Production Of Carbon Oxides Research Articles

Research on Catalytic Reaction of Cotton Straw Pyrolysis Based on Model Compounds

The study starts from the clean conversion of desulfurized ash and biomass resources, based on correlation analysis and Langmuir-Hinshelwood model, studies the components of cotton stalk pyrolysis products and describes the mechanism and effects of desulfurized ash as a catalyst in the pyrolysis process. Regression analysis, support vector machine, and other methods are used to predict the yield or output of pyrolysis products, which is of great significance for the efficient utilization and sustainable development of cotton stalks. The study found that desulfurized ash significantly promoted the thermal decomposition of cotton stalks, increased the pyrolysis gas yield and lower heating value, increased the production of hydrogen-rich gas in the pyrolysis gas, and reduced the production of carbon oxides. Through the study of model compounds, it was found that desulfurized ash has different catalytic effects on the process of cellulose and lignin components in cotton stalks generating pyrolysis gas.

US power sector carbon capture and storage under the Inflation Reduction Act could be costly with limited or negative abatement potential

The United States’ (US) largest-ever investment in expected climate mitigation, through 2022’s Inflation Reduction Act (IRA), relies heavily on subsidies. One major subsidy, the 45Q tax credit for carbon oxide sequestration, incentivizes emitters to maximize production and sequestration of carbon oxides, not abatement. Under IRA’s 45Q changes, carbon capture and storage (CCS) is expected to be profitable for coal- and natural gas-based electricity generator owners, particularly regulated utilities that earn a guaranteed rate of return on capital expenditures, despite being costlier than zero-carbon resources like wind or solar. This analysis explores investment decisions driven by profitability rather than system cost minimization, particularly where investments enhance existing assets with an incumbent workforce, existing supplier relationships, and internal knowledge-base. This analysis introduces a model and investigates six scenarios for lifespan extension and capacity factor changes to show that US CCS fossil power sector retrofits could demand $0.4–$3.6 trillion in 45Q tax credits to alter greenhouse gas emissions by −24% ($0.4 trillion) to +82% ($3.6 trillion) versus business-as-usual for affected generators. Particularly given long lead times, limited experience, and the potential for CCS projects to crowd or defer more effective alternatives, regulators should be extremely cautious about power sector CCS proposals.

Extent of Inhibition of Malonic Acid on the Fermentation of Soursop Juice: A Thermodynamic Evaluation

The fermentation of soursop juice as substrate by Saccharomyces cerevisiae (yeast) was investigated to obtain certain useful thermodynamic parameters. This was achieved by the determination of the effects of temperature, substrate and inhibitor on the rate of carbon (IV) oxide (CO2) production. The extent of inhibition was examined by the addition of malonic acid inhibitor. The results indicate that the rate of fermentation of soursop juice increased in proportion with temperature (optimum 36oC), substrate (optimum 50%v/v) and malonic acid (optimum 30%v/v) up to a limit and decreased. This suggests that the reaction takes place in two steps (equilibrium and decomposition steps). The thermodynamic parameters determined are: enthalpy, ∆H* 151.14 kJmol-1; entropy of activation, ∆S* 275.359 Jmol-1k-1; Gibb’s free energy of activation, ∆G* -752.21 kJmol-1 and Equilibrium constant Keq, 1.33 respectively. The results show that the enthalpy value is positive indicating that the fermentation process is endothermic while the activation energy is same as the enthalpy. The entropy value is positive corroborating the positive enthalpy value. The fermentation process is spontaneous as shown by the negative change in free energy. These values were subsequently used to obtain by calculation Arrhenius constant A, 1.51x1023; orientation factor P, 1.41x10-34 and the collision frequency, Z, 1.07x1011 respectively. The calculated A and the P values obtained on the basis of collision theory and absolute reaction rate theory (or transition state theory), respectively show that the collision factor is of the order of 1011 min-1, about half that of gaseous molecules that can only be attained by an induced reduction in activation energy by a catalyst. The equilibrium constant value K suggests that the intermediate complex is rather interacting more with the substrate and also showing that only a limited amount of the substrate is converted to product. The equilibrium constant K is observed to be 1.33dm3mol-1 and not significantly far from unity implying that G* can be conveniently equated with the change in free energy at standard conditions. Finally, the type of inhibition was found to be uncompetitive from the extrapolated Lineweaver-Burk plots and did not bring about marked decrease in the rate of fermentation as expected.

Reactive force field (ReaxFF) molecular dynamics investigation of bituminous coal combustion under oxygen-deficient conditions

The microscopic reactive behaviours of functional groups in the Wiser bituminous coal model under burning of coal in atmospheres with various O2 concentrations were simulated by integrating molecular dynamics simulations with the reactive force field. The findings indicated that the combustion of coal molecules occurred through oxidation and cracking. The hydroxyl groups (OH) on coal were dehydrogenated, and additional free radicals then attacked the remaining oxygen atoms to form carbon oxides or water. The ether bond (O) was the most active functional group. Generally, the alkyl with the lowest molecular mass and on one side of the ether bond departs the functional group soon after the beginning of the simulation, and this was followed by the remaining oxygen atoms being attacked by free radicals to form carbon oxides or water. The carbonyl groups (CO) were the most stable functional group, they were attacked by O2 or ·O, resulting in the formation of carbon oxides in the second half of the simulation. In most cases, the hydrogen atom dissociated from the carboxyl group (COOH), generating CO2 from the remaining one carbon atom and two oxygen atoms. The concentration of O2 had a strong effect on the production of free radicals, carbon oxides, and water. Temperature had great effect on the breaking of chemical bonds and progress of chemical reactions. Free radicals ·OH, ·HO2, and C2O2 were important in coal combustion. Their numbers changed with temperature, affecting the way coal burned.

Corrosion Susceptibility of Mesoporous Carbons: Evidential Understanding of the Effects of Quasi-Passive Oxide Formation

Carbon is an essential component of catalyst layers in Proton Exchange Membrane Fuel Cells (PEMFCs), especially in cathodes, serving as a support material to disperse electrocatalysts. However, one of the challenges in the use of carbon in electrochemical applications is its propensity towards corrosion due to electrochemical oxidation at positive potentials, a crucial factor limiting device lifetime and thus large-scale commercialization. While most prior studies of carbon corrosion have focussed on microporous carbon powders, such as carbon black (e.g., Vulcan powder (VC)), CNTs, and graphite), there is a growing recognition of the need for larger pores in order to access the full internal surface area of carbon, especially at high currents.Here, we provide evidence from our own testing protocols focussed on sucrose-derived ordered mesoporous carbons (OMC-S) and other analogous carbons, that an oxide film with pseudo-passivating characteristics, forms on carbon surfaces once the potential is above that for oxygen evolution (E0 =1.23 V) in deaerated 0.5 M H2SO4. The conclusion builds on the observation of a never previously reported electrochemical feature in the first full cathodic scan after oxidation at higher potentials, with a cathodic plateau current that commences at 0.8 V, having a charge that is threefold higher than that of pseudocapacitive oxides, and is independent of sweep rate and solution agitation. Its steady current response upon reduction and other properties will be shown to be similar to what is seen for the reduction of a passive oxide film, as it is clearly shown to protect carbon at least partly from corrosion. We refer to this as a ‘quasi-passive oxide’ film, due to its electrochemical characteristics and its ability to prevent further carbon roughening. This oxide shares commonality with passive oxides commonly formed anodically on metals as well. We also show that due to its partially protective nature, more aggressive corrosion of the OMC-S occurs when this quasi-passive oxide is removed from the surface, presumably as fresh carbon surfaces are then available for corrosion. While more quasi-passive oxide can be reduced at potentials negative of 0 V vs RHE, the hydrogen evolution reaction is an interferent. We also discuss the effects of various electrochemical conditions, such as the upper potential used (E+) and the time of holding at E+ on quasi-passive oxide formation and its role in carbon corrosion susceptibility.While the formation of quinone-type passive oxide films has been evidenced based on carbon corrosion studies carried out by others, there have been no in-depth electrochemical studies that clearly distinguish the formation of various types of surface oxides or of CO2, or that correlate oxide formation with corrosion susceptibility, Therefore, our approach in this study presents significant insights that differentiate the carbon oxidation products, most importantly the irreversible oxidation of C to CO2 from the likely more harmless formation of a surface oxide. All analogous mesoporous carbons we investigated in this study are also found to form the quasi-passive oxide film at high potentials in acidic media, showing that this type of quasi-passive oxide film formation is a general phenomenon for carbons when subjected to at high potentials, albeit at varying rates due to surface area and porosity effects.

Thermogravimetric Oxidation Analyses of Carbon Tokamak Codeposits and Flakes

The erosion and redeposition of first-wall armor materials is a problem in nuclear fusion devices with carbon walls, where deuterium, tritium, and (eroded) carbon present in the plasma are deposited on the walls of the device, trapping the expensive and radiologically hazardous tritium. Thermo-oxidation, in which vessel surfaces are heated and oxygen containing gas is injected, is a possible solution. It results in the production of carbon oxides and tritiated water vapor, which can be pumped out by the vacuum pumps and recycled in a tritium recycling facility. In the present study, thermogravimetric analysis was used to measure the mass loss (or gain) of codeposited specimens from the General Atomics DIII-D National Fusion Facility under thermo-oxidation, in addition to laser thermal desorption spectroscopy. X-ray photo-electron spectroscopy was also used in this work to examine the tile’s surface composition pre and post oxidation. Dust scraped from the specimen was also studied, as this is a surrogate for dust that naturally falls from the tile codeposits and builds up in the tile gaps. One key conclusion is that boron oxides form where boron is present in the codeposit as an impurity, and these oxides dominate the weight-change behavior of the codeposit specimens for long exposures.

Facile Synthesis of Phosphorus and Cobalt Co-Doped Graphitic Carbon Nitride for Fire and Smoke Suppressions of Polylactide Composite.

Due to the unique two-dimensional structure and features of graphitic carbon nitride (g-C3N4), such as high thermal stability and superior catalytic property, it is considered to be a promising flame retardant nano-additive for polymers. Here, we reported a facile strategy to prepare cobalt/phosphorus co-doped graphitic carbon nitride (Co/P-C3N4) by a simple and scalable thermal decomposition method. The structure of Co/P-C3N4 was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The carbon atoms in g-C3N4 were most likely substituted by phosphorous atoms. The thermal stability of polylactide (PLA) composites was increased continuously with increasing the content of Co/P-C3N4. In contrast to the g-C3N4, the Polylactide (PLA) composites containing Co/P-C3N4 exhibited better flame retardant efficiency and smoke suppression. With the addition of 10 wt % Co/P-C3N4, the peak heat release rate (PHRR), carbon dioxide (CO2) production (PCO2P) and carbon oxide (CO) production (PCOP) values of PLA composites decreased by 22.4%, 16.2%, and 38.5%, respectively, compared to those of pure PLA, although the tensile strength of PLA composites had a slightly decrease. The char residues of Co/P-C3N4 composites had a more compact and continuous structure with few cracks. These improvements are ascribed to the physical barrier effect, as well as catalytic effects of Co/P-C3N4, which inhibit the rapid release of combustible gaseous products and suppression of toxic gases, i.e., CO.

Kinetic and reactor performance of a Ni-based catalyst during the production of ethene

ABSTRACTSteam cracking of diverse hydrocarbon sources is nowadays the main technology used to produce ethene worldwide, however, it presents energetic and environmental limitations related to the large consumption of energy and production of carbon oxides. To overcome this, industry and academy have aimed their research at developing a new technology based on the oxidative dehydrogenation (ODH) of ethane. Main challenges for its industrial implementation are yet catalyst and industrial reactor design. In this sense, Ni based catalysts have been promising materials for the production of ethene out of ethane at laboratory scale, however there is a scarce amount of researching on engineering aspects related to the evaluation of their performance at industrial scale. This work is aimed at giving insights on the performance of a Ni-loaded Y zeolite catalyst (Ni/KY) during the ethene production via ODH of ethane in an industrial-scale wall-cooled fixed bed catalytic reactor with a low dt/dp. To achieve this, an industrial reactor model that couples reaction kinetics to heat and mass transport phenomena is developed following reactor engineering fundamentals. To assess the kinetics of the ODH of ethane over the aforementioned catalyst, a detailed kinetic model is developed using published experiments [J. Catal. 265 (2009) 54–62]. Then, this kinetics is coupled to the industrial-scale reactor model, a 2D heterogeneous model accounting for heat and mass transport. The kinetic model following a Langmuir–Hinshelwood–Hougen–Watson mechanism allows an accurate description of laboratory data. Activation energy, related to the formation of ethene, and enthalpy adsorption of ethene indicate that the production ethene is favored at larger reaction temperatures, however, once it is produced, this olefin is more strongly adsorbed on the catalyst surface than the other byproducts. However, from the parametric sensitivity study applied to the industrial reactor, a larger coolant temperature brings out a significant but positive effect on the yield of ethene whereas a lower concentration of ethane in the feedstock favors the oxydehydrogenation reaction rather than total oxidation reactions. To this end, the proposed industrial reactor technology, along with the Ni/KY material, overcomes the hot spot formation and enables operations at larger temperatures, hence, favoring the production of ethene rather than carbon oxides.

A Comparative Study of Basic, Amphoteric, and Acidic Catalysts in the Oxidative Coupling of Methanol and Ethanol for Acrolein Production.

The impact of acid/base properties (determined by adsorption microcalorimetry) of various catalysts on the cross-aldolization of acetaldehyde and formaldehyde leading to acrolein was methodically studied in oxidizing conditions starting from a mixture of methanol and ethanol. The aldol condensation and further dehydration to acrolein were carried out on catalysts presenting various acid/base properties (MgO, Mg-Al oxides, Mg/SiO2 , NbP, and heteropolyanions on silica, HPA/SiO2 ). Thermodynamic calculations revealed that cross-aldolization is always favored compared with self-aldolization of acetaldehyde, which leads to crotonaldehyde formation. The presence of strong basic sites is shown to be necessary, but a too high amount drastically increases COx production. On strong acid sites, production of acrolein and carbon oxides (COx ) does not increase with temperature. The optimal catalyst for this process should be amphoteric with a balanced acid/base cooperation of medium strength sites and a small amount (<100 μmol g-1 ) of very strong basic sites (Qdiff >150 kJ mol-1 ).

Study of coal oxidation behaviour in re-opened sealed heating

Possible changes in the oxidation behaviour of coal in the spontaneous combustion site of re-opened sealed heating were studied. Two samples of bituminous coal and three types of coal pre-treatment procedures were applied to simulate in situ conditions at the “spon-com” site: i) pre-oxidation of coal, ii) pre-heating of coal under inert gas, and iii) immersion of pre-heated coal in liquid water. Pre-treated samples were then examined for the production rate of the indication gases evolved during oxidation and for oxidation heat effects. Two main conclusions were drawn with respect to oxidation of the coal in re-opened sealed heating: i) carbon monoxide and unsaturated hydrocarbons maintain their relevance as spontaneous combustion indication gases, however, increased production of both carbon oxides can be expected; ii) coal in the extinguished spontaneous combustion site gains increased susceptibility to the self-heating process.

COMPUTER SIMULATION OF THE PROPAGATION OF HEAT IN ABANDONED WORKINGS INSULATED WITH SLURRIES AND MINERAL SUBSTANCES

Abstract In the paper the results of investigations aimed at further identification of the phenomena occurring in abandoned workings and connected with the flow of air-gas (methane, carbon dioxide, nitrogen, oxygen and carbon oxidation products) mixture with taking into consideration the impact of supplied mineral substances on the processes of self-heating of the coal left in goaves were presented. The known and successfully used method for the prevention of fires in abandoned workings is the technology of filling goaf with an ash-air mixture, which also raises the issue of the effective use of that mixture. The computer, i.e. digital simulation methods being developed and intended for the purpose of the process discussed here are a good complement of the use of that technology. A developed mathematical model describing the process of additional sealing of gob with wet slurry supplied with three pipelines is based on the balance of volume of the supplied mixture and contained in the body created in goaves. The form of that body was assessed on the basis of the observation results available in literature and the results of model investigations. The calculation examples carried out for the the longwall area and its goaf ventilated with the “U” system allow to state that the introduced modification of the mathematical model describing the flow of the mixture of air, gases, and wet slurry with consideration of the coal burning process in the fire source area was verified positively. The digital prognostic simulations have confirmed a vital impact of the wet slurry supplied into the goaf on the processes of coal burning and also the change of rate and volume flow rate of the air mixture in goaf. As a complement to the above it should be noted that such elements as the place of the slurry supply in comparison with the longwall inclination or fire source area location is of great importance for the effectiveness of the fire prevention used. The development of computer/ digital simulation methods requires further investigations of the model adopted in this study. Those investigations should be aimed at making credible the theoretical model of the mixture flow through porous medium and the supplied mineral material. Such investigations will allow to verify the body form based on the mixture parameters such as humidity, viscosity, and fluidity and depending on the properties of the porous medium. Further development of the modelling of the phenomena discussed in this paper should be based on the methods of use of the description of the flow of fluids and slurry on the basis of 3D models.

Characteristics of pine wood oxidative pyrolysis: Degradation behavior, carbon oxide production and heat properties

Oxidative pyrolysis of pine wood was studied by thermogravimetric analysis (TGA) coupled with mass spectrometer (MS) and differential scanning calorimetry (DSC) methods. The effects of oxygen concentration on pyrolysis behavior, carbon oxide production and heat properties were investigated. Several parameters were defined to evaluate the oxygen influence. It was found that oxygen dramatically promotes the oxidative degradation and char oxidation rate. The reactivity index was found to be proportional to the oxygen concentration, which suggested that oxidative degradation reactions were under increasingly kinetic control in elevated oxygen concentration environments. Carbon oxides evolution properties were investigated. There are two releasing peaks in MS curves for oxidative condition comparing with one peak under inert condition. They are related with oxidative degradation and char oxidation, respectively. Both total amounts and rates of carbon oxides emission were found to increase with oxygen concentration. The cumulative emission ratio of CO to CO2 first decreases then increases with oxygen concentration with 10% as turning point. It may be caused by different oxygen diffusion behaviors with variable oxygen concentrations. The absolute reaction heat value of oxidative pyrolysis (−7.23MJkg−1, 5% O2) is much larger than that of inert condition (+0.28MJkg−1). Increasing of oxygen concentration results in an increase of heat emission. Comparing with pine wood low heat value, the net heat emission efficiencies under different oxygen concentrations (5%, 10%, 15%, 21%) are 39.73%, 44.84%, 68.90% and 78.41%, respectively.

Interrelation of anode and cathode processes in electrochemical carbon oxidation in a fuel cell with molten carbonate electrolyte

The object to be investigated is a fuel cell with a free molten carbonate electrolyte, which ensures direct electrochemical oxidation of solid hydrocarbons. The polarization characteristics of anode and cathode fuel cell assemblies, and also composition and gas release rate of gaseous products of anode reactions are studied. It is shown that the maximum voltages in the open cell circuit are obtained when the oxygen-carbon dioxide ratio in the cathode gas mixture corresponds to stoichiometric reaction coefficients that ensure replenishment of ions in electrolyte. However, the maximum current density values were obtained with a low carbon dioxide content. It is found that at high current values, anode potential fluctuations are observed. It is shown that carbon monoxide is the product of anode processes, along with carbon dioxide. The carbon monoxide content grows with temperature. The carbon dioxide content grows with increasing current in the fuel cell and with growing carbon dioxide content in cathode gases. The release rate of carbon oxidation products nonlinearly depends on the current value in the fuel cell. It is concluded that there is interrelation between the mass-exchange processes in the fuel cell, which is determined by the balance between cathode gas incoming into the reaction zone, the number of molecules generated during fuel oxidation, molecule dissolution and diffusion into the cathode region, and also the amount of gas released in the form of bubbles.

Thermal Degradation of Polyethylene Bags and Millet Stalks: Influence of the Temperature and the Local Concentration of Oxygen on the Conversion Rate of Carbon

This paper concerns the influence of temperature and local concentration of oxygen on the conversion efficiency of carbon into CO, CO2, CH4, C3H8, C2H4, C2H2, C2H6, C6H6, during the thermal degradation of plastic bags and millet stalks. The experimental device used is the tubular kiln, coupled to an analyzer Fourier Transform Infrared (FTIR) and a Non Dispersive Infrared analyzer (NDIR). Temperatures are considered between 800 and 1000°C. Local concentrations of oxygen during thermal degradation are 0%, 10% and 21%. On the one hand results obtained on the influence of temperature show that for each type of thermal degradation and whatever the temperature of the combustion, the rate of conversion of carbon remains substantially the same. In the case of plastic bags, the rate of carbon converted during pyrolysis is about 90% of carbon converted during reductive combustion. On the other hand, with millet stalks, the carbon converted represents only 60% of the rate of carbon converted during combustion to 10% oxygen. 1 to 2% of carbon not analyzed is in the form of aromatic compounds that are found most often in the soot and/or tar from this combustion system. Moreover, whatever the temperature, the overall efficiency of carbon conversion increases linearly with the local concentration of oxygen. During the thermal degradation of plastic bags, we see that the reducer environment has fostered the conversion of 7% of carbon more while the presence of oxygen in double proportion promotes the conversion of 27% carbon. Regarding the influence of the local content of oxygen, it is clear that for plastic bags, the reactions of oxidation of CO into CO2 tend to be favored for the benefit of those of hydrocarbons into CO. The formation of CO and CO2 by oxidation of light hydrocarbons is primarily from gaseous compounds CH4 and C2H4. At 950°C, we have also acetylene (C2H2) which is involved in the production of carbon oxides. At 1000°C, benzene (C6H6) heavily involved in the formation of CO and CO2. However, with millet stalks, more the local content of oxygen increases, more combustion is better, that is to say that the oxidation reactions producing CO2 are faster than the oxidation reactions of hydrocarbons into CO. The rate of carbon converted into CO and CO2 is higher for millet stalks than for plastic bags, due to this oxygen levels higher in millet stalks than in plastic bags. Similarly, for the millet stalks, from pyrolysis to combustion (at 10 and 21% oxygen), there is practically no hydrocarbon emitted.

Oxidative dehydrogenation of ethane over NiO–CeO 2 mixed oxides catalysts

In this paper we present the synthesis, characterization and catalytic behaviour in the oxidative dehydrogenation of ethane of NiO–CeO 2 mixed oxides. The addition of cerium oxide to NiO strongly modifies its catalytic performance, although the changes in the catalytic behaviour depend on the catalyst composition. The incorporation of low amounts of cerium oxide to NiO multiplies the productivity to ethylene in the oxidative dehydrogenation of ethane by a factor of ca. 7, which is the result of an increase in both catalytic activity and selectivity to ethylene. The enhanced activity has been related to the remarkable increase of the surface area of catalyst and the low crystal sizes of NiO that takes place when a tiny amount of cerium oxide is incorporated to the NiO. The higher selectivity to ethylene has been related to the modification of the nature of Ni–O species, which implies a lower production of carbon oxides. On the other hand, high activity and selectivity is also observed over catalysts rich in cerium (with Ni/Ce ratios between 0.2 and 3). In this case, a different mechanism can be proposed in which the high capacity of CeO 2 to bomb oxygen from bulk to surface and the partial formation of NiO and Ce 1− x Ni x O 2 facilitates a faster reoxidation of active Ni-sites by a synergic effect improving catalytic activity.

Lateral advection of organic matter in cascading-dominated submarine canyons

In the Gulf of Lions (GoL), dense water overflowing off the shelf occurs seasonally and represents the main mechanism affecting the shelf-slope exchange of particulate organic matter (OM). Most of the dense water export takes place in the south-western GoL and in particular through Cap de Creus (CdC) submarine canyon. Here, benthic instruments were deployed to collect down-canyon particulate fluxes whereas surface sediments were taken after the cascading event along the sediment dispersal system on the shelf, in CdC canyon and in the nearby Lacaze-Duthiers (LD) canyon. The chemical composition of the suspended material and surface sediments were investigated using several proxies including organic and inorganic carbon, total nitrogen, biogenic silica, δ 13C, Δ 14C, and alkaline CuO oxidation products. Thermohaline anomalies and high current speed events were measured in CdC canyon since December 2004 until mid-April 2005 indicating a marked off-shelf export of dense water trough the canyon. During the cascading, mud and relatively coarse shelf and upper canyon sediments were the major component of the mass flux. Conversely, advection of fine material via nepheloid layers dominated down-slope fluxes during pre- and post-cascading. The resulting change in grain-size affected the flux of mineral-bound terrigenous OC, indicating that the down-canyon transport of land-derived OM did not occur as bulk but rather its composition is driven by sediment sorting associated with different transport mechanisms. Both surface sediments and sediment trap samples indicated that CdC canyon is well connected to the GoL terrigenous dispersal system. Conversely, our results suggest an overall limited influence of land-derived OM in LD canyon. In spite of the reduced fluvial nutrient supply, a significant pulsed input of modern marine OM was observed in April 2005 at the end of the cascading period. Both intense mixing and lack of strong water column stratification likely played a key role allowing for both diffusion of nutrients-rich waters into the euphotic zone and efficient vertical sink of marine OC. On its way toward the seafloor, this fresh pool of OC interacted with the dense plume overflowing off the shelf, becoming part of the material laterally advected to the slope.

Semi-continuous hydrogen production from catalytic methane decomposition using a fluidized-bed reactor

Non-oxidative, catalytic decomposition of hydrocarbons is an alternative, one-step process to produce pure hydrogen with no production of carbon oxides or higher hydrocarbons. Carbon produced from the decomposition reaction, in the form of potentially valuable carbon nanotubes, remains anchored to the active catalyst sites in a fixed bed. To facilitate periodical removal of this carbon from the reactor and to make hydrogen production continuous, a fluidized-bed reactor was envisioned. The hypothesis that the tumbling and inter-particle collisions of bed material would efficiently separate nanotubes anchored to the active catalyst sites of the bed particles was tested and shown to be invalid. However, a switching mode reaction system for the semi-continuous production of hydrogen and carbon nanotubes by periodic removal and replenishment of the catalytic bed material has been successfully demonstrated.

Adrenocorticotropic Hormone/Cortisol Response to Physical Exercise in Abstinent Alcoholic Patients

Alterations in the hypothalamic-pituitary-adrenal (HPA) axis in alcoholic patients have been reported in various experimental conditions. To establish whether alcoholism affects the HPA axis activation during physical exercise, 10 recent abstinent alcoholic patients (age range: 33-45 years; duration of alcohol dependence: range 4-6 years) were tested by exercising on a bicycle ergometer. Ten age-matched healthy nonalcoholic men participated as controls. The workload was gradually increased at 3-minute intervals until exhaustion and lasted about 15 minutes for all subjects. Alcoholic patients were tested at 3 time points, at 4, 6, and 8 weeks after alcohol withdrawal, whereas controls were tested only once. Main outcome measurements were circulating levels of adrenocorticotropic hormone (ACTH) and cortisol and physiological variables during physical exercise [heart rate, blood pressure, ventilation, frequency of breathing, tidal volume, oxygen consumption (VO2), carbon oxide production (VCO2), and respiratory exchange ratio (R)]. Similar basal and exercise-induced changes in physiological variables were observed in controls and alcoholic patients in all tests. Basal levels of ACTH and cortisol were similar in all tests performed on alcoholic patients and on normal controls. In normal subjects, exercise induced a significant increase in plasma ACTH and serum cortisol levels, with peak levels at 20 minutes for ACTH (84% higher than baseline) and at 30 minutes for cortisol (70% higher than baseline). After 4 weeks of abstinence, slight but not significant ACTH/cortisol responses to physical exercise were observed in alcoholic patients (mean peaks were 10 and 18% higher than baseline, respectively, for ACTH and cortisol). By contrast, when the exercise test was repeated after 6 weeks abstinence, ACTH/cortisol levels rose significantly versus baseline (mean peak levels of ACTH and cortisol were 48 and 38% higher than baseline, respectively, for ACTH and cortisol). However, the hormonal responses were significantly lower than in the normal controls. At 8 weeks of abstinence, ACTH/cortisol responses were significantly higher than 2 weeks previously, and were not distinguishable from the increments observed in the normal controls (76 and 68% higher than baseline, respectively, for ACTH and cortisol). In concurrence with previous reports showing alterations of the HPA axis in the central nervous system in alcohol-dependent subjects, these data show a defect of the neuroendocrine mechanism(s) underlying the ACTH/cortisol response to physical exercise for at least a month after alcohol withdrawal, with reconstitution of a normal hormonal response at 8 weeks.

Electro-Oxidation of Concentrated Ce(III) at Carbon Felt Anode in Nitric Acid Media

Electro-oxidation of Ce(III) to Ce(IV) in parallel plate flow type electrolyzer divided with cation exchange membrane was carried out in nitric acid media at carbon felt anode under galvanostatic conditions. Carbon felt was used as an anode for its high specific surface area and high oxygen evolution overpotential. Pt coated Ti plates were used as cathode and anode current feeder. The oxidation of 1 mol·L −1 Ce(III) solution in 2 mol·L −1 HNO 3 was proceeding with a high current efficiency (92%) until about 80% of Ce(III) was oxidized. Then, oxygen evolution, accompanied by terminal voltage jump, took place, lowering current efficiency. Ce(III) was oxidized up to 90% with current efficiency of 62%. In this mode, strong carbon felt anode oxidation was observed. The wear out of carbon felt was 46% in six consequent runs (6 h of operation). After each run, carbon felt surface had to be renewed with slightly alkaline solution to remove carbon oxidation products and ensure regular operational conditions. When anode surface was blocked, oxygen evolution took place from the beginning of electrolysis due to higher actual current density. The wear out of carbon felt anode could be minimized by means of oxygen evolution prevention. In the case when electrolysis had been stopped before oxygen evolution started (at Ce(IV) conversion of about 80%), the wear out of anode was less than 2% during 6 consequent runs (4 h of operation).

Study of electrochemical instabilities of PEMFC electrodes in aqueous solution by means of membrane inlet mass spectrometry

Abstract Electrochemical stability of electrodes based on C and Pt/C materials is studied in aqueous solution by means of the membrane inlet mass spectrometry technique (MIMS). This technique is based on mass spectrometry detection using a semipermeable membrane for the inlet of gases dissolved in liquid solutions. MIMS is applied to the study of gas evolving reactions taking place at electrodes made from platinum nanoparticles supported on carbon (Pt/C), and immersed in 0.5 M H2SO4 solution. Potentiodynamic experiments under MIMS detection show the formation of carbon oxidation products like CO2, CO and HCOOH. The oxidation of carbon is accelerated in the presence of Pt eletrocatalyst. Instability of a Pt/C electrode starts at 0.35 VNHE, close to the C/CO2 thermodynamic potential, reflected by the detection of CO2 evolution. Partial oxygen reduction to hydrogen peroxide produces carbon corrosion at even lower potentials due to chemical reactivity. The corrosion rate is in the order of 10 - 9 A cm C - 2 (related to total carbon area) at room temperature. The results are of interest for stability studies on proton exchange membrane fuel cell (PEMFC) electrodes.