2O Ratio Research Articles

Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags

Accelerated carbonation is induced in pastes and mortars produced from alkali silicate-activated granulated blast furnace slag (GBFS)–metakaolin (MK) blends, by exposure to CO 2-rich gas atmospheres. Uncarbonated specimens show compressive strengths of up to 63 MPa after 28 days of curing when GBFS is used as the sole binder, and this decreases by 40–50% upon complete carbonation. The final strength of carbonated samples is largely independent of the extent of metakaolin incorporation up to 20%. Increasing the metakaolin content of the binder leads to a reduction in mechanical strength, more rapid carbonation, and an increase in capillary sorptivity. A higher susceptibility to carbonation is identified when activation is carried out with a lower solution modulus (SiO 2/Na 2O ratio) in metakaolin-free samples, but this trend is reversed when metakaolin is added due to the formation of secondary aluminosilicate phases. High-energy synchrotron X-ray diffractometry of uncarbonated paste samples shows that the main reaction products in alkali-activated GBFS/MK blends are C–S–H gels, and aluminosilicates with a zeolitic (gismondine) structure. The main crystalline carbonation products are calcite in all samples and trona only in samples containing no metakaolin, with carbonation taking place in the C–S–H gels of all samples, and involving the free Na + present in the pore solution of the metakaolin-free samples. Samples containing metakaolin do not appear to have the same availability of Na + for carbonation, indicating that this is more effectively bound in the presence of a secondary aluminosilicate gel phase. It is clear that claims of exceptional carbonation resistance in alkali-activated binders are not universally true, but by developing a fuller mechanistic understanding of this process, it will certainly be possible to improve performance in this area.

Influence of fertilisation and harvest time on fuel quality of giant reed ( Arundo donax L.) in central Italy

The perennial grass giant reed ( Arundo donax L.) has been proposed as a promising biomass energy crop in southern Europe. The aim of this study was to investigate the effects of two fertilisation levels (F = 200–80–200 N–P–K kg ha −1; UF = 0–0–0 N–P–K kg ha −1) and two harvest times (A: autumn, W: winter) on the biomass quality of giant reed as a solid fuel for combustion. Different aged crops grown in central Italy (latitude 43°40′N, and longitude10°19′E) in the period of 1996–2005 were collected and analysed. Our results confirmed that giant reed biomass is characterized by a high content of ash and silicon. Giant reed showed an increase in ash content from F to UF and from A to W. The production of biomass from fertilised crops harvested in the autumn may thus be a good method for reducing the ash content by about 20%. The results also showed an improvement in biomass combustion quality in 10-year-old crops due to a lower ash content and higher SiO 2/K 2O and CaO/K 2O ratios, which could contribute to a lower slagging tendency. This research should help to improve our knowledge of the chemical composition of giant reed and presents possible agronomic strategies to combine a high biomass yield with good combustion quality.

Multi-dimensional modeling of non-catalytic partial oxidation of natural gas in a high pressure reformer

A three-dimensional simulation model for non-catalytic partial oxidation of natural gas in a high pressure reformer has been developed. In the model, the numerical methods and submodels conventionally used in turbulent reacting flows are used. The GRI-Mech 3.0 mechanism and a tabulated chemistry approach are applied to model the non-catalytic oxidation of natural gases under high pressures and temperatures. The reactions are assumed to be fast, hence only the equilibrium states of the multi-step reactions are read in an off-line generated chemistry table. This chemistry table has been created using the equilibrium solver EQUIL from the CHEMKIN II package, and the equilibrium values are functions of the initial mixture compositions and the temperatures at a constant pressure. A presumed PDF model is applied to simulate the interactions between turbulent mixing and the multi-step chemical reactions. Simulations have been performed for a commercial natural gas reformer at various O 2/CH 4 and O 2/H 2O ratios and pressures in order to investigate the effect of these parameters on the syngas yields. The results have provided some insights into the strategies of solving the hot-spot problem in industrial reformers.

Assessment of phase formation in alkali activated low and high calcium fly ashes in building materials

The alkali activation of one low calcium hard coal fly ash and four high calcium lignite coal fly ashes was studied by means of conduction calorimetry, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy to assess their potential for mortar and concrete production. The ashes were activated by different additions of sodium silicate with a molar SiO 2/Na 2O ratio of 1.0. Besides the chemical analysis of the hydrated samples, strength tests have been carried out on mortars, applying different curing regimes. The results indicate that a high content of vitreous phase and low calcium content are important factors determining the reactivity and performance of fly ashes in alkali activated systems. In the high calcium fly ashes, less alkali aluminate silicate hydrates and a much more porous microstructure are formed compared to the low calcium fly ash. Consequently, the low calcium fly ash seems to be suited best for the production of building materials.

Structural investigation and electron paramagnetic resonance of vanadyl doped alkali niobium borate glasses

Glasses with compositions xNb 2O 5·(30 − x)M 2O·69B 2O 3 (where M = Li, Na, K; x = 0, 4, 8 mol%) doped with 1 mol% V 2O 5 have been prepared using normal melt quench technique. The IR transmission spectra of the glasses have been studied over the range 400–4000 cm −1. The changes caused by the addition of Nb 2O 5 on the structure of these glasses have been reported. The electron paramagnetic resonance spectra of VO 2+ ions in these glasses have been recorded in X-band (9.14 GHz) at room temperature (300 K). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V 4+ ions which exist as VO 2+ ions in octahedral coordination with a tetragonal compression in the present glasses. The tetragonality of V 4+O 6 complex decreases with increasing concentration of Nb 2O 5. The 3d xy orbit contracts with increase in Nb 2O 5:M 2O ratio. Values of the theoretical optical basicity, Λ th, have also been reported.

Discrimination and origin of the sanukitoid series: Geochemical constraints from the Neoarchean western Karelian Province (Finland)

Neoarchean late to post-tectonic sanukitoid intrusions are found in the western part of the Karelian Province in Finland. Variable-sized, even-grained to K-feldspar porphyritic intrusions form a series of diorites, tonalites, and granodiorites, that are calc-alkaline to alkali-calcic, magnesian, and mostly peraluminous. The major and trace element geochemistry of the intrusions show typical sanukitoid affinities: a mantle signature (high content of Mg, Ni, Cr and high Mg#) and enrichment in LILE (especially K, Ba, and Sr). The intrusions form a distinctive series that can be distinguished from the TTG series of the Karelian Province by their high Ba–Sr signature, low Na 2O/K 2O ratio, and uniform HREE pattern. The sanukitoid series can be compositionally constrained as follows: SiO 2 = 55–70 wt.%, Na 2O/K 2O = 0.5–3, MgO = 1.5–9 wt.%, Mg# = 45–65, K 2O = 1.5–5.0 wt.%, Ba + Sr > 1400 ppm, and (Gd/Er) N = 2–6. The probable source was enriched subcontinental lithosphere mantle with high LILE concentrations in phlogopite and/or sanidine. The accumulation of K, Ba, and Sr in the mantle source may have occurred as a consequence of two separate metasomatic events: 1) by subduction-related fluids/melts and 2) by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff. The slab breakoff at the end-stage of subduction is also a viable trigger for the sanukitoid magmatism.

Denitrification and total nitrogen gas production from forest soils of Eastern China

Reactive forms of nitrogen (Nr) are accumulating at local, regional and global levels largely due to human activities, particularly N-fertilizer production and use as well as fossil fuel combustion. This has resulted in a change in the nitrogen (N) cycle and excess Nr in the environment, which has negative environmental effects. Therefore, characterizing denitrification and the edaphic variables controlling denitrification and its products is the first step in predicting the long-term effects of Nr accumulation. In the present study, six forest soil types in different climatic zones were collected from East China and evaluated for denitrification products following a K 15NO 3 amendment and subsequent incubation. The results showed that denitrification, indicated by production of nitric oxide (NO), nitrous oxide (N 2O) and dinitrogen (N 2), was higher in the studied temperate forest soils than in the studied subtropical and tropical forest soils and was negatively correlated with soil redox potential at the beginning of incubation ( r = −0.94, P < 0.01), but not with soil pH. The ratios of NO/total N gas and N 2O/total N gas produced during denitrification varied among the soils, and were generally higher in the subtropical and tropical soils. Spearman's correlation analysis showed that the NO ratio was positively correlated with soil oxidation capacity (OXC) ( r = 0.94, P < 0.01) and redox potential at the beginning of incubation ( r = 0.86, P < 0.05), but negatively correlated with soil pH ( r = −0.83, P < 0.05). The N 2O ratio was not significantly correlated with these edaphic variables, but showed a significant correlation to NO ratio ( r = 0.83, P < 0.05). These results suggested that the OXC value might be the key factor affecting denitrification rates in soils. One possible explanation for these effects is that large OXC values would result in a higher level soil redox potential, thus suppressing denitrification and enhancing NO and N 2O ratios during denitrification.

Transdermal behaviour of the N-alkylamide spilanthol (affinin) from Spilanthes acmella (Compositae) extracts

Aim of the study N-Alkylamides are a large group of bioactive molecules found in several plants from the genera Echinacea, Xanthoxylum and Spilanthes. Extracts and formulations derived from these plants are not only orally used, but also applied on the skin as well. However, there is currently no specific information available about the intrinsic local pharmacokinetics of N-alkylamides after topical application on human skin, questioning the role of this mode of administration. The present study investigates the transdermal behaviour of spilanthol, a prominent N-alkylamide. Materials and methods Two pharmaceutically accepted dose solutions (ethanol and propylene glycol based aqueous donor vehicles), combined with three different receptor fluids (PBS, PBS + 0.5% HPβCD, EtOH/H 2O (30:70, v/v)), were applied on split-thickness human skin in a Franz diffusion cell (FDC) system. Fundamental permeation characteristics of spilanthol in a solvent-independent way (100% aqueous dose solution) were also obtained using an extrapolation approach with different organic solvent/H 2O ratios. Results and conclusions We demonstrated for the first time that spilanthol permeates the skin. The following aqueous-extrapolated primary transdermal parameters were obtained (mean ± SEM): K p,aq = 3.31 (±0.29) × 10 −3 cm/h, D m,aq = 1.86 (±0.09) × 10 −4 cm 2/h and K m,aq = 7.28 (±1.59) × 10 −1. Partitioning ( K m) was strongly dependent on the donor solution composition, while diffusion ( D m) was mainly influenced by the receptor fluid composition.

CO 2-rich komatiitic melt inclusions in Cr-spinels within beach sand from Gorgona Island, Colombia

The volatile content of komatiite is a key to constrain the thermal and chemical evolution of the deep Earth. We report the volatile contents with major and trace element compositions of ~ 80 melt inclusions in chromian spinels (Cr-spinels) from beach sands on Gorgona Island, Colombia. Gorgona Island is a ~ 90 Ma volcanic island, where picrites and the youngest komatiites known on the Earth are present. Melt inclusions are classified into three types on the basis of their host Cr-spinel compositions: low Ti (P type), high Ti with high Cr # (K1 type) and high Ti with low Cr # (K2 type). Chemical variations of melt inclusions in the Cr-spinels cover all of the island's lava types. P-type inclusions mainly occur in the picrites, K1-type in high-TiO 2 komatiites (some enriched basalts: E-basalts) and K2-type in low-TiO 2 komatiites. The H 2O and CO 2 contents of melt inclusions within Cr-spinels from the beach sand are highly variable (H 2O: 0.03–0.9 wt.%; CO 2: 40–4000 ppm). Evaluation of volatile content is not entirely successful because of compositional alterations of the original melt by degassing, seawater/brine assimilation and post-entrapment modification of certain elements and volatiles. However, the occurrence of many melt inclusions with low H 2O/K 2O ratios indicates that H 2O/K 2O of Gorgona komatiite is not much different from that of modern mid-oceanic ridge basalt (MORB) or oceanic island basalt. Trend of CO 2/Nb and Zr/Y ratios, accounted for by two-component mixing between the least degassed primary komatiite and low-CO 2/Nb evolved basalt, allow us to estimate a primary CO 2/Nb ratio of 4000 ± 2200 or a CO 2 content of 0.16 ± 0.09 wt.%. The determined CO 2/Nb ratio is unusually high, compared to that of MORB (530). Although the presence of CO 2 in the Gorgona komatiite does not affect the magma generation temperature, CO 2 degassing may have contributed to the eruption of high-density magmas. High CO 2/Nb and the relatively anhydrous nature of Gorgona komatiite provide possible resolution to one aspect of the hydrous komatiite debate.

Destruction of trichloroethylene during hydration of calcium oxide

Quicklime (calcium oxide, CaO) is often used as part of soil cleanup operations to remove contaminants or to create more favorable physical soil conditions for treatment. The extent to which quicklime chemically reacts with trichloroethylene (TCE) was evaluated by reacting CaO with a TCE–water mixture in test vessels designed to minimize volatilization loss. The impact of excess water and the presence of air were evaluated. During the hydration of CaO, a fraction of the spiked TCE was destroyed, and several different byproducts were detected (chloride and several organic chemicals). The primary organic byproduct was dichloroacetylene (DCA). In the presence of air, the degradation of DCA resulted in the formation of perchloroethylene (PCE), hexachloro-1,3-butadiene (HCDE), and chloroacetylene (CA). The maximum amount of TCE degradation occurred with a CaO/H 2O ratio of 1:1 in the presence of air. The formation of DCA was hindered by the presence of excess water. In the presence of excess water (a CaO/H 2O ratio of 1:2) the detected byproducts accounted for less than 4% of the total chlorine originally spiked as TCE.

Energy balance of the Deep Impact experiment

We present results on the energy balance of the Deep Impact experiment based on analysis of 180 infrared spectra of the ejecta obtained by the Deep Impact spacecraft. We derive an output energy of 16.5 (+9.1/−4.1) GJ. With an input energy of 19.7 GJ, the error bars are large enough so that there may or may not be a balance between the kinetic energy of the impact and that of outflowing materials. Although possible, no other source of energy other than the impactor or the Sun is needed to explain the observations. Most of the energy (85%) goes into the hot plume in the first few seconds, which only represents a very small fraction (<0.01%) of the total ejected mass. The hot plume contains 190 (+263/−71) kg of H 2O, 1.6 ± 0.5 kg of CO 2, 8.2 (+11.3/3.1) kg of CO (assuming a CO/H 2O ratio of 4.3%), 27.9 (+25.0/−8.9) kg of organic material and 255 ± 128 kg of dust, while the ejecta contains ∼10 7 kg of materials. About 12% of the energy goes into the ejecta (mostly water) and 3% to destroy the impactor. Volatiles species other than H 2O (CO 2, CO or organic molecules) contribute to <7% of the energy balance. In terms of physical processes, 68% of the energy is used to accelerate grains (kinetic energy), 16% to heat them, 6% to sublimate or melt them and 10% (upper limit) to break and compress dust and/or water ice aggregates into small micron size particles. For the hot plume, we derive a dust/H 2O ratio of 1.3 (+1.9/−1.0), a CO 2/H 2O ratio of 0.008 (+0.009/−0.006), an organics/H 2O ratio of 0.15 (+0.29/−0.11) and an organics/dust ratio of 0.11 (+0.30/−0.07). This composition refers to the impact site and is different from that of the bulk nucleus, consistent with the idea of layers of different composition in the nucleus sub-surface. Our results emphasize the importance of laboratory impact experiments to understand the physical processes involved at such a large scale.

Optimizing preparation of the TiO 2 thin film reactor using the Taguchi method

In this study, titanium dioxide thin film was prepared using the modified chemical vapor deposition. The parameters employed to control the preparation of the catalyst include the temperature of water bath, the Ti(OC 3H 7) 4/H 2O ratio, the flow rate of carrier gas, the oxidation temperature, the oxidation time, the calcination temperature, the rotating speed of furnace, and the speed of geared motor. The orthogonal arrays in the design of experimental method proposed by Taguchi were adopted to conduct the multiple-factor experiment. The conversion rate of salicylic acid in the aqueous or heterogeneous phase photocatalysis experiment was employed to identify the optimal conditions for assembly. The results indicated that a higher conversion ratio of the organic substance could be achieved under catalytic oxidation temperature of 400 °C, calcination temperature of 550 °C, and spraying speed of 30 rpm and the optimal experimental conditions obtained in this study were irradiation with intensity of 2.9 mW cm −2 on salicylic acid at concentration of 250 mg L −1 by both agitation and aeration processes (dissolved oxygen level = 8.2 mg O 2 L −1) at pH 5, which could achieve optimal hydroxyl radical yield of 5.1 × 10 −17 M.

WGS reaction over nanostructured CuO–CeO 2 catalysts prepared by hard template method: Characterization, activity and deactivation

This study focuses on water–gas shift reaction (WGSR) activity of CuO–CeO 2 catalysts containing 10, 15 and 20 mol% CuO synthesized by hard template method with KIT-6 silica acting as a template. The obtained solids were characterized by N 2 adsorption/desorption, XRD, H 2-TPR/TPD, N 2O decomposition, in situ DRIFTS and NH 3 chemisorption/TPD methods. The catalysts exhibited ordered mesoporous structure, which was identified as the negative replica of KIT-6 silica pore system with CuO dispersion values between 28 and 40%. H 2-TPR/TPD experiments revealed facile and extensive CeO 2 reduction in tested samples, which increased with CuO loading, indicating strong interactions between both oxide phases. On the other hand, abundance of surface acidic sites decreased with increasing CuO content. WGS reaction activity was tested at the stoichiometric CO/H 2O ratio and low contact times in the temperature range from 250 to 450 °C. At reaction temperatures above 375 °C, catalyst deactivation was observed, regardless of CuO content. Despite rigorous reaction conditions, CO conversion up to 62% was attained, with H 2 selectivity above 99% in the entire temperature range.

31P NMR spectroscopic studies of the influence of the environment in the degradation process of the Graham's salt

The “Graham's salt” is a vitreous sodium polyphosphate with a general formula of Na(n+2)PnO(3n+1). It is used in the ceramics industry as a deflocculant additive in a matrix of sodium silicate with different SiO2:Na2O ratios. The influence of the environment in which the Graham's salt is usually placed on its degradation into smaller particles has been studied by 31P NMR spectroscopy at several temperatures on solutions with 7% of Graham's salt in sodium silicate with Rw=1.6, 2.0, 3.3, in sodium carbonate 0.15M, in sodium hydroxide 0.10M and 1.0M and in water. The signals in the 31P NMR spectra of Graham's salt in D2O, depending on their chemical shift δ (ppm) and multiplicity, have been assigned to the different phosphorous atoms of the skeleton of the several polyphosphates that are present in the solution. The integration of these signals at different temperatures has enabled the collection of kinetic and thermodynamic data: kinetic constants k (s−1), activation energy Ea, ΔH‡ and ΔS‡. Results indicate that the environment is a factor which favours the degradation of polyphosphates, since with increasing basicity of deflocculating solutions the rate of degradation is faster. White gel obtained as a final product of the degradation process of Graham's salt has been analyzed with 31P NMR spectroscopic measurements identifying orthophosphate and pyrophosphate as the main final species of the degradation of Graham's salt.

Further evidences of deep convective vertical transport of water vapor through the tropopause

A few years ago, we identified a deep convective transport mechanism, of water vapor through the tropopause, namely, storm top gravity wave breaking, such that tropospheric water substance can be injected into the lower stratosphere via this pathway. The main evidence presented previously was taken from the lower resolution AVHRR images of the storm anvil top cirrus plumes obtained by polar orbiting satellites. Recent observations have provided further supporting evidence for this important cross-tropopause transport mechanism. There are now many higher resolution satellite images, mainly from MODIS instrument, that show more definitely the existence of these plumes, many of which would probably be unseen by lower resolution images. Furthermore, a thunderstorm movie taken in Denver (USA) area during STEPS2000 field campaign and another thunderstorm movie taken by a building top webcam in Zurich also demonstrate that the jumping cirrus phenomenon, first identified by T. Fujita in 1980s, may be quite common in active thunderstorm cells, quite contrary to previous belief that it is rare. We have used a cloud model to demonstrate that the jumping cirrus is exactly the gravity wave breaking phenomenon that transports water vapor through the tropopause. These additional evidences provide increasing support that deep convection contributes substantially to the troposphere-to-stratosphere transport of water substance. This corroborates well with recent studies of the stratospheric HDO/H 2O ratio which is much highly than it would be if the transport is via slow ascent. The only explanation that can be used to interpret this observation at present is that water substance is transported through the tropopause via rapid vertical motion, i.e., deep convection.

Why the atmosphere became oxygenated: A proposal

The increase in the oxidation state of the atmosphere during Earth history is well documented, but not the reasons for this process. The course of atmospheric evolution has been dominated by the effects of photosynthesis and by the composition of volcanic gases. The H 2/H 2O ratio of volcanic gases has remained essentially constant during most of Earth history. It is here proposed that their CO 2/H 2O and SO 2/H 2O ratios have increased with time. A simple model for the degassing and the recycling of CO 2, SO 2, and H 2O can account for many of the major steps in the oxygenation of the atmosphere.

Hydrogen-isotope systematics in degassing basaltic magma and application to Indonesian arc basalts

We have developed a predictive model for hydrogen-isotope shifts during degassing of basaltic–andesitic magma that takes the variation of water species with water content and temperature into account. OH⁎ (water dissolved as hydroxyl) is the dominant dissolved water species for the range of naturally observed magmatic water contents (0–8 wt.%) and temperatures (>800 °C), and increases in importance with higher temperatures and lower water contents. We used our hydrogen fractionation model and published experimental data to derive values for hydrogen-isotope fractionation factors between melt and H 2O vapor of 10 3 ln α OH⁎ = 34.9 + 16.7 × 10 6/ T 2 for OH⁎ and 10 3 ln α H 2O ⁎ = − 30.3 + 16.7 × 10 6/ T 2 for H 2O⁎ (water dissolved as molecular water). A value of zero for the latter, as was assumed in some recent and earlier studies, is incompatible with our model results. As a consequence of the progressively increasing OH⁎/H 2O⁎ ratio in the melt during degassing, the bulk hydrogen fractionation factor also increases continuously. In contrast, the influence of temperature on the bulk fractionation factor ΔD vapor–melt is relatively small. We applied the hydrogen fractionation model to thirty subaerial lavas of basaltic composition from eight volcanoes located in the Indonesian arc system. All samples are extensively degassed, as average contents of residual water in the melt are only ∼ 0.15 wt.%. Whole-rock δD values range from − 109‰ to − 57‰ VSMOW (average = − 89‰). Oxygen isotope compositions of the same samples range from + 5.3‰ to + 6.7‰ VSMOW and are close to MORB values, indicating that crustal contamination or post-eruptive weathering was insignificant. Hydrogen isotopes fractionated markedly during degassing, and our data agree best with dominantly closed-system exsolution of magmatic water during magma ascent and storage, followed by syn-eruptive open-system degassing from depths of less than a few hundred meters. Magmatic water was derived from a mantle source with a typical D-enriched arc isotopic signature. Within-suite systematics suggest variations in initial δD and δ 18O values for some volcanic centers.

A pseudo adakite derived from partial melting of tonalitic to granodioritic crust, Kyushu, southwest Japan arc

Cretaceous peraluminous granitic intrusions occur in Kyushu in the southwest Japan arc as batholiths or stocks accompanied by metaluminous tonalite to granodiorite. The peraluminous intrusions are classed as adakitic based on Sr/Y–Y (ppm) relationships, but they contain abundant K-feldspar, a phase not common in typical adakites. To consider their significance in the arc system, we investigated the Tsutsugatake stock as representative of the intrusions exposed in central Kyushu. The Tsutsugatake rocks are mainly garnet-bearing two-mica leuco-granitoids. Their Sr/Y ratios and rare earth element concentrations are appropriate for adakite, but K 2O/Na 2O ratios (0.53–1.43), and Al 2O 3 (13.7–15.0 wt.%), MgO (0.20–0.55 wt.%), Sr (207–462 ppm), Cr (≤ 12 ppm), and Ni (≤ 8 ppm) contents differ from those of typical adakite. Geochemical modeling shows that the petrogenesis of the Tsutsugatake stock can be explained by partial melting of arc-type tonalite or adakitic granodiorite under middle to lower crustal conditions, leaving amphibole and plagioclase as residual phases. The differences between the Tsutsugatake stock and classical adakites lie in their source rocks and melting conditions. The Tsutsugatake source was not basaltic, and the melting pressure was insufficient to stabilize garnet. The Tsutsugatake rocks are here designated “pseudo adakites”. Such “pseudo adakites” may be found in both modern and ancient arcs, and would play an important role in crustal evolution as a member of the recycled constituent.

Comparison of water–gas shift reaction activity and long-term stability of nanostructured CuO-CeO 2 catalysts prepared by hard template and co-precipitation methods

This study focuses on the characterization and water–gas shift reaction (WGSR) activity of CuO-CeO 2 catalysts containing 10, 15 and 20 mol% CuO synthesized by hard template method (HT) with KIT-6 silica acting as a template and co-precipitation method (CP). The obtained solids were characterized by SEM/TEM microscopy, N 2 adsorption/desorption, XRD, H 2-TPR/TPD, N 2O decomposition and NH 3 chemisorption/TPD methods. The preparation techniques yield fundamentally different products despite the same nominal chemical composition. Catalysts prepared by the HT method exhibited ordered mesoporous structure, which was identified as the negative replica of the KIT-6 silica pore system. Considerable differences in BET surface area (147–166 m 2/g for CuCe HT samples compared to 22–54 m 2/g for CuCe CP solids, respectively) were measured. CuO dispersion values between 28% and 40% were determined for CuCe HT solids, in case of CuCe CP samples, these values were in the range of 8–20%. H 2-TPR/TPD experiments revealed facile and extensive CeO 2 reduction in all tested samples, which increased with CuO loading. Very similar density of surface acidic sites was determined for both CuCe HT and CuCe CP catalyst samples at each CuO loading, with CuCe CP solids exhibiting the absence of strong acidic sites. WGS reaction activity was tested at the stoichiometric CO/H 2O ratio and low contact times in the temperature range from 250 to 450 °C. Despite rigorous reaction conditions, CO conversions up to 62% and 54% were attained for CuCe HT and CuCe CP samples, respectively, with H 2 selectivity above 99% over the entire temperature range. Superior BET surface area and CuO dispersion of CuCe HT samples are decisive factors contributing to higher activity in the investigated WGS reaction, compared to the ones synthesized by the co-precipitation method.

SIMULTANEOUS OBSERVATIONS OF COMET C/2002 T7 (LINEAR) WITH THE BERKELEY-ILLINOIS-MARYLAND ASSOCIATION AND OWENS VALLEY RADIO OBSERVATORY INTERFEROMETERS: HCN AND CH3OH

We present observations of HCN J = 1-0 and CH_3OH J(K_a, K_c) = 3(1, 3)-4(0, 4) A+ emission from comet C/2002 T7 (LINEAR) obtained simultaneously with the Owens Valley Radio Observatory (OVRO) and Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers. We combined the data from both arrays to increase the (u, v) sampling and signal to noise of the detected line emission. We also report the detection of CH_3OH J(K_a, K_c) = 8(0, 8)-7(1, 7) A^+ with OVRO data alone. Using a molecular excitation code that includes the effects of collisions with water and electrons, as well as pumping by the Solar infrared photons (for HCN alone), we find a production rate of HCN of 2.9 × 10^(26) s^(–1) and for CH_3OH of 2.2 × 10^(27) s^(–1). Compared to the adopted water production rate of 3 × 10^(29) s^(–1), this corresponds to an HCN/H_2O ratio of 0.1% and a CH_3OH/H_2O ratio of 0.7%. We critically assess the uncertainty of these values due to the noise (~10%), the uncertainties in the adopted comet model (~50%), and the uncertainties in the adopted collisional excitation rates (up to a factor of 2). Pumping by Solar infrared photons is found to be a minor effect for HCN, because our 15 synthesized beam is dominated by the region in the coma where collisions dominate. Since the uncertainties in the derived production rates are at least as large as one-third of the differences found between comets, we conclude that reliable collision rates and an accurate comet model are essential. Because the collisionally dominated region critically depends on the water production rate, using the same approximate method for different comets may introduce biases in the derived production rates. Multiline observations that directly constrain the molecular excitation provide much more reliable production rates.