Adsorbent oxidized

Adsorbate oxidation at a reasonable rate on pure Pt electrodes occurs at potentials above ca. 500 mV RHE. The partial blockage of the surface is the reason for the low currents observed below this potential. 

According to these results methanol adsorbate seems to consist of a mixture of (C, O) and (C, O, H) particles, the actual ratio depending on the concentration and total degree of coverage. This is in good agreement with coulometric determinations of the charge ratio for methanol adsorption, Qad, (see Eqs. 2.1 to 2.3) and adsorbate oxidation, Qox (see Eqs. 2.4 to 2.6) [14,47], These results will be discussed in Section 2.1.4. 

Fig. 4.5. Mass spectroscopic detection of carbon dioxide during methanol adsorbate oxidation and Sn(IV) injection. Porous Pt electrode, real area 12.3 cm2. Procedure after methanol adsorption at 0.4 V from 10 2 M 13CH3OH/0.5 M H2S04, the electrolyte was exchanged with 0.5 M H2S04, then potential step to 0J was applied and Sn(lV) was added. Dashed line no tin added.

Fig. 4.7. Current (a) and mass intensity (b) voltammograms for methanol adsorbate oxidation without tin (dashed line) and with tin (full line). Base electrolyte dotted line. The voltammograms were recorded after applying a potential step to E0, = 0.475 V during 15 min.

In this way Sn(II) would bring oxygen-containing species to the Pt interface which are stronger adsorbed than HzO and can therefore act as oxygen donors more easily during methanol adsorbate oxidation ... 

On the other hand, Bagotzky and Vassilyev (1967) also measured the charge passed during methanol adsorption at a potential in the double-layer region and the adsorbate oxidation. The results they obtained are given in Table 3.2 and strongly suggested that the adsorbate was COH (see equations (3.45) and (3.47)). 

Fig. 9-19. Electron state density of adsorbed proton/lpndrogen redox particles on metal electrodes (a) the relative concentration of adsorbed reductant hydrogen atoms (Had) will be hitler if the Fermi level ef(h, of electrode is higher than the standard Fermi level of adsorbed redox particles, (b) the relative concentration of adsorbed oxidant...

The adsorption data is often fitted to an adsorption isotherm equation. Two of the most widely used are the Langmuir and the Freundlich equations. These are useful for summarizing adsorption data and for comparison purposes. They may enable limited predictions of adsorption behaviour under conditions other than those of the actual experiment to be made, but they provide no information about the mechanism of adsorption nor the speciation of the surface complexes. More information is available from the various surface complexation models that have been developed in recent years. These models represent adsorption in terms of interaction of the adsorbate with the surface OH groups of the adsorbent oxide (see Chap. 10) and can describe the location of the adsorbed species in the electrical double layer. 

Ammoxidation of Aromatic Hydrocarbons. - The ammoxidation of toluene with V2O5, both pure and supported on A1203, was studied by Murakami et 0/.27,46,97,98 They conclude that the catalyst is bifunctional toluene is adsorbed oxidatively on V2O5, the oxidized product is stabilized as a benzoate ion on the alumina carrier and subsequently reacts with ammonia giving benzonitrile. It was observed that the oxidation state of the vanadium oxide was close to V204 and that benzaldehyde is probably the product formed in the initial step. 

Oxidized starch loses its ability to gel, thereby making low Tfi dispersions. Glucose dialdehyde is a glucose oxidation compound used to crosslink agarose (linear) and dextran (branched) for their performance as adsorbents. Oxidized celluloses are a substitute for glues manufactured from animal by-products. 

The crystal face dependence and the activity of the various group 8-10 metals can be understood in terms of the metal-oxygen bond strength. On an active metal both O2 and H2 are dissociatively adsorbed, oxides are not formed under reaction conditions, and the heat of adsorption for Oacisis relatively low. 

The thermodynamic potential for this process lies close to OVrhe, however, CO electro-oxidation is characterized by a significant overpotential on platinum of about 0.8Vrhe- This overpotential is associated with the activation of the water (2) to produce an adsorbed oxidizing species that subsequently oxidized adsorbed CO through a Langmuir-Hinshelwood mechanism ... 

There is clear evidence that adsorbate and alloyed metal atoms on platinum surface promote CO electro-oxidation. The reduced overpotential is primarily a result of the promotion of the activation of water. The subsequent kinetics are determined by the details of a Langmuir-Hinshelwood reaction between the adsorbed oxidant (OH) and adsorbed CO. Evidence is also presented that relates this promotion (or poisoning) of CO electro-oxidation to tolerate CO in hydrogen feeds in the hydrogen electro-oxidation reaction. An alternative mechanism that may operate at low potentials [79,113] may be that the reduction in CO adsorption energy on platinum induced by Ru [86,113,114] results in a higher equilibrium concentration of nonpoisoned sites. The relative importance of these mechanisms is a function... 

Mam heterogeneous processes such as dissolution of minerals, formation of he solid phase (precipitation, nucleation, crystal growth, and biomineraliza-r.on. redox processes at the solid-water interface (including light-induced reactions), and reductive and oxidative dissolutions are rate-controlled at the surface (and not by transport) (10). Because surfaces can adsorb oxidants and reductants and modify redox intensity, the solid-solution interface can catalyze rumv redox reactions. Surfaces can accelerate many organic reactions such as ester hvdrolysis (11). 

Adsorption. Oxygen is adsorbed on clean tungsten surfaces in a variety of atomic and molecular states. At low temperature (<0 °C), oxygen is adsorbed molecularly, but at room temperature this adsorption is a precursor state to the atomic adsorption. A covered surface shows an ordered oxygen superstructure. If the temperature is increased, a more extensive coverage occurs and oxide-like structures are formed. The surface layer can be described as adsorbed oxide. 

Alkan, M. et al.. Surface properties of bovine serum albumin-adsorbed oxides Adsorption, adsorption kinetics and electrokinetic properties, Micropor. Mesopor. Mater., 96, 331, 2006. 

Figure 2 The transfer of electrons across the adsorbate/oxide interface in the course of the heterogeneous catalytic oxidation of a hydrocarbon molecule by gas phase oxygen.

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