Oxygen buffering capacity

The first developments of this type of measurements were first introduced in 1974 by Keramidas et coll, and applied to the characterization of ceramic materials [47]. Later, this method was specifically applied to the characterization of oxygen storage materials for TWC and fully described by Bernal et al. [48]. Briefly, experiments consist in injecting 5%02/He pulses (0.25 ml) every 10 seconds into the inert gas flowing on the 200 mg sample (60 ml.min ). Gas composition is followed using a gas chromatograph equipped with a TCD detector. 

Vidal et coll. [49] applied this technique to the characterization of Ceo.68Zro 32O2 mixed oxides (CZ-68/32). Three samples were characterized (i) the high surface area (HS) starting material, (ii) the low surface area (LS) sample obtained after calcination under wet air at 900°C for 140 hours and (iii) the SR sample prepared by severe reduction under H2 at 850°C for 5 hours, evacuation under He at 950°C for 1 hour and re-oxidation at 550°C with 5%02/He for 1 hour. The results are presented in Table 7.3. Authors evidenced the positive effect on OBC of both temperature (400-900°C) and a severe reduction pretreatment. 

Furthermore the influence of mixed oxides composition and redox cycling on OBC was evaluated for two complete series of HS [50] and LS [51] samples (Tables 7.4 7.5). 

While pure ceria was completely inactive at almost any temperature, the best materials for oxygen buffering were shown to be CZ-68/32 and CZ-50/50 for both series. Additionally, redox cycling was shown to have little effect on HS samples 

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Xu J, Harmer J, Li G, et al Size dependent oxygen buffering capacity of ceria nanocrystals, Chem Commun 46(11) 1887—1889, 2010. 

These measurements indicate that it is not possible to identify a single value of pe surrounding the O2/H2S interface in the environment. Redox couples do not respond to the pe of the environment with the same lability as hydrogen ion donors and acceptors. There is no clear electron buffer capacity other than the most general states of "oxygen containing" or "H2S containing." The reason for the vast differences in pec in the oxic waters is the slow oxidation kinetics of the reduced forms of the redox couples. The reduced species for which the kinetics of oxidation by O2 has been most widely studied is Mn. This oxidation reaction... 

Bacteria of the genus thiobacillus attack sulphur in the presence of moisture, oxygen and warmth (except thiobacillus denitrifleans which grows without oxygen) The acid produced may cause long term problems close to the concrete if the buffering capacity of the soil is low (7). Damage to specimens is usually restricted to the surface. 

Process control at high cell density is much more critical with regard to oxygen (see above) and nutrient supply as compared with standard batch and continuous cultures. The more intense use of medium contributes to the economy of the process, but leaves a deficit in nutritional buffer capacity. This causes rapid starvation of cells after relatively small alterations in specific nutrient supply. Therefore, cell number estimation, liquid flow/level control and the measurement of specific medium components and osmotic pressure will be dealt with here. 

When the buffering capacity of the Bornholm Basin is exhausted, weak inflows of saline and oxygen-rich water can pass that basin in depths of 50-60 m. This water frequently interleaves just below the halocline at the level of neutral buoyancy and propagates through... 

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