Residence Time Of CO Research Articles

Mother adversity and co-residence time impact mother–child similarity in genome-wide and gene-specific methylation profiles

BackgroundThe effects of adverse life events on physical and psychological health, with DNA methylation (DNAm) as a critical underlying mechanism, have been extensively studied. However, the epigenetic resemblance between mother and child in the context of neglectful caregiving, and whether it may be shaped by the emotional impact of maternal stressful events and the duration of co-residence (indexed by child age), remains unknown. The present study examined mother–child similarity in methylation profiles, considering the potential effect of mother adversity, mother empathy, neglect-control group, child age (an index of years of mother–child co-residence), and mother age. Using Illumina Epic arrays, we quantified DNAm in 115 mother–child saliva samples. We obtained a methylation similarity index by computing correlation coefficients between methylation profiles within dyads, for the entire epigenome, and five specific genes related to stress and empathy: NR3C1, FKPB5, OXTR, SCL6A4, and BDNF.ResultsThe methylation profiles of the mother–child familial pairs significantly correlated as compared to mother–child random pairs for the entire epigenome and NR3C1, FKBP5, OXTR and BDNF genes. Next, multiple linear regression models observed associations of mother adversity, child age, and neglect-control group on mother–child methylation similarity, only significant in mother–child familial pairs, after correcting for multiple comparisons. Higher mother adversity was associated with lower mother–child methylation similarity for the epigenome-wide analysis, for the BDNF gene, and in the neglect-control group for the OXTR gene. In turn, being an older child (longer co-residence) was associated with higher mother–child methylation similarity.ConclusionsMother adversity and co-residence time are modulating factors in the intergenerational methylation process that offer a window into development-dependent adaptations that can be affected by both hereditary and environmental factors, significantly observed only in biological dyads. A twofold implication for child well-being emerges, one is positive in that children of mothers exposed to life adversity or neglect did not necessarily inherit their methylation patterns. The other is concerning due to the influence of time spent living together, which affects similarity with the mother and potentially increases the risk of inheriting an epigenetic profile associated with future dysfunctional parenting patterns. This underscores the importance of the 'the earlier, the better' recommendation by the Child Protection System, which is not always followed.

CO residence time modulates multi-carbon formation rates in a zero-gap Cu based CO2 electrolyzer

This study shows how flow field designs can be used to modulate CO concentrations and hydrocarbon production rates in a zero gap copper based carbon dioxide electrolyzer.

Hydrodynamics Change Tafel Slopes in Electrochemical CO2 Reduction on Copper

The hydrodynamics of electrochemical CO2 reduction (CO2R) systems is an insufficiently investigated area of research that has broad implications on catalyst activity and selectivity. While most previous reports are limited to laminar and CO2-sparged systems, herein we address a wide range of hydrodynamics via electrolyte recirculation systems. We find that increased hydrodynamics at the electrode surface results directly in changes to the ethylene and methane Tafel slopes, demonstrating that mass transport is on equal footing with catalyst active sites in determining reaction mechanisms and the ensuing product distribution. Mass transport is traditionally considered to be in the purview of systems-level engineering, yet the present work shows that CO2R mechanistic work must be considered in the context of the mass transport conditions. We extend our analysis to organic coatings, demonstrating that the films shield the active sites from variability in hydrodynamics and increase the residence time of CO so that it may be further reduced to desirable products.

Surface Hydroxyl Groups Enhance Ethylene Selectivity in Acidic CO2 Reduction Reaction

Acidic conditions can enable high single-pass conversion in electrochemical CO2 reduction (CO2R) reaction. However, the kinetically facile hydrogen evolution reaction (HER) prevails in acidic conditions and limits the energy efficiency for CO2R towards multi-carbon (C2+) products. By performing electrodeposition under CO2R conditions, we synthesized a copper catalyst (EC-Cu) that promotes selective CO2R to C2+ products in acidic conditions. We combine in situ spectroscopy, DFT calculations, and catalyst performance to show that co-adsorbed CO and OH on the catalyst surface promote C-C coupling, which we correlate with evidence of increased CO residence time. With optimization, the EC-Cu catalyst achieved a 60% faradaic efficiency for ethylene and 90% for C2+. Furthermore, when implemented in a slim flow cell, the EC-Cu catalyst can attain a 20% energy efficiency toward ethylene production.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Surface hydroxide promotes CO2 electrolysis to ethylene in acidic conditions

Performing CO2 reduction in acidic conditions enables high single-pass CO2 conversion efficiency. However, a faster kinetics of the hydrogen evolution reaction compared to CO2 reduction limits the selectivity toward multicarbon products. Prior studies have shown that adsorbed hydroxide on the Cu surface promotes CO2 reduction in neutral and alkaline conditions. We posited that limited adsorbed hydroxide species in acidic CO2 reduction could contribute to a low selectivity to multicarbon products. Here we report an electrodeposited Cu catalyst that suppresses hydrogen formation and promotes selective CO2 reduction in acidic conditions. Using in situ time-resolved Raman spectroscopy, we show that a high concentration of CO and OH on the catalyst surface promotes C-C coupling, a finding that we correlate with evidence of increased CO residence time. The optimized electrodeposited Cu catalyst achieves a 60% faradaic efficiency for ethylene and 90% for multicarbon products. When deployed in a slim flow cell, the catalyst attains a 20% energy efficiency to ethylene, and 30% to multicarbon products.

Cycling and status of cobalt in some forest types

Abstract The concentrations of Co were determined in the hydrological cycle (in maquis and fir forests), litterfall and soils in maquis, oak, beech and fir forests. The concentrations in the hydrological cycle were characterized by high variability. The concentrations in soil solution were much higher than those in the bulk deposition and throughfall. The contribution of the earth’s’ crust in the bulk deposition enrichment with Co was not high but some minor quantities of Co can be considered to be transported in long distances. The concentrations of Co in litterfall were high in the fraction composed of lichens, flowers and mosses, especially in the fir forest. The total content of Co was significantly higher in the soils derived from mica schist than those in the flysch. The residence time of Co in the forest floor was rather long. This is an indication that weathering in the mineral layers plays an important role in providing Co for plant uptake.

Highly selective and productive reduction of carbon dioxide to multicarbon products via in situ CO management using segmented tandem electrodes

Electrochemical CO2 reduction provides a promising route to the sustainable generation of valuable chemicals and fuels. Tandem catalysts enable sequential CO2-to-CO and CO-to-multicarbon (C2+) product conversions on complementary active sites, to produce high C2+ Faradaic efficiency (FE). Unfortunately, previous tandem catalysts exhibit poor management of CO intermediates, which diminishes C2+ FE. Here, we design segmented gas-diffusion electrodes (s-GDEs) in which a CO-selective catalyst layer (CL) segment at the inlet prolongs CO residence time in the subsequent C2+-selective segment, enhancing conversion. This phenomenon enables increases in both the CO utilization and C2+ current density for a Cu/Ag s-GDE compared to pure Cu, by increasing the *CO coverage within the Cu CL. Lastly, we develop a Cu/Fe-N-C s-GDE with 90% C2+ FE at C2+ partial current density (jC2+) exceeding 1 A cm−2. These results prove the importance of transport and establish design principles to improve C2+ FE and jC2+ in tandem CO2 reduction.

Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer-Tropsch Catalyst.

The way in which the triple bond in CO dissociates, a key reaction step in the Fischer–Tropsch (FT) reaction, is a subject of intense debate. Direct CO dissociation on a Co catalyst was probed by 12C16O/13C18O scrambling in the absence and presence of H2. The initial scrambling rate without H2 was significantly higher than the rate of CO consumption under CO hydrogenation conditions, which indicated that the surface contained sites sufficiently reactive to dissociate CO without the assistance of H atoms. Only a small fraction of the surface was involved in CO scrambling. The minor influence of CO scrambling and CO residence time on the partial pressure of H2 showed that CO dissociation was not affected by the presence of H2. The positive H2 reaction order was correlated to the fact that the hydrogenation of adsorbed C and O atoms was slower than CO dissociation. Temperature‐programmed in situ IR spectroscopy underpinned the conclusion that CO dissociation does not require H atoms.

Mesoporous alumina and alumina-titania supported KCuFe catalyst for Fischer-Tropsch synthesis: Effects of CO2 and CH4 present in syngas

In this work, mesoporous alumina (mAl2O3) and alumina-titania (mAl2O3-TiO2) were synthesized and used as support materials for promoted (K, Cu) iron catalyst. The catalysts were tested for Fischer-Tropsch synthesis in a fixed bed flow reactor operating at 2000h−1 GHSV, 270°C, 330psi and H2/CO ratio of 1.25. The catalytic activity was measured in terms of CO conversion, CO2 selectivity and hydrocarbon selectivity. The catalyst KCuFe/mAl2O3 performed better and showed ~17% higher CO conversion to hydrocarbons as compared to that shown by KCuFe/γ-Al2O3.The effect of CO2 and CH4 present in produced syngas (through gasification/reforming) and recycled syngas was also studied for KCuFe/mAl2O3 and KCuFe/mAl2O3-TiO2 catalyst. 0–15% of CO2 and 0–12.5% of CH4 was added in syngas, while maintaining GHSV constant. Methane in syngas acted as diluent and resulted in increase in CO residence time, which helps in increase in CO conversion. However, increase in CO conversion and decrease in partial pressure of CO leads to increase in CH4 and CO2 selectivity, thus, lowering the amount of percentage of CO converted to C5+ hydrocarbons. Addition of CO2 in syngas leads to decrease in CO2 selectivity, indicating hydrogenation of CO2 to hydrocarbons. Hence, slight increase in amount of percent CO converted to hydrocarbons was observed. Both catalysts showed increase in chain growth probability and alcohol production with increasing CH4 and CO2 content in syngas. However, the catalyst KCuFe/mAl2O3 performed better with CO2 and CH4 present in syngas, and has the potential to bring economic benefits to FTS process by relaxing the expensive syngas purification process for complete removal of CO2 and CH4.

Long-Term Energy and Climate Implications of Carbon Capture and Storage Deployment Strategies in the US Coal-Fired Electricity Fleet

To understand the long-term energy and climate implications of different implementation strategies for carbon capture and storage (CCS) in the US coal-fired electricity fleet, we integrate three analytical elements: scenario projection of energy supply systems, temporally explicit life cycle modeling, and time-dependent calculation of radiative forcing. Assuming continued large-scale use of coal for electricity generation, we find that aggressive implementation of CCS could reduce cumulative greenhouse gas emissions (CO(2), CH(4), and N(2)O) from the US coal-fired power fleet through 2100 by 37-58%. Cumulative radiative forcing through 2100 would be reduced by only 24-46%, due to the front-loaded time profile of the emissions and the long atmospheric residence time of CO(2). The efficiency of energy conversion and carbon capture technologies strongly affects the amount of primary energy used but has little effect on greenhouse gas emissions or radiative forcing. Delaying implementation of CCS deployment significantly increases long-term radiative forcing. This study highlights the time-dynamic nature of potential climate benefits and energy costs of different CCS deployment pathways and identifies opportunities and constraints of successful CCS implementation.

The efficiency of CO 2 sequestration via carbonate mineralization with simulated wastewaters of high salinity

Salinity generally strongly affects the solubility of carbon dioxide in aqueous solution. This would seem to involve a reduction of the efficiency of the carbonate mineralization process with the objective to sequester this greenhouse gas. On the contrary, we demonstrate here that with a more concentrated solution of magnesium chloride, the residence time of CO 2 is enhanced in the aqueous medium because of a reduced tendency to produce CO 2(g). Experiments intended to simulate more closely the Mg-rich wastewaters that are industrially available have been carried out using solutions differing in Mg concentration (7, 16, 32 g L −1 Mg). A comparison of the efficiency of the CO 2 mineralization process among sets of experiments shows that the reduction of the efficiency, to about 65%, was lower than that expected, as the low degree of CO 2 degassing results in the enhanced availability of carbonic ions to react with Mg ions to form stable carbonate minerals over a longer time.

Modeling the Woody Biomass Combustion in a Vortexing Fluidized-Bed Combustor

This study develops an isothermal one-dimensional model to easily predict the performance of biomass combustion in a vortexing fluidized-bed combustor (VFBC). This model comprises a series of three reactor zones: a fluidized-bed combustion chamber, a lower freeboard, and an upper freeboard. This model can calculate the composition of the flue gas exhausted from a combustor and the concentration profiles of individual gas species at various combustor heights. This study verifies the proposed model by comparing its predictions with actual experimental data obtained from a series of systematic combustion experiments burning pinewood sawdust in a pilot-scale VFBC. This comparison revealed an air-leakage problem in the pilot-scale VFBC. The simulated results of CO2 and O2 concentrations are most sensitive to EA but almost non-sensitive to λ. As for the operating temperature, the simulation results for CO, CO2, and O2 are only sensitive at temperatures lower than 750 °C. The CO concentration in the exhaust is more affected than CO2 and O2 by the secondary air added. The fresh O2 added by secondary air can enhance CO consumption, but too much secondary air shortens the residence time of CO in the upper freeboard. Although there are obvious gaps between experimental and simulation results, the predicted change tendencies of gas concentrations correspond to the actual data. This model makes it possible to obtain more information in the preliminary steps of designing a larger scale VFBC for burning highly volatile fuel, e.g., biomass.

The stability and transport of carbon dioxide on Iapetus

Carbon dioxide has been detected associated with Iapetus' dark material by the Cassini spacecraft. This CO 2 may be primordial and/or resulting from ongoing production by photolysis of water-ice in the presence of carbonaceous material [Allamandola, L.J., Sandford, S.A., Valero, G.J., 1988. Icarus 76, 225–252]. Although any primordial CO 2 would likely be complexed with the dark material and thus stable against thermal transport to Iapetus' poles [Buratti, B.J., and 28 colleagues, 2005. Astrophys. J. 622, L149–L152], active production of CO 2 would result in some fraction of the CO 2 being mobile enough to allow the accumulation of CO 2 at Iapetus' poles. We develop a computer model to simulate ballistic transport of CO 2 ice on Iapetus, accounting for Iapetus' gravitational binding energy and polar cold traps. We find that the residence time of CO 2 ice outside the polar regions is very short; a sheet of CO 2 ice near the equator of Iapetus decreases in thickness at a rate of 50 mm year −1. The sublimated CO 2 will ballistically move around Iapetus until it reaches the polar cold traps where it can be sequestered for up to 15 years. If the total surface inventory of CO 2 exceeds 3 × 10 7 kg , the polar ice cap will be permanent. While CO 2 is moving around the surface, a small percentage will eventually reach escape velocity and be lost from the system. As such, a seasonal polar cap is lost at rate of 12% every solar orbit as the CO 2 moves between the two polar cold traps.

Transient yielding of CO 2 over oxidized ruthenium surfaces: Monte Carlo simulations

We develop Monte Carlo simulations to study the catalytic oxidation of CO over a surface of ruthenium. The catalyst is exposed to a continuous flux of CO molecules and its surface is pre-covered with an amount of oxygen atoms. Recent experiments performed on this system [R. Blume, W. Christen, H. Niehus, J. Phys. Chem. B 110 (2006) 13912] have shown that three different reaction mechanisms can account for the experimental results. Two of them are based on the Langmuir–Hinshelwood mechanism, where CO molecules are adsorbed at oxygen-free defect sites before reactions take place. The third one proceeds via the Eley–Rideal mechanism, which is almost time independent, and reactions occur at non-defect sites. In our model, we consider a semi-infinite cubic lattice to mimic the surface of the catalyst and oxygen atoms are incorporated into the layers below the surface. A fraction of defects is created at the topmost layer and at the first subsurface layer. Oxygen atoms can diffuse over the surface as well as between adjacent layers of the system. We also assumed a temperature dependent reaction rate that is related to the residence time of CO at the surface. Comparisons are made between the CO 2 yielding at defect-rich and smooth surfaces as a function of temperature.

Efficient CO Oxidation at Low Temperature on Au(111)

The rate of CO oxidation to CO2 depends strongly on the reaction temperature and characteristics of the oxygen overlayer on Au(111). The factors that contribute to the temperature dependence in the oxidation rate are (1) the residence time of CO on the surface, (2) the island size containing Au-O complexes, and (3) the local properties, including the degree of order of the oxygen layer. Three different types of oxygen--defined as chemisorbed oxygen, a surface oxide, and a bulk oxide--are identified and shown to have different reactivity. The relative populations of the various oxygen species depend on the preparation temperature and the oxygen coverage. The highest rate of CO oxidation was observed for an initial oxygen coverage of 0.5 monolayers that was deposited at 200 K where the density of chemisorbed oxygen is maximized. The rate decreases when two-dimensional islands of the surface oxide are populated and further decreases when three-dimensional bulk gold oxide forms. Our results are significant for designing catalytic processes that use Au for CO oxidation, because they suggest that the most efficient oxidation of CO occurs at low temperature--even below room temperature--as long as oxygen could be adsorbed on the surface.

Technical and economic feasibility of CO 2 disposal in aquifers within the Alberta sedimentary basin, Canada

A three year study of the technical and economic feasibility of aquifer disposal of CO 2 in the low permeability sedimentary rocks of the Alberta Basin has revealed several new generic concepts that may be applicable to other sedimentary basins throughout the world. High permeability aquifers are not necessarily required for CO 2 disposal. Injectivity of CO 2 can be maximized by siting disposal wells in targeted or “sweet” zones of locally high permeability surrounded by a low regional scale permeability [1–2]. The low regional permeability forms a “hydrodynamic” or “time” trap for CO 2 [1], where the residence time of CO 2 in the aquifer is of the order of 10 5 to 10 6 years. Another type of hydrodynamic trapping in sedimentary basins is produced by the “sponge” or “sink” effect of rebounding shales [3–4]. On a smaller time scale, over hundreds of years, “mineral” or “inert” trapping [5–6] by reaction of the CO 2 with basic aluminosilicate minerals will occur in siliciclastic aquifers. Consequently, stratigraphic traps may not be necessary for safe disposal of CO 2 in the subsurface. Aquifer disposal of CO 2 is expensive, on the order of $52/tonne. Although there are many possibilities to reduce CO 2 emissions that are more economically attractive, aquifer disposal remains as one of the largest sinks available for CO 2 in landlocked areas of the world; and may be utilized if other less expensive options are exhausted.

Impact winter and the Cretaceous/Tertiary extinctions: Results of a Chicxulub asteroid impact model

The Chicxulub impact crater in Mexico is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary. 2-D hydrocode modeling of the impact, coupled with studies of the impact site geology, indicate that between 0.4 and 7.0 × 10 17 g of sulfur were vaporized by the impact into anhydrite target rocks. A small portion of the sulfur was released as SO 3 or SO 4, which converted rapidly into H 2SO 4 aerosol and fell as acid rain. A radiative transfer model, coupled with a model of coagulation indicates that the aerosol prolonged the initial blackout period caused by impact dust only if the aerosol contained impurities. A larger portion of sulfur was released as SO 2, which converted to aerosol slowly, due to the rate-limiting oxidation of SO 2. Our radiative transfer calculations, combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10–20% of normal for a period of 8–13 yr. This reduction produced a climate forcing (cooling) of −300 Wm −2, which far exceeded the +8 Wm −2 greenhouse warming, caused by the CO 2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures. Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO 2. The prolonged impact winter may have been a major cause of the K/T extinctions.

The reactivity of high oxygen coverages on Pd(110) in catalytic CO oxidation

The catalytic oxidation of CO on a Pd(110) surface has been investigated in CO titration experiments and under steady-state conditions in the 10 −4 Torr range. The reaction was followed by means of video-LEED, work function and rate measurements. The titration experiments with the oxygen-saturated Pd(110) surface revealed a change in the reaction mechanism from a uniform reduction of the oxygen coverage at high temperature ( T ≈ 500 K) to a hole-eating mechanism at low temperature ( T < 400 K). High oxygen coverages were found to have an inhibiting effect on the rate of CO 2 production. This effect, which presumably is associated with the formation of subsurface oxygen, can be attributed to a lowering of the CO residence time caused by a decrease in the adsorption energy of CO and to a reduction of the CO sticking coefficient. Under steady-state conditions this inhibiting effect leads to the appearance of a hysteresis in the high rate branch of the kinetics of catalytic CO oxidation upon cyclic variation of the CO pressure.

Homogeneous and heterogeneous CO chemical kinetics in liquid-nitrogen cooled 5% COHe discharges

The CO dissociation of a 5% COHe radiofrequency discharge has been analyzed as a function of CO residence time in discharge, in a reactor cooled at liquid-nitrogen temperature. The gas phase products (CO 2, O, C 2) as well as CO 2 trapped and carbonaceous film deposited on the cooled walls of the reactor, were analyzed by emission spectroscopy and mass spectrometry. The composition of carbonaceous deposit was found to be like C 2OC 3O 2, rather than C-like as generally assumed for COHe discharges. CO 2 and C 2OC 3O 2 formation yields increase with residence time, leading to CO loss up to about 80%, at a residence time of a few seconds. The first step of CO dissociation occurs mainly by electron impact, then the hetrogeneous reactions CO+O+wall→(CO 2) w and CO+C w→(C 2O) w effectively enhance the CO loss. In fact an autocatalytic CO dissociation, which arises by the sink of dissociation products on the reactor cooled walls has been measured. The high CO depletion in COHe mixture, as CO residence time is increasing, leads to an increase of electron mean energy which accelerates the electron impact CO dissociation.