The Effect of Copper Addition on the Activity and Stability of Iron-Based CO2 Hydrogenation Catalysts.

Iron-based CO2 catalysts have shown promise as a viable route to the production of olefins from CO2 and H2 gas. However, these catalysts can suffer from low conversion and high methane selectivity, as well as being particularly vulnerable to water produced during the reaction. In an effort to improve both the activity and durability of iron-based catalysts on an alumina support, copper (10-30%) has been added to the catalyst matrix. In this paper, the effects of copper addition on the catalyst activity and morphology are examined. The addition of 10% copper significantly increases the CO2 conversion, and decreases methane and carbon monoxide selectivity, without significantly altering the crystallinity and structure of the catalyst itself. The FeCu/K catalysts form an inverse spinel crystal phase that is independent of copper content and a metallic phase that increases in abundance with copper loading (>10% Cu). At higher loadings, copper separates from the iron oxide phase and produces metallic copper as shown by SEM-EDS. An addition of copper appears to increase the rate of the Fischer-Tropsch reaction step, as shown by modeling of the chemical kinetics and the inter- and intra-particle transport of mass and energy.

The role of stationary phase selection on performance for explosives analysis using GC-ECD.

Gas chromatography with electron capture detection (GC-ECD) analysis of explosive-related nitro organic compounds was performed using four different column stationary phases with the focus being on their impact on analyte stability and transfer efficiency during analysis. All four columns used were 6 m x 0.53 mm, and the four stationary phases were a 1.0-microm thick 5% phenyl siloxane/95% methyl siloxane non-polar phase, a 1.5-microm thick 5% phenyl siloxane/95% methyl siloxane non-polar phase optimized for explosives analysis, an intermediate polarity 0.5-microm thick trifluoropropylmethyl siloxane phase, and a proprietary intermediate polarity 0.5-microm thick phase. Although all exhibited similar recovery (as defined as the detector signal per injected mass) when new, the intermediate polarity phases maintained higher sample recovery over the course of analyzing hundreds of samples than the non-polar phases, particularly for the nitramines hexahydro-1,3,5-trinitro-1,3,5-triazine and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, for which a 7x and 3x decrease in recovery were observed, and the nitrate esters nitroglycerin and pentaerythritol tetranitrate, for which a 7x and 11x decrease in recovery were observed. For most other explosive-related compounds, the differences in recovery were between 1.5x and 3x over the same course. Although the detailed chemical formulation of the stationary phases have not been disclosed by their manufacturers, we attribute the observed differences in performance to the stability of their passivation chemistries with regard to other mobile-phase compounds contained in complex field samples. Although these effects have been qualitatively noted in the past and in response, maintenance procedures have been developed to help account for this behavior, the analyst's preference is to use an explosives analysis method that does not require these time-consuming measures. Our desire to prolong this maintenance interval provided the motivation for the assessment reported in this paper. From our assessment, we conclude that manufacturers of GC columns should focus more attention on the stationary phase and passivation chemistries that can lead to the development of a column that is better able to maintain passivation against explosive compound degradation; and users intending to perform large numbers of analyses using GC-ECD should make this a consideration when selecting a column.

Effects of pressure on the recovery of CO2 by phase transition from a seawater system by means of multilayer gas permeable membranes.

Using seawater doped with sodium bicarbonate and Celgard 2400 gas permeable membranes, bicarbonate ion disproportionates to carbon dioxide and carbonate when gaseous carbon dioxide is first removed from the seawater solution by diffusion through gas permeable membranes at elevated water pressures. The permeability of CO(2) by phase transition from bicarbonate solutions at pressures above 100 psi is only possible due to the use of multiple gas permeable membrane layers. The multiple layers minimize water permeability at pressures below and above the Young-Laplace bubble point of single membrane layers, however the gas permeability efficiency and rate are greatly decreased.

Measurement of trace explosive residues in a surrogate operational environment: implications for tactical use of chemical sensing in C-IED operations.

A campaign to measure the amount of trace explosive residues in an operational military environment was conducted on May 27-31, 2007, at the National Training Center at Fort Irwin, CA, USA. The objectives of this campaign were to develop the methods needed to collect and analyze samples from tactical military settings, to use the data obtained to determine what the trace explosive signatures suggest about the potential capabilities of chemical-based means to detect IEDs, and, finally, to present a framework whereby a sound understanding of the signature science can be used to guide development of new sensing technologies and sensor concepts of operation. Through our use of combined background and threat signature data, we have performed statistical analyses to estimate upper limits of notional sensor performance that is limited only by the spatial correlation of the signature chemicals to the threats of interest.

22-nm immersion interference lithography.

Immersion interference lithography was used to pattern gratings with 22-nm half pitch. This ultrahigh resolution was made possible by using 157-nm light, a sapphire coupling prism with index 2.09, and a 30-nm-thick immersion fluid with index 1.82. The thickness was controlled precisely by spin-casting the fluid rather than through mechanical means. The photoresist was a diluted version of a 193-nm material, which had a 157-nm index of 1.74. An analysis of the trade-off between fluid index, absorption coefficient, gap size and throughput indicated that, among the currently available materials, employing a high-index but absorbing fluid is preferable to using a highly transparent but low-index immersion media.

A variable-transmittance apodizing filter at 157 nm.

A variable-transmittance apodizing filter has been designed and demonstrated at 157 nm. The Gaussian transmission function is created by flowing oxygen gas, which is absorptive below 185 nm, between the two spherical surfaces of meniscus lenses. By varying the oxygen partial pressure, the degree of apodization can be controlled.