoles on a simple cubic lattice of sideM=2N+1 sites is considered. Exact results are obtained for finite systems using periodic boundary conditions with an external dielectric constant and using reaction field boundary conditions with a cutoff radiusR _c N and an external dielectric constant. The dielectric constant in the disordered phase is calculated using a variety of fluctuation formulas commonly implemented in Monte Carlo and molecular dynamics simulations of dipolar systems. The coupling in the system is measured by the parametery=4 ²/9kT, where ² is the fixed mean square value of the dipole moments on the lattice. The system undergoes a phase transition aty2.8, so that very high dielectric constants cannot be obtained in the disordered phase. The results show clearly the effects of system size, cutoff radius, external dielectric constant, and different measuring techniques on a dielectric constant estimate. It is concluded that with periodic boundary conditions, the rate of approach of the dielectric constant estimate to its thermodynamic limit is asN ^–2/3 and depends only weakly on. Methods of implementing reaction field boundary conditions to give rapid convergence to the thermodynamic limit are discussed.