Oxidation species differences

Both the ionization potentials of the reduced species and the EPA properties of the oxidized species differ in different redox systems. It is, however, possible to obtciin the same standard redox potentials for different systems by coordination with suitable ligands, thus inducing... 

The percolation argument is based on the idea that with an increasing Cr content an insoluble interlinked cliromium oxide network can fonn which is also protective by embedding the otherwise soluble iron oxide species. As the tlireshold composition for a high stability of the oxide film is strongly influenced by solution chemistry and is different for different dissolution reactions [73], a comprehensive model, however, cannot be based solely on geometrical considerations but has in addition to consider the dissolution chemistry in a concrete way. 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

One extremely important point to realize is that different propellant types may have different rate-controlling processes. For example, the true double-base propellants are mixed on a molecular scale, since both fuel and oxidizing species occur on the same molecule. The mixing of ingredients and their decomposition products has already occurred and can therefore be neglected in any analysis. On the other hand, composite and composite modified-double-base propellants are not mixed to this degree, and hence mixing processes may be important in the analysis of their combustion behavior. 

The basic approach taken in the analytical studies of composite-propellant combustion represents a modification of the studies of double-base propellants. For composite propellants, it has been assumed that the solid fuel and solid oxidizer decompose at the solid surface to yield gaseous fuel and oxidizing species. These gaseous species then intermix and react in the gas phase to yield the final products of combustion and to establish the flame temperature. Part of the gas-phase heat release is then transferred back to the solid phase to sustain the decomposition processes. The temperature profile is assumed to be similar to the situation associated with double-base combustion, and, in this sense, combustion is identical in the two different types of propellants. 

The decay of the absorption of e, - was followed at 1000 nm30 or 900 nm50 where the oxidizing species do not absorb. It was found30 that esol decays by first-order kinetics. A second-order rate constant was calculated assumi ng that the decay is only by reaction with DMSO. These second-order rate constants appear to go through a maximum between 0.20 and 0.43 mole fraction of DMSO where k = 5.6 x 106 m 1 s , however, there is not a large difference between the different concentrations as the lowest value is 2.9 x 10 ... 

Consequently, the antioxidant activity of GA in biological systems is still an unresolved issue, and therefore it requires a more direct knowledge of the antioxidant capacity of GA that can be obtained by in vitro experiments against different types of oxidant species. The total antioxidant activity of a compound or substance is associated with several processes that include the scavenging of free radical species (eg. HO, ROO ), ability to quench reactive excited states (triplet excited states and/ or oxygen singlet molecular 1O2), and/or sequester of metal ions (Fe2+, Cu2+) to avoid the formation of HO by Fenton type reactions. In the following sections, we will discuss the in vitro antioxidant capacity of GA for some of these processes. 

In this study, Pt/AliOj having high activity for CO oxidation and different affinities for fee adsorption of CO and Hi was selected as a catalyst/adsorbent In a conventional packed bed reactor (PBR), fee surface of fee catalyst is dominantly covered by COads with small amotmt of Oads fee CO conversion is therefore low. Several investigations on periodic operation have illustrated feat fee reaction front wife comparable amount of fee two adsorbed species leads to enhancement of fee CO conversion. Conceptually, this type of the reaction front should be generated by application of a CMBR, as well. Figure 1 illustrates an image of... 

Co step. Previously it had been observed for the C0/AI2O3 O)/ Ni/Si02 (10), and Fe/Si02 (11, 12) systems that highly dispersed oxide species (small particles) were more difficult to reduce than their corresponding bulk or bulk-like oxides. Nucleation, interaction with the support, and reaction with the support were given as possible explanations for these differences. Further experiments are needed to determine the reasons for the observed particle size effect on the Co/Si02 system. 

In order to have more infoimation on the nature of the oxygen species active in partial and total oxidation we investigated the interaction of the hydrocarbons with the pre-oxidized surfaces of oxides where different types of surface oxygen species are formed. In particular we investigated p-type semiconductors like chromia, chromites and cobalt oxide C03O4. Moreover, we studied n-type metal oxides like FezOs, metal ferrites and CuObased catalysts. 

Different yields, mainly of the oxidizing species, were found by Koulkes-Pujo and Berthou who studied the system Fe /DMSO in the presence of high concentration of H2SO4. They found that the yields of the primary species in acidic media are Gh = 2.1 + 0.3 and Gqx (for the oxidizing species) = 3.8 + 0.4. These results are supported by studies of the system Ce /DMSO in the presence of H2SO4 . Assuming that the radicals have stoichiometric equivalence to those found in water-DMSO mixtures, we may write the observed G(-Ce ) = 13.9 + 0.4 as equal to = 3Gqx + Gh = 13.5. The difference between the yields in acidic media and for pure DMSO is due to reaction of H with the precursors of these species. 

The number of protons extracted from the film during coloration depends on the width of the potential step under consideration. As can be seen in the formulation of Fig. 26 an additional valence state change occurs at 1.25 Vsce giving rise to another proton extraction. The second proton exchange may explain the observation by Michell et al. [91] who determined a transfer of two electrons (protons) during coloration. Equation (5) is well supported by XPS measurements of the Ir4/ and Ols levels of thick anodic iridium oxide films emersed at different electrode potentials in the bleached and coloured state. Deconyolution of the Ols level of an AIROF into the contribution of oxide (O2-, 529.6 eV) hydroxide, (OH, 531.2 eV) and probably water (533.1 eV) indicates that oxide species are formed during anodization (coloration) on the expense of hydroxide species. The bleached film appears to be pure hydroxide (Fig. 27). 

The species entering the oxide do not, of course, stay as free entities but are likely to combine into hydrated oxide species of different charges and degrees of hydration. The equation describing the kinetics is... 

Secondly, the interaction of hindered amines with hydroperoxides was examined. At room temperature, using different monofunctional model hydroperoxides, a direct hydroperoxide decomposition by TMP derivatives was not seen. On the other hand, a marked inhibitory effect of certain hindered amines on the formation of hydroperoxides in the induced photooxidation of hydrocarbons was observed. Additional spectroscopic and analytical evidence is given for complex formation between TMP derivatives and tert.-butyl hydroperoxide. From these results, a possible mechanism for the reaction between hindered amines and the oxidizing species was proposed. 

FTIR spectroscopy of CO adsorbed at rt was used to monitor the state of platinum after the different calcination processes, i.e. at 500 and 300°C (Fig. 2A and B, respectively). Besides the broad band of the gaseous probe molecule, IR spectra of CO adsorbed on sample calcined at 500°C (Fig. 2A, a) showed the presence of a large band at ca. 2195 cm"1, accompanied by weak bands at ca. 2170 and 2100 cm 1, due to the presence of both platinum oxide species and Pt° clusters, whose formation is due to platinum autoreduction processes. The presence of large amounts of Pt° particles larger than 30 nm was observed by FIRTEM (data not shown). 

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