Inhibitory Effect Of CO2 Research Articles

Responses of Arabidopsis and wheat to rising CO2 depend on nitrogen source and nighttime CO2 levels.

A major contributor to the global carbon cycle is plant respiration. Elevated atmospheric CO2 concentrations may either accelerate or decelerate plant respiration for reasons that have been uncertain. We recently established that elevated CO2 during the daytime decreases plant mitochondrial respiration in the light and protein concentration because CO2 slows the daytime conversion of nitrate (NO3 (-)) into protein. This derives in part from the inhibitory effect of CO2 on photorespiration and the dependence of shoot NO3 (-) assimilation on photorespiration. Elevated CO2 also inhibits the translocation of nitrite into the chloroplast, a response that influences shoot NO3 (-) assimilation during both day and night. Here, we exposed Arabidopsis (Arabidopsis thaliana) and wheat (Triticum aestivum) plants to daytime or nighttime elevated CO2 and supplied them with NO3 (-) or ammonium as a sole nitrogen (N) source. Six independent measures (plant biomass, shoot NO3 (-), shoot organic N, (15)N isotope fractionation, (15)NO3 (-) assimilation, and the ratio of shoot CO2 evolution to O2 consumption) indicated that elevated CO2 at night slowed NO3 (-) assimilation and thus decreased dark respiration in the plants reliant on NO3 (-). These results provide a straightforward explanation for the diverse responses of plants to elevated CO2 at night and suggest that soil N source will have an increasing influence on the capacity of plants to mitigate human greenhouse gas emissions.

Synergistic Suppression of Cortical Spreading Depression under NR2A and NR2B Inhibition

Cortical spreading depression (CSD) is a transient synaptic excitation, followed by depression, which can propagate slowly across cortex, subcortex and retina. CSD is implicated in migraine with aura and may lead to migraine pain. CSD can be suppressed by inhibition of both NR2A and NR2B containing N-methyl-D-aspartic acid (NMDA) receptors. However, whether there is a synergistic effect of co-inhibition of NR2A and NR2B containing receptors on CSD remains unknown. In this study, an efficient in vitro model of migraine with intrinsic optical imaging approach was applied to address this role of co-activation of both NR2A and NR2B in CSD. The results showed that co-application of NVP-AAM077, a drug selectively targeting for NR2A and Ro 25-6981, a drug selectively targeting for NR2B containing receptors, showed synergistic inhibitory effects on propagation rate and the magnitude of CSD in a concentration dependent manner in chick retina. Inhibition of CSD propagation was also observed by a clinical acceptable drug that antagonizes both NR2A and NR2B containing receptors, memantine, at 10 μM. These data suggest that combinational use of antagonists selectively targeting NR2A and NR2B containing receptors could be a useful strategy for preventative treatment of migraine with improved efficacy with potential alleviated side effects.

Inhibition effect of CO on hydrogen permeability of Pd–Ag membrane applied in a microchannel module configuration

The surface adsorption effect of CO on the hydrogen permeability of a 12.5 micron-thick Pd77Ag23 membrane has been evaluated quantitatively under experimental conditions close to the operating conditions of the highly-efficient membrane reformer (MRF) system developed by Tokyo Gas. The permeability of the membrane was measured in the conditions of CO concentration between 1 and 5 vol.% at a temperature and pressure of up to 500 °C and 0.6 MPa, respectively. High feed flow rates and a microchannel module configuration were applied in the flux measurements to ensure that the results are obtained with limited influence of concentration polarization adjacent to the membrane surface and hydrogen depletion along the microchannel length. While the CO inhibition effect was close to negligible at 500 °C, it was significant at lower temperatures. At a feed pressure of 0.2 MPa, the CO inhibition effect was only 0.2% at a CO concentration of 1 vol.% and the effect was 3.6% at a CO concentration of 5 vol.% at 500 °C. The CO inhibition effect were 3.4% for 1 vol.% CO and 14.1% for 5 vol.% CO at 400 °C. Measurements were also carried out at a high feed pressure of 0.6 MPa to evaluate the pressure dependence of the CO inhibition effect. The CO inhibition effect decreased to 0.7% at a CO feed concentration of 5 vol.% at 500 °C. Lower CO inhibition effect were also observed at 450 and 400 °C compared to the data obtained with the feed pressure of 0.2 MPa, while the inhibition levels were almost the same at 350 °C. Though the CO inhibition effect is larger at a lower feed pressure of 0.2 MPa, the effect was only 0.2% at 1 vol.% CO at 500 °C, which is close to the operating conditions of the MRF system. This study quantitatively revealed that the CO inhibition effect on hydrogen flux is extremely small when the membrane is operated at temperatures equal to or higher than 500 °C, even for state-of-the-art thin membranes. The performance of the Tokyo Gas MRF seems thus mainly limited by concentration polarization effects.

Gasification kinetics of char from olive tree pruning in fluidized bed

The gasification rate of char from olive tree pruning was measured in a fluidized bed at temperatures between 760 and 900°C. Experiments were carried out using gas mixtures containing H2O, CO2, H2, CO and N2 in various proportions. Two kinetic equations were obtained, one for the char gasification rate with H2O, taking into account the inhibition effect of H2, and another for gasification with CO2, including the inhibition effect of CO. The kinetic expressions account for the effect of temperature, gas composition, and the extent of carbon conversion. The influence of the gas composition and temperature was expressed by the Langmuir–Hinshelwood model, whereas an nth order kinetic model was used to account for the variation of the reaction rate with the extent of conversion. The reaction rate with H2O was observed to be 3–4times faster than that with CO2. Inhibition effects caused by CO and H2 were significant. It was found that the gasification rate in a mixture containing CO2 and H2O simultaneously can be estimated from addition of the individual rates with CO2 and H2O.

Effect of Carbon Dioxide on the Reactivity of the Oxidation of Boron Particles

AbstractCarbon dioxide produced in the primary combustion of propellants apparently affects the combustion of boron. In this study, the thermodynamic and kinetic properties of the combustion of boron particles in a CO2 environment (solely or as a mixture with other gases) were investigated using thermogravimetric analyses. For the combustion of boron in an atmosphere containing 10 % oxygen, in addition to a large initial weight gain, a second increase in weight was observed when the temperature reached 1150 °C. However, when the combustion was carried out in pure CO2 atmosphere, the sample lost weight at temperatures above 1300 °C. The above results indicated that the layer of boron oxide covering the boron particles had a significant effect on the combustion process. With a limiting concentration of O2 (10 %), the initial temperature and effective activation energy slightly decreased as the content of CO2 increased from 0 to 30 %. However, a further increase in the CO2 content (50 %) increased the effective activation energy, indicating the inhibitory effects of CO2 at higher concentrations. Furthermore, the weight and the rate of weight gain gradually increased with increasing CO2 content. This behavior was attributed to the improvement in the diffusion of the oxidant. This study conclusively revealed that the inclusion of an optimal level of CO2 in a reaction environment containing O2 facilitated the combustion of boron particles.

Coal Char Gasification in the Mixture of H2O, CO2, H2, and CO under Pressured Conditions

The kinetic study of coal char gasification at elevated pressure is very limited and much less than that at atmospheric pressure, especially in the mixture of H2O, CO2, H2, and CO. The inhibition effect of H2 and CO and a suitable reaction model are both needed to be studied under pressured conditions. A Langmuir–Hinshelwood (L-H) type model has been widely adopted to describe coal char gasification at atmospheric pressure. But its applicability to pressured conditions is questionable. In this paper, the experiments of coal char gasification in the mixture of H2O, CO2, H2 and CO were carried out using a modified pressured thermogravimetric analyzer (PTGA) system at 0.5 MPa and within 1148–1198 K. Experimental results indicate that the gasification reaction rates of H2O and CO2 under pressured conditions are much higher than those at atmospheric pressure, and the inhibition effects of H2 and CO are also stronger. The kinetic parameters in L-H model were determined from pressured pure H2O and CO2 gasification (N2 as diluent). And the applicability of L-H model to pressured conditions was verified. It is shown that the L-H models based on common or separate active sites assumptions could not give satisfactory predictions to experimental data. Finally, we proposed a modified L-H model. This model only needs several extra experiments to calculate the modification factor, and can describe char gasification in the mixture of H2O, CO2, H2 and CO under pressured conditions very well.

Deoxygenation of decanoic acid and its main intermediates over unpromoted and promoted sulfided catalysts

The transformation of decanoic acid, used as a model oxygenated compound, was first studied over Mo/Al2O3 at 340°C under 4MPa of total pressure (H2 pressure equal to 2.72MPa) in a fixed-bed reactor. The deoxygenation of decanoic acid is considered to proceed through two main routes: (i) the HDO pathway yielding decenes and decane as ultimate hydrocarbons, oxygen being removed as water; (ii) the DEC pathway involving a decarbonylation reaction and mainly leading to nonene isomers, oxygen being discarded as water and carbon monoxide. Other products such as oygenates (mainly decanal and 1-decanol) and sulfur-containing products (mainly 1-decanethiol) appeared as intermediates of the HDO way. A significant inhibiting effect of carboxylic acid on the deoxygenation of decanal was highlighted. A general reaction scheme of deoxygenation of decanoic acid over sulfided catalysts was established. Considering a sulfur vacancy as an active site, deoxygenation reaction mechanisms were proposed involving a cationic species as a common intermediate between the HDO and the DEC pathways. The effect of Co and Ni on the deoxygenation rate of decanoic acid was measured by using both CoMo/Al2O3 and NiMo/Al2O3. The DEC route was strongly promoted by Co and Ni, whereas an inhibiting effect of Co and Ni was observed on the HDO route. It was assumed that the promoter effect on the DEC route may result from an increase of the basicity of sulfur anions neighbouring of Co or Ni present in the sulfided promoted phase.

An experimental and detailed chemical kinetic modeling study of hydrogen and syngas mixture oxidation at elevated pressures

The oxidation of syngas mixtures was investigated experimentally and simulated with an updated chemical kinetic model. Ignition delay times for H2/CO/O2/N2/Ar mixtures have been measured using two rapid compression machines and shock tubes at pressures from 1 to 70bar, over a temperature range of 914–2220K and at equivalence ratios from 0.1 to 4.0. Results show a strong dependence of ignition times on temperature and pressure at the end of the compression; ignition delays decrease with increasing temperature, pressure, and equivalence ratio. The reactivity of the syngas mixtures was found to be governed by hydrogen chemistry for CO concentrations lower than 50% in the fuel mixture. For higher CO concentrations, an inhibiting effect of CO was observed. Flame speeds were measured in helium for syngas mixtures with a high CO content and at elevated pressures of 5 and 10atm using the spherically expanding flame method. A detailed chemical kinetic mechanism for hydrogen and H2/CO (syngas) mixtures has been updated, rate constants have been adjusted to reflect new experimental information obtained at high pressures and new rate constant values recently published in the literature. Experimental results for ignition delay times and flame speeds have been compared with predictions using our newly revised chemical kinetic mechanism, and good agreement was observed. In the mechanism validation, particular emphasis is placed on predicting experimental data at high pressures (up to 70bar) and intermediate- to high-temperature conditions, particularly important for applications in internal combustion engines and gas turbines. The reaction sequence H2+HO˙2↔H˙+H2O2 followed by H2O2(+M)↔O˙H+O˙H(+M) was found to play a key role in hydrogen ignition under high-pressure and intermediate-temperature conditions. The rate constant for H2+HO˙2 showed strong sensitivity to high-pressure ignition times and has considerable uncertainty, based on literature values. A rate constant for this reaction is recommended based on available literature values and on our mechanism validation.

A comparative study on the kinetics of carbon dioxide reforming of methane over Pt–Ni/Al2O3 catalyst: Effect of Pt/Ni Ratio

Kinetics and surface reaction mechanism of CO2 reforming of methane (CDRM) was studied over 0.2%Pt–15%Ni/Al2O3 and 0.3%Pt–10%Ni/Al2O3 catalysts in order to determine the effect of Ni/Pt loading ratio on kinetic behavior. The simple power-law type rate expressions obtained for 0.3%Pt–10%Ni/Al2O3 and 0.2%Pt–15%Ni/Al2O3 have reaction orders of 1 and 1.09 for CH4 and 0.87 and 1.40 for CO2, respectively, confirming methane consumption rate for 0.2%Pt–15%Ni/Al2O3 sample is more sensitive to the increase in partial pressure of CO. The comparative analysis of meaningful surface reaction models for the catalysts and the optimized model parameters obtained revealed that the surface reaction mechanisms are completely different. CO inhibition effect is stronger and CO2 utilization is suppressed on the catalyst with high Ni:Pt loading ratio. On the other hand, with a decrease in Ni:Pt loading ratio, CH4 adsorption becomes weaker, ability of utilizing CO2 as the oxygen source gets stronger and CO inhibition effect is practically eliminated.

Investigations of the Effects of Epigallocatechin-3-Gallate and Co<sup>2+</sup> on Cal-27 Cells <i>In Vitro</i>

Epigallocatechin gallate (EGCG), a major polyphenol of green tea, has been shown to inhibit the growth of various cancer cell lines. Co2+ is one of essential trace elements of human nutrition, both lack and excess have adverse effects on health.In this research, MTT assays were applied to investigate the effects of Co2+, EGCG and their coactions on Cal-27 cells, The results show that Co2+ and EGCG inhibited the growth of Cal-27 cells in a time-and dose-dependent model, and inhibition effects were extremely dependent on their concentrations, added orders and [Co2+]/[EGCG] ratio. Inhibitory effects of Co2+ could be decreased in the presence of EGCG. LC/MS analysis showed that a new component arised when EGCG and Co2+ were mixed together. It was inferred that the new components were [EGCG-2Co] and [EGCG-Co], and the process might be responsible for the observed effect of the bioactivities of Co2+ against Cal-27 cells.

Catalyst ‘light-off’ experiments on a diesel oxidation catalyst connected to a diesel engine—Methodology and techniques

A methodology was developed, which helped to investigate the ‘light-off’ characteristics of a real diesel oxidation catalyst (DOC) while it was connected to a diesel engine. As a demonstration of the technique, trials were performed on a Ford 2.0L engine, with a Pt on γ-alumina DOC (o.d.=106mm; length=114mm). By operating the engine at a constant speed (e.g. 2000rpm), it was shown that when the engine torque was varied (e.g. from 5 to 47Nm), the gas inlet temperature to the DOC could also be varied (e.g. from 146 to 285°C), while the gas composition and the mass flow of gas remained relatively constant—this enabled more scientific studies of catalyst ‘light-off’ to be performed on a real exhaust system. Experiments were also performed with higher background levels of a reactant (e.g. CO concentrations=3000, 4000 and 5000ppm), and hysteresis between ‘light-off’ and ‘light-down’ was observed. It was also shown how valuable additional information may be obtained from experiments using a thin-slice DOC (o.d.=106mm; length=5mm), and the CO inhibition effect was demonstrated on a real engine exhaust.

Effects of reaction conditions on the acid-catalyzed hydrolysis of miscanthus dissolved in an ionic liquid

Experiments were conducted to study the effects of reaction conditions on the hydrolysis of miscanthus dissolved in 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]) catalyzed by H2SO4. It was determined that while there is a small co-inhibition effect associated with the simultaneous hydrolysis of the cellulosic and hemicellulosic portions of miscanthus, the largest rate decreases were observed for the hydrolysis of the hemicellulosic portion. This rate decrease was attributed to the chemical linkage between hemicellulose and lignin in miscanthus, which could be broken with chemical pretreatment. While chemical pretreatment increased the rate of the hydrolysis of the hemicellulosic component, delignification showed no further benefit. The rate of hydrolysis was determined to be first order in concentrations of β-1,4 glycosidic linkage and acid, and zero order in water concentration. The activation energy for the hydrolysis of the glycosidic linkages in the cellulosic and hemicellulosic components were determined to be 95 kJ mol−1 and 114 kJ mol−1 respectively. Progressive addition of water during the first hour of the reaction increased conversion and selectivity to saccharine products, while limiting dehydration of the sugars formed. The conversion of the cellulosic portion of miscanthus could be increased after the first hour of the reaction by increasing the reactor temperature. While miscanthus is only partially soluble in [Emim][Cl], it was found that the initial miscanthus loading could be increased to 9 wt% before significant yield decreases attributed to solubility limitations of the cellulosic component were observed. By proper adjustment of reaction conditions, it was possible to achieve yields of sugars approaching 84% from the cellulosic and hemicellulosic components of miscanthus, with minimal dehydration of the sugars to furans.

RESPIRATION RATE OF POMEGRANATE ARILS AS AFFECTED BY O2 AND CO2, AND DESIGN OF MODIFIED ATMOSPHERE PACKAGING

The effect of CO 2 and O 2 on respiration rate of pomegranate arils was determined and suitability of common packaging materials was evaluated for designing MAP. Respiration rate of arils from a local pomegranate cultivar, 'Hicaz', was measured at different O 2 (2, 10, 21%) and CO 2 (0, 10 20%) concentrations at 4°C. Oxygen consumption and CO 2 production rate of the arils were modeled by enzyme kinetics based models. Inhibitory effect of CO 2 on respiration rate was evaluated by four types of inhibition models (competitive, uncompetitive, combination of competitive and uncompetitive, non-competitive types). MAP design was conducted for different package sizes to determine the characteristic of required packaging materials for fresh pomegranate arils. Respiration rate of the arils was significantly affected by O 2 and CO 2 concentrations. As O 2 concentration decreased respiration rate decreased. Respiration rate decreased by 10 and 20% CO 2 levels. No difference between the effect of 10 and 20% CO 2 concentration was detected. The competitive inhibition model for respiration rate can be used in package design for the arils. MAP design analysis indicated that common packaging materials (LDPE, PP) did not provide desired atmospheric conditions for pomegranate arils. Required packaging material's permeabilities were determined for several package sizes from 250 g to 2 kg.

Gasification of woody biomass char with CO 2: The catalytic effects of K and Ca species on char gasification reactivity

The effects of alkali and alkaline earth metals such as potassium (K) and calcium (Ca) on CO 2 gasification reactivity of Japanese cypress (hinoki) char under various temperatures (1123–1223 K) and CO 2 concentration (20–80 vol.%) were studied using thermal gravimetric analysis. The presence of K and Ca compounds in char improved the reactivity of hinoki char for CO 2 gasification catalytically. It was also confirmed that K and Ca compounds can be supported on char to exhibit an enhanced catalytic effect during CO 2 gasification of K-char and Ca-char. The char gasification rate increased with the increase of CO 2 concentration at higher temperatures (1173–1223 K), however at lower temperature (1123 K) the gasification rate decreased at 80% CO 2. The retardation of char gasification rate at higher CO 2 concentration is caused by the inhibition effect of CO: CO is disproportionated on alkali metal catalysts to CO 2 and carbon, and affected the CO 2 gasification rate. The dependence of char gasification rate on reaction temperature yielded a straight line in an Arrhenius-type plot which indicated that there was no significant change in the gasification mechanism in the temperature range of 1123–1223 K.

Inhibition by CO and Polarization in Pd-Based Membranes: A Novel Permeation Reduction Coefficient

In this Article, a novel permeation reduction coefficient (PRC) is defined and used to take into account the presence of both inhibition by CO and concentration polarization in hydrogen permeation through Pd-based membranes. The usefulness of this coefficient consists in the possibility of describing simply, but at the same time powerfully, the behavior of the membrane subject to the combined effect of inhibition and polarization. According to this approach, the effective permeance, which is generally unknown because it depends on these two phenomena, can be directly evaluated by multiplying the "clean" intrinsic membrane Sieverts permeance (measurable by simple pure hydrogen permeation tests) by a PRC function, that is, [effective permeance] = (1-PRC) [clean Sieverts permeance]. The values of PRC are evaluated by means of a complex model that takes into account the several elementary permeation steps, in which the inhibitory effect of CO is also considered as well as the concentration polarization. The membrane behavior is evaluated in terms of some "performance maps", where PRC and other two coefficients (concentration polarization coefficient (CPC) and inhibition coefficient (IC)) are reported as functions of several operating conditions (hydrogen molar fraction, CO partial pressure, and upstream total pressures). Therefore, these maps provide a useful tool to estimate directly the main design parameter (the overall permeance) in situations where complex transport and kinetic phenomena affect the membrane performances, allowing the membrane performance to be estimated much better and the separation equipment to be better designed.

Impact of CO on the transformation of a model FCC gasoline over CoMoS/Al2O3 catalysts: A combined kinetic and DFT approach

The selective hydrodesulfurization (HDS) of FCC gasoline is a key catalytic process for reducing sulfur content in gasoline. In addition, 5.75% of the European fuels used for transportation will have to incorporate biofuels, which implies that gasoline hydrotreatment will treat feeds containing various oxygenated compounds including by-products such as CO, CO2 or H2O. In the present work, we focus on the effect of CO partial pressure on the transformation of a model FCC gasoline composed of 2-methylthiophene (2MT) and 2,3-dimethylbut-2-ene (23DMB2N) molecules, over a alumina supported CoMoS catalyst. A negative and reversible impact of carbon monoxide on the conversion of 2MT and 23DMB2N is found. Moreover, the hydrodesulfurization (HDS) of 2MT alone is much more inhibited (30%) than hydrogenation (HYD) of 23DMB2N alone (10%). In contrast, when considering the model feed where 23DMB2N and 2MT are mixed together, the loss of HDS and HYD activities is comparable whatever the CO partial pressure. Density functional theory (DFT) calculations of CO adsorption on the S- and M-edge sites of the CoMoS particles show that CO adsorption is strongly favored with respect to olefin and 2MT adsorption on both types of sites, which explains its strong inhibiting effect on HYD and HDS. A rational explanation of the different inhibiting effects of CO observed on model molecules alone and model feed is proposed in correlation with the nature of the active S- and M-edge sites present on the hexagonal CoMoS particles and involved either in HDS or in HYD reactions.

Effect of copper loading on copper-ceria catalysts performance in CO selective oxidation for fuel cell applications

Copper–ceria catalysts with three different Cu loadings (1, 7 and 15 wt%) were prepared by incipient wet impregnation, dried at 120 °C and calcined in air at 500 °C. The as-prepared catalysts were characterized by XRD, BET, Diffuse Reflectance Spectroscopy (DRS–UV–visible), Raman spectroscopy, CO and H 2-TPR, CO-TPR, CO-TPD and Oxygen Storage Capacity (OSC) measurements (with CO and O 2 concentration step-changes). The results indicated a good dispersion of copper for catalysts with 1 and 7 wt% Cu; however, bulk CuO was present for catalyst with 15 wt% Cu loading. Catalyst with 7 wt% Cu was observed to have very high capacity to release lattice oxygen to oxidize CO at low temperature. Activity results for CO oxidation in the absence and in the presence of 60% H 2, demonstrated a very similar performance for catalysts with 7 and 15 wt% Cu (both with T 100 = 112 °C), and much better than that of catalyst loaded with 1 wt% Cu. Catalyst with 7 wt% of copper shows very high activity (100% in a wide temperature window) and selectivity (higher than 85%), which makes an attractive for its use in purification of hydrogen for fuel cell applications. The presence of a mixture of CO 2 and H 2O inhibited catalyst activity, with CuO/CeO 2 catalyst with 7 wt% Cu exhibiting the best performance in the overall reaction temperature range. This could be attributed to the presence of highly disperse copper, only part of it in deep interaction with ceria. The effect of O 2/CO ratio ( λ) and the potential reversibility of the inhibitory effect of CO 2 and H 2O were also investigated.

Effect of heat stress on actin cytoskeleton and endoplasmic reticulum of tobacco BY-2 cultured cells and its inhibition by Co2+

Temperature stress such as heat, cold, or freezing is a principal cause for yield reduction in crops. In particular, heat stress is very common and dangerous for plants since this stress can impact several plant and cellular functions. In spite of their role in sensing local stress and in controlling fundamental processes including PCD, the responses of cellular structures and organelles to heat stress are poorly investigated. In this work, we investigated the possible changes induced by mild heat stress, medium heat stress, and heat shock (HS; 5 min at 35 degrees C, 45 degrees C, or 50 degrees C, respectively) on actin cytoskeleton and endoplasmic reticulum (ER) of tobacco BY-2 cultured cells. While mild and medium heat stresses are ineffective, HS induces depolymerization of actin microfilaments and changes in ER morphology accompanied by accumulation of the HSP70 binding protein (BiP). These effects of HS are prevented by the inhibitor of ethylene production Co(2+). While the analyzed cell structures do not seem to be involved in the establishment of mild and medium heat stresses at least in this experimental system, the strong modifications induced by the treatment at 50 degrees C suggest that actin cytoskeleton and ER may be involved in the responses to HS. Besides, the inhibiting effect of Co(2+) suggests a role for ethylene as a regulative molecule in the responses to HS here observed.

The influence of the CO inhibition effect on the estimation of the H 2 purification unit surface

The CO inhibition effect on H 2 permeance through commercial Pd-based membranes was analysed by means of permeation measurements at different CO compositions (0–30% molar) and temperatures (593–723 K) with the aim to determine the increase of the membrane area in order to compensate the H 2 flux reduction owing to the CO inhibition effect. The permeance of H 2 fed with carbon monoxide was observed to decrease with respect to the case of pure hydrogen. At 647 K the H 2 permeance of a pure feed of 316 μmol m −2 s −1 Pa −0.5 reduces progressively until 275 μmol m −2 s −1 Pa −0.5 when 15% or more of CO is present in the system, until it reaches a plateau at 20%. The inhibition effect occurring when CO is present in the feed stream reduces with the progressive temperature increase; the reduction of the permeance decreases exponentially by 23% at 593 K and by 3% at 723 K with 10% of CO. The inhibition effect is seen to be reversible. An H 2 flux profile in a Sieverts' plot shows the effect produced by the increase of the CO composition along the Pd-based membrane length. The H 2 flux profile allows the area of a Pd-based membrane to be evaluated in order to have the same permeate flow rate of H 2 when it is fed with CO or as a pure stream. Moreover, a qualitative comparison between the H 2 flux profiles and a previously proposed model has been carried out. Although studies on the CO inhibition and dilution effects are present in the literature, however, an appropriate evaluation of the H 2 membrane purification unit surface using measurements of permeances of H 2 mixed with CO has until now never been proposed. This information proves important in the design of a hydrogen purification unit.

Carbon partitioning in N2 fixing Medicago sativa plants exposed to different CO2 and temperature conditions.

Many of the studies analysing the CO2 effect on plant development have been conducted in optimal growth conditions. Furthermore, although some of those studies suggest that legumes might show a steady productivity increase with rising CO2, the role of nodule activity on the plant responsiveness to predicted atmospheric CO2 enhancement is not well understood. In this study, C (metabolism and allocation) and N (nodule activity) interaction between the plant and the bacterial symbiont during the photosynthetic acclimation of N2-fixing alfalfa (Medicago sativa L. cv. Aragón) plants exposed to elevated CO2 and temperature conditions was analysed. The plants were grown in temperature gradient greenhouses (TGG) where, in the case of elevated CO2 treatments, the isotopic 13C/12C composition (δ13C) inside the TGG was modified. Compared with the corresponding temperature treatment, exposure to 700 μmol mol-1 CO2 enhanced dry mass (DM) of plants in elevated temperature treatments (26%), whereas no significant effect was detected in ambient temperature treatments. The δ13C data revealed that although all the carbon corresponding to leaf total organic matter (TOM) came from newly assimilated C, plants exposed to elevated CO2 did not develop strong sink activity (especially in ambient temperature conditions). Leaf carbohydrate build-up induced reduction in the Rubisco (E.C. 4.1.1.39) carboxylation capacity of plants. Despite this reduction in Rubisco content, plants exposed to elevated CO2 conditions maintained (at ambient temperature) or increased (at elevated temperature) photosynthetic rates (measured at growth conditions) by increasing N use efficiency. The larger C sink strength of nodules in plants grown at elevated CO2 and temperature conditions did not contribute towards overcoming photosynthetic acclimation. Further, the inhibitory effect of CO2 on nodule total activity was caused by a large depletion in total soluble protein (TSP) of nodules. Depletion of leaf N demand, together with the reduction in nodule carbohydrate availability (as reflected by the nodule starch concentration), negatively affected the nodule TSP content and enzymatic activity.