An Au/Fe2O3 catalyst prepared using a two-stage calcination procedure achieves target conversion and selectivity for the competitive oxidation of dilute CO in the presence of moist excess H2 and CO2.

5336partitioning in the case of this relatively small hydrophilic monocation compared to the distinct binding observed with the larger, more hydrophobic C B P underlines the role of hydrophobic factors and once again reinforces the idea that these cations as well as probably many other polar organic molecules are solubilized or J. Am. Chem. SOC. 1981, 103, 5336-5341 interact with micelles by binding at hydrophobic-hydrophilic interfaces.Abstract: A simple theory based on electrochemical principles is presented which predicts some of the catalytic properties of the widely used colloidal metal dispersions. The theory has been specifically applied to the case of photocatalytic water reduction to H2. The model assumes that the kinetic properties of the system are governed by the current-potential curves of the half-reactions and that the reaction velocity can be determined by finding the common potential at which the current attributable to the mediator (e.g., methyl viologen) oxidation is equal to that for proton reduction at the metal surface. The effects of pH, mediator potential, and colloid size and composition can be predicted. These predictions have been experimentally verified with methyl viologen radical cation generated electrochemically and photochemically (via the Ru(bpy)?+-N-phenylglyche system) and with other mediators at colloidal dispersions of several metals.

Au/Fe 2 O 3 catalysts prepared using co-precipitation are described and discussed for the preferential oxidation of CO in the presence of H 2 , H 2 O and CO 2 . A catalyst prepared using a two-stage calcination procedure (400 uC followed by 550 uC) achieves target conversion and selectivity (.99.5% CO conversion and .50% selectivity, based on O 2 , for the competing conversion of H 2 with O 2 at 80-100 uC) for the competitive oxidation of dilute CO in the presence of moist excess H 2 and CO 2 . The effect of the preparation method of the uncalcined precursor is described and the effects of calcination on the catalyst activity in the absence of H 2 , CO 2 and H 2 O is initially explored. The catalysts are characterised in detail using electron microscopy (TEM), X-ray photoelectron spectroscopy and Mo ¨ssbauer spectroscopy. For the target conversion to be achieved, it is necessary that the activity for the reverse water gas shift activity (CO 2 + H 2 A CO + H 2 O) of the catalyst is suppressed, since under the fuel cell conditions this reaction reforms CO at high CO conversions due to the presence of excess CO 2 and H 2 . It is proposed that the two stage calcination procedure removes active sites for the water gas shift reaction whilst retaining active sites for preferential CO oxidation.

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15 431 448 20 431 431 acetic acid-chloroform mixture.In almost all cases, 5 ml. of the solvents tested were miscible with 20 ml. of acetic acid-chloroform.Recovery of peroxide was quantitative when as little as 20% by volume of acetic acidchloroform was present in the solvent mixture. It should therefore be possible to determine peroxide groups on polymers and other organic solids if the solution of the material is compatible with the minimum amount of acetic acid-chloroform required for the reaction of the peroxide with iodide.Attempts to determine di-ferf-butyl peroxide by using HC1 to increase the acidity were unsuccessful. Ten milligrams of this peroxide gave a pale yellow 2 hours after solution in 1 to 1 HC1 and the addition of KI.

The room-temperature transmittance of KMgF 3 and MgF 2 have been measured from 800 to 70 cm" 1 . Reflectance measurements were made over a wider range in the far infrared and the data have been analyzed using the Kramers-Kronig relationship to obtain the dielectric dispersion of these materials. Three resonances were observed for KMgF 3 and four were observed for MgF 2 as required by standard group theory and these have been related to presumed normal modes of vibration of the crystals.

Abstract-We have measured the absorption, gain and spontaneous emission spectra of GaInNAsSb (3.3%N), GaInNAs (0.5%N) and GaInAs quantum well structures to compare their merits as laser gain media. The parameters describing the relations between peak gain and current provide only limited insight. From the analysis of absorption spectra we have determined the intrinsic properties of the structures, represented by the product [reduced density of states × matrix element × overlap integral], taking account of differences in operating wavelength, well width and confinement. We find only a small variation in this product across the samples. The GaInNAsSb structure has a low radiative recombination current due in part to its low photon energy and also to differences in conduction and valence band densities of states and less inhomogeneous broadening relative to GaInNAs. We speculate that Sb brings benefits as a surfactant producing more homogeneous wells so Sb may also be beneficial in structures at shorter wavelength. However, there is a large nonradiative current in GaInNAsSb and achieving further reductions in the non-radiative current is the major challenge in taking advantage of the good gain potential of this system.

We have shown experimentally that in GaInNAsSb/GaAs quantum-well lasers there are significant nonradiative contributions to threshold current from the barriers and the well. By matching a simulation to the experiment we find that Auger recombination in the barriers is very weak, due to the low carrier density. Shockley–Read–Hall recombination is the dominant source of nonradiative current, with the barriers making the major contribution, possibly due to their higher defect density than the wells. This suggests that significant improvements could be made by optimizing growth conditions and layer design, with particular attention to the barrier.