Diffusion simultaneous oxidation

In our hands, EQCM studies of this system have confirmed previous reports of y-FeOOH deposition kinetics and the chemical reaction of ferrous ions with this film after a current interruption step. Figure 12.1 depicts the simultaneous transients of anodic current (Fig. 12.1(b)) and frequency shift (A/) when a potential step (Fig. 12.1(c)) is applied from a potential where there is no reaction on gold to a potential where diffusion controlled oxidation of ferrous ions takes place. The current transient shown in Fig. 12.1(b) can be described by a diffusion process since a linear dependence of the anodic current density with t 1/2 was found as predicted by the Cottrell equation ... 

Also called nitric oxide, nitrogen monoxide or oxidonitrogen, NO is a colorless, relatively unreactive radical that is essentially insoluble in aqueous solution. Simple absorption in alkaline solutions is not effective, since it is only physically absorbed [3,4,6]. Absorption in nitric acid decreases with acid concentration [4], and oxidation with ozone to produce acidic NO2 facilitates its absorption in alkaline media [6]. Absorption of NO with simultaneous oxidation at a gas diffusion electrode in alkaline solution eliminates the need for an oxidizing agent [6] ... 

Unless the coverage of adsorbate is monitored simultaneously using spectroscopic methods with the electrochemical kinetics, the results will always be subject to uncertainties of interpretation. A second difficulty is that oxidation of methanol generates not just C02 but small quantities of other products. The measured current will show contributions from all these reactions but they are likely to go by different pathways and the primary interest is that pathway that leads only to C02. These difficulties were addressed in a recent paper by Christensen and co-workers (1993) who used in situ FT1R both to monitor CO coverage and simultaneously to measure the rate of C02 formation. Within the reflection mode of the IR technique used in this paper this is not a straightforward undertaking and the effects of diffusion had to be taken into account in order to help quantify the data obtained. 

Simultaneous generation of nitric oxide and superoxide by NO synthases results in the formation of peroxynitrite. As the reaction between these free radicals proceeds with a diffusion-controlled rate (Chapter 21), it is surprising that it is possible to detect experimentally both superoxide and NO during NO synthase catalysis. However, Pou et al. [147] pointed out that the reason is the fact that superoxide and nitric oxide are generated consecutively at the same heme iron site. Therefore, after superoxide production NO synthase must cycle twice before NO production. Correspondingly, there is enough time for superoxide to diffuse from the enzyme and react with other biomolecules. 

Since this reaction involves ions, electrons, and gas molecules in three separate phases, the edge of the o/y interface that makes contact with the gas phase /3 is often described as the three-phase (or triplephase) boundary (TPB). The concept of the TPB actually dates to the 1920s, when workers studying the oxidation of H2 on platinum introduced this concept to explain why Pt must be exposed simultaneously to both solution and gas to get significant reaction. This type of electrode, which Schmid called die diffusiongaselektrode or gas-diffusion electrode (GDE), is still called this today by workers studying solution- or polymer-based fuel cells. As... 

A fluorometric method was developed for determination of atmospheric H2O2 simultaneously with other species present at ppbv or lower levels, avoiding chromatographic separation. H2O2 is selectively collected by diffusion through a Nafion membrane, and is carried by a water stream into a reactor where it oxidizes thiamine hydrochloride (117) to a fluorescent ionic form of thiochrome (118), catalyzed by bovine hematin (75b) in alkaline solution, as shown in equation 40. The end solution containing 118 is passed through... 

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