O2 In Helium Research Articles

Active Probing of a RuO2/CZ Catalyst Surface as a Tool for Bridging the Gap Between CO Oxidation Catalytic Tests in a Model and Realistic Exhaust Gas Stream.

Herein, we present a paper that attempts to bridge the gap between CO oxidation catalytic tests performed in a model stream and a more realistic exhaust gas stream by incorporating characterization methods that allow for active probing of the catalyst surface. The results have shown that it is not just the abundance of a given type of species on the surface that impacts the activity of a system but also the ease of extraction of ions from their surface (time-of-flight secondary ion mass spectrometry) and the response of the support to change in the feed composition (dynamic in situ X-ray diffraction (XRD) with variable atmosphere). The study utilizes the method of doping a catalyst (RuO2/CZ) with a small amount of alkali-metal (K+ or Na+) carbonates in order to slightly modify its surface to gain insight into parameters that may cause discrepancies between model stream activity and complex stream activity. The most pronounced difference is that in the model stream, which contains only CO and O2 in helium, both alkali ions improve the activity of the system at temperatures around 175 °C, whereas in the complex stream, which mimics the exhaust stream from a diesel engine under oxygen lean conditions, the K+-doped catalyst is slightly worse than RuO2 /CZ and RuO2 + Na+/CZ and much worse in propane combustion. The total hydrogen consumption values (temperature-programmed reduction) and the Oads/Olatt ratios (X-ray photoelectron spectroscopy) both place the RuO2 + K+/CZ system between the other two and hence provided no reason for the unusual behavior of the K+-doped catalyst. In contrast, both in situ XRD measurement tests and ToF SIMS results show a pronounced difference between the RuO2 + K+/CZ catalyst and the other two systems, which indicates that the interaction of the surfaces with the reagents might be the cause of the discrepancy. The CO2-TPD results show that this system retains more CO2, i.e., the product, at adsorption sites, which might reduce the adsorption of other reagents, i.e., oxygen ions, CO, and propane, hence lowering the overall activity of the system.

The influence of oxygen concentration on the hollow cathode discharge in He/O2 mixed gas

Hollow cathode discharge in He/O2 mixed gas is simulated using a two-dimensional fluid model for the first time. The model contains 15 particles and 66 reactions. The evolutions of discharge current, electric field, charged and reactive particles with different oxygen concentrations are obtained. The primary mechanisms of generation and loss for particles under different oxygen concentrations are discussed. The results show that the added O2 in helium has both positive and negative effects on the discharge. The discharge does not monotonically change with the increasing oxygen concentration. When the oxygen concentration is low, oxygen admixture could enhance the discharge, that is, the discharge current, radial electric field, electron density, density, O density, and the O(1D) density increase with the increase of oxygen concentration. When the oxygen concentration is high, it will weaken discharge, that is, the discharge current, radial electric field, electron density, density, O density, and the O(1D) density decrease with the increase of oxygen concentration. The main reactive particles in discharge are O and O(1D). These densities are much higher than the density of charged particles. The optimal oxygen concentration for O and O(1D) is 0.5% and 0.4%, and the corresponding maximum density is 4.34 × 1013 cm−3 and 1.50 × 1013 cm−3. The generation and loss rates for these particles at different oxygen concentrations are calculated, which contributes to the change in particle densities.

The kinetics of the oxidation of ammonia on a V2O5/TiO2 SCR catalyst deactivated in an engine rig. Part I. Determination of kinetic parameters by simulation

It is shown how the deactivation of a diesel SCR (Selective Catalytic Reduction) catalyst by compounds in the exhaust gases influences the kinetics of the catalyst. Results are given for the fresh (4.56 % V2O5/TiO2) catalyst and the ones used in the rig for 890 h and 2299 h. The reactions of 700 ppm NH3 and 2 % O2 in Helium yielded N2, N2O, and NO at increasing temperatures. Simulations were performed with COMSOL Multiphysics using a 3-D model of the catalyst system. The experimental values of the products N2, N2O, and NO were very nicely fitted by the kinetic model used. All three ammonia oxidation reaction rates were of the first order in the concentration of NH3. A preliminary study using non-isothermal conditions showed the maximal temperature increase to be 0.15 K. Thus, further simulations were done with an isothermal model. The deactivation reduces the pre-exponential factors and the activation energies for the formation of N2, N2O, and NO. The formation of N2 is not substantially influenced by deactivation. The changes in the kinetics of the catalytic NH3 oxidation by deactivation is reported for the first time in the present study.

A novel dual‐isotope labelling method for distinguishing between soil sources of N2O

We present a novel 18O-15N-enrichment method for the distinction between nitrous oxide (N2O) from nitrification, nitrifier denitrification and denitrification based on a method with single- and double-15N-labelled ammonium nitrate. We added a new treatment with 18O-labelled water to quantify N2O from nitrifier denitrification. The theory behind this is that ammonia oxidisers use oxygen (O2) from soil air for the oxidation of ammonia (NH3), but use H2O for the oxidation of the resulting hydroxylamine (NH2OH) to nitrite (NO2-). Thus, N2O from nitrification would therefore be expected to reflect the 18O signature of soil O2, whereas the 18O signature of N2O from nitrifier denitrification would reflect that of both soil O2 and H2O. It was assumed that (a) there would be no preferential removal of 18O or 16O during nitrifier denitrification or denitrification, (b) the 18O signature of the applied 18O-labelled water would remain constant over the experimental period, and (c) any O exchange between H(2)18O and NO3- would be negligible under the chosen experimental conditions. These assumptions were tested and validated for a silt loam soil at 50% water-filled pore space (WFPS) following application of 400 mg N kg-1 dry soil. We compared the results of our new method with those of a conventional inhibition method using 0.02% v/v acetylene (C2H2) and 80% v/v O2 in helium. Both the 18O-15N-enrichment and inhibitor methods identified nitrifier denitrification to be a major source of N2O, accounting for 44 and 40%, respectively, of N2O production over 24 h. However, compared to our 18O-15N-method, the inhibitor method overestimated the contribution from nitrification at the expense of denitrification, probably due to incomplete inhibition of nitrifier denitrification and denitrification by large concentrations of O2 and a negative effect of C2H2 on denitrification. We consider our new 18O-15N-enrichment method to be more reliable than the use of inhibitors; it enables the distinction between more soil sources of N2O than was previously possible and has provided the first direct evidence of the significance of nitrifier denitrification as a source of N2O in fertilised arable soil.

In-Situ Soft X-ray Absorption of Over-exchanged Fe/ZSM5

In-situ soft X-ray absorption spectroscopy (XAS) has been applied to study the iron redox behavior in over-exchanged Fe/ZSM5. The Fe L2,3 XAS and O K spectral shapes of the Fe/ZSM5 surface have been measured during heat treatments and reduction/oxidation cycles. Charge-transfer multiplet calculations provide a detailed understanding of the L2,3 spectra of iron in Fe/ZSM5. The oxidized form of Fe/ZSM5 contains FeIII ions in an octahedral surrounding, with a total crystal field splitting of ∼1.0 eV. This value is significantly smaller than that for Fe2O3, which is indicative of a much weaker Fe−O bonding. The reduced form of Fe/ZSM5 has FeII ions in a tetrahedral oxygen surrounding. The Fe L2,3 spectra show that iron in calcined Fe/ZSM5 is reduced in 15 min to an average valence state of 2.65, under 10 mbar of pure helium at room temperature. This value has a relative uncertainty on the order of 0.01. Heating in helium up to 350 °C under the same pressure further reduces the iron valence to 2.15. The oxygen spectra show that the autoreduction is accompanied by a loss of molecular oxygen and water. Reoxidation with 5% O2 in helium yields a valence of >2.90 after 10 min.

Influence of CO2 on storage and release of NOx on barium‐containing catalyst

A barium‐containing three‐way automotive emission catalyst was submitted to a NOx storage step in flowing lean gas mixture containing 340 ppm NO and 8 vol% O2 in helium. NOx release was carried out in the 250–550°C temperature range, either in pure helium or in the presence of a 10 vol% CO2 in helium mixture. It was shown that at 450–550°C all of the stored NOx on the barium trap can be released fastly in the CO2‐containing gas mixture or, after a longer time, in pure helium: these data show that NOx release can occur in the absence of a reducing agent. The NOx release was not complete at 350°C and did not occur at 250°C. The assisting effect of CO2 as regards to NOx release was interpreted in terms of the existence of the CO2,gas + *NO2,stored ⇌ *CO2,stored + NO2,gas equilibrium, suggesting the competitive storage of CO2 and NO2 for a unique type of barium storage sites (*).

Direct Observation of Alkali Vapor Release during Biomass Combustion and Gasification. 2. Black Liquor Combustion at 1100 °C

This study details the first application of molecular beam mass spectrometry to investigate the release of sodium, potassium, sulfur, and chlorine during black liquor combustion. Two samples, black liquor with 37.1% dry solids and a sample of dry black liquor solids, were combusted in a quartz-tube reactor at 1100 °C in 5% O2 in helium. The gaseous black liquor combustion products, including alkali metal salts, were monitored continuously and in real time during the combustion event with a molecular beam mass spectrometer (MBMS). Combustion of the dry black liquor solids occurred in multiple phases distinguished as a devolatilization phase and a char combustion phase that was arbitrarily divided into three separate phases. Combustion of the wet black liquor samples occurred in two phases, namely, a combination of water evaporation and devolatilization, and char combustion. NaCl was the most abundant gas-phase alkali-metal-containing species measured during black liquor combustion. The experimental results...

Exercise induced ventilation/perfusion inequality in the horse.

Exercise in normal human subjects causes deterioration of matching of ventilation to blood flow in the lungs, but only in about 50% of those examined. A previous study (Wagner et al. 1989) of 5 horses showed no significant worsening of ventilation/blood flow (VA/Q) relationships during heavy exercise as determined by multiple inert gas elimination technique (MIGET). Because of the small number of horses in that study and the 50% human incidence of exercise induced VA/Q mismatch, we studied an additional 6 Thoroughbreds, comparing VA/Q relationships at the walk (1.4 m/s, 0 degrees incline) and during galloping (9.6 +/- 0.3 m/s, 7% incline). Such data were collected under 4 different conditions wherein inspired gas was 1) air, 2) 21% O2 in helium, 3) 15% O2 in N2 and 4) 15% O2 in helium. Each horse exercised 4 times (morning and afternoon of 2 days, with inspired gas conditions randomised). There was a small but significant increase in VA/Q mismatch (similar under all 4 conditions). The second moment of the VA/Q distribution (determined by the MIGET) increased significantly (P < 0.01) from 0.31 +/- 0.01 at the walk to 0.38 +/- 0.02 during gallop. This increase however is small: 0.38 is well within the range of this parameter for normal human subjects (where the 95% upper confidence limit is 0.60). This study shows that a small amount of exercise induced VA/Q mismatch can occur in the horse as in man, but the mechanism remains to be elucidated and its clinical significance remains to be established.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuromuscular response to resistive unloading: helium vs. bronchodilation.

To evaluate the neuromuscular response to resistive unloading, we compared the ventilatory and occlusion pressure (P100) response of normal subjects breathing 20.9% O2 in helium (He-O2) with their response to unloading produced by inhaled atropine sulfate. During He-O2 breathing airway resistance (Raw) fell by 49% of the base-line value on air, and P100 decreased by 20.8%. Minute ventilation, tidal volume, respiratory frequency, end-tidal Pco2, inspiratory and expiratory duration, and mean inspiratory flow were not significantly different when air was replaced by He-O2. In contrast, although atropine reduced Raw by an equivalent amount, there was no change in P100. Atropine had no significant effect on other respiratory variables, although a trend toward higher minute ventilation was noted. Fowler dead space increased after atropine but was not affected by He-O2. We conclude that, unlike He-O2 unloading, atropine unloading does not cause a reduction in occlusion pressure. This may be due to the effect of atropine on anatomical dead space which stimulates ventilation sufficiently to offset the fall in neuromuscular output due to resistive unloading.

Effects of pulmonary gas embolism on circulation and respiration in the dog. V. Effect of changing breathing gas composition on pulmonary gas embolization.

It was found in previous investigations that during venous gas infusion at low rates (1--5 ml/min-1) circulatory and respiratory variables reached a constant level after about 10--15 min. The present study demonstrates that this steady state can be disturbed by changing the composition of the breathing gas mixture. Alteration from air to 21% O2 in helium rapidly increased the embolic effects up to a maximum within 1.5--2 min; in the next 5--8 min the circulatory and respiratory variables returned to their previous levels during air breathing. Reverse effects occurred when changing from 21% O2 in helium to air. Similar phenomena were seen after switching from air to pure oxygen and from 21% O2 helium to pure oxygen. However, the extent of the circulatory and respiratory changes differed depending on the composition of the respective alternating breathing gas mixtures and on the initial embolic level as determined by infusion rate and kind of infusion gas. Gas movements between intravascular bubbles and alveolar space might be responsible for these changes.

Respiratorischer Gasaustausch bei Atmung von 20,9% Sauerstoff in verschiedenen Inertgasen

in 15 patients with chronic bronchitis with or without emphysema breathing of room air was compared with breathing of 20.9% O2 in helium and in argon. Minute ventilation and alveolar ventil

The Special Relation Between Oxygen and Nitrogen in Pulmonary Injury

The lungs of post-vagotomy newborn rabbits show the lesion of hyaline membrane disease extent directly proportional to the percentage of oxygen in polybaric (0.2–3.0 Atm. Abs.) mixtures [Lab. Invest. 21: 439, 1969]. At 7% O2 lesions do not form, but all vagotomized animals die. comparative gas studies show the direct proportionality to be related to nitrogen itself, probably through physical interaction at the pulmonary interface [South. med. J. 61: 1338, 1988; Fed. Proc. 28: 654, 1969]. In 3% O2 (1 Atm.) further dissociation between mortality and pulmonary lesion is seen. 3% O2 in nitrogen is 100% lethal without vagotomy over a time course (3.0–27.0 h) questionably longer (0.02 > p > 0.01), but otherwise similar to vagolomy effects. Minimal lesions are seen in both (2–3% extent). 3% O2 in helium with or without vagotomy shows moderate lesions (19–32% extent); without vagotomy only 7% die by 24 and 40% by 48 h. 3% O2 in sulfur hexafluoride shows moderate lesions (7–15% extent) after vagotomy; without vagotomy only 15% die by 24 and 26% by 48 h. The protective effect of SF6 after vagotomy [South. med. J., ibid] is thus seen only at 20% + O2. The difference in survival without vagotomy between N2, He and SF6 is highly significant (p< 0.001), and probably due to better uptake of oxygen. These date suggest a special relation between O2 and N2, enhancing the improtance of physical attributes, molecular size, shape, etc. They also suggest a further mediation of blocking by N2 through physico-chemical imteraction which is not shown by He or SF6 in relation to O2. The limit of ‘hypoxic’ tolerance (> 3% O2) described by G. AVERY [Pediatrics 32: 801, 1963], inter alia, is thus an effect of specific interaction of oxygen and nitrogen. (Supported by the John A. Hartford Foundation, New York.)

Respiratory Arrest in Rabbits Exposed to Hypoxia after Dibenamine.

SummaryRabbits given Dibenamine 12 to 24 mg/kg in propylene glycol or ethyl alcohol by vein show sudden respiratory arrest within 3 minutes of exposure to hypoxia (circa 5% O2 in helium).