Redox characterization

TPR is a routinaiy technique in the redox characterization of M/Ce02 and related catalysts. It has been very extensively used in comparative studies aimed at establishing the influence of variables like the chemical composition (281,341,343,344,350-353), or the high temperature ageing treatments (187,288,337,347,354), on the reducibility of ceria-based mixed oxides, both in the presence and in the absence of a supported noble metal. 

Make initial redox characterization such as the redox potentials, stability of different oxidation states, and for qualitative investigation of chemical reactions that accompany electron transfer... 

Electronic and redox characterization of the planarized species revealed surprising results. The absorption bands of 40 were of slightly shorter wavelength... 

The quantification of the reversible metal deactivation effects induced on an Au/CZ catalyst by a series of redox pre-treatments, which consecutively changed the redox state of the support, have also been investigated using the methodology discussed above/ In this investigation, FTIR and volumetric adsorption studies of CO were combined with nanoparticle size distribution data, as determined by HAADF-STEM, and redox characterization studies of the ultimate OSC, as determined by thermo-gravimetric measurements, and XPS. 

In a redox reaction, one of the reactants is oxidized while another reactant is reduced. Equilibrium constants are rarely used when characterizing redox reactions. Instead, we use the electrochemical potential, positive values of which indicate a favorable reaction. The Nernst equation relates this potential to the concentrations of reactants and products. 

As with acid-base and complexation titrations, redox titrations are not frequently used in modern analytical laboratories. Nevertheless, several important applications continue to find favor in environmental, pharmaceutical, and industrial laboratories. In this section we review the general application of redox titrimetry. We begin, however, with a brief discussion of selecting and characterizing redox titrants, and methods for controlling the analyte s oxidation state. 

The following experiments may he used to illustrate the application of titrimetry to quantitative, qtmlitative, or characterization problems. Experiments are grouped into four categories based on the type of reaction (acid-base, complexation, redox, and precipitation). A brief description is included with each experiment providing details such as the type of sample analyzed, the method for locating end points, or the analysis of data. Additional experiments emphasizing potentiometric electrodes are found in Chapter 11. 

Oxidation Reactions. Potassium permanganate is a versatile oxidizing agent characterized by a high standard electrode potential that can be used under a wide range of reaction conditions (100,133—141). The permanganate ion can participate in a reaction in any of three distinct redox couples. 

BW Beck, Q Xie, T Ichiye. Computational study of S—H S hydrogen bonds m [4Ee-4S]-type ferredoxm x-ray and NMR structures Characterization and implications for redox potentials. Protein Sci, submitted. 

A general property of these carbonyl clusters is their tendency to behave as electron sinks , and their redox chemistry is extensive. [OsioC(CO)24]" has been characterized in no less than five oxidation states (n = 0-4) though admittedly this is exceptional. 

Many oxidation-reduction reactions (nicknamed redox reactions) take place in aqueous solution. One of these was mentioned in Section 11-2.1 when we characterized acids ... 

According to our analytical results on the solid-state redox reaction of LiNi02 based on the phenomenological expression for solid-state redox potentials of insertion electrodes [23], the reaction consists of three redox systems characterized by potentials of 4.23, 3.93, and 3.63V with re-... 

Figure 9. Variation of E with the electrochemical density of states (dx/dE) for the solid-state redox reaction of LiNi02. The system described by (dy/d ), which is the sum of the (dx/dE) values, is characterized by three redox systems, (b) Comparison of the observed (O) and calculated E(y) curves for the reaction UNi02 + yLi —> LiyNi02. The E versus y curve was obtained by integrating (dy/dE) in (a) with respect to E from infinity to E.

Transition metal catalysts arc characterized by their redox ehemistry (catalysts can be considered as one electron oxidants/reductants). They may also be categorized by their halogen affinity. While in the initial reports on ATRP (and in most subsequent work) copper266,267 or ruthenium complexes267 were used, a wide range of transition metal complexes have been used as catalysts in ATRP. 

Cyclic voltammetry is most commonly used to investigate the polymerization of a new monomer. Polymerization and film deposition are characterized by increasing peak currents for oxidation of the monomer on successive cycles, and the development of redox waves for the polymer at potentials below the onset of monomer oxidation. A nucleation loop, in which the current on the reverse scan is higher than on the corresponding forward scan, is commonly observed during the first cycle.56,57 These features are all illustrated in Fig. 3 for the polymerization of a substituted pyrrole.58... 

Fig. 2a-c. Kinetic zone diagram for the catalysis at redox modified electrodes a. The kinetic zones are characterized by capital letters R control by rate of mediation reaction, S control by rate of subtrate diffusion, E control by electron diffusion rate, combinations are mixed and borderline cases b. The kinetic parameters on the axes are given in the form of characteristic currents i, current due to exchange reaction, ig current due to electron diffusion, iji current due to substrate diffusion c. The signpost on the left indicates how a position in the diagram will move on changing experimental parameters c% bulk concentration of substrate c, Cq catalyst concentration in the film Dj, Dg diffusion coefficients of substrate and electrons k, rate constant of exchange reaction k distribution coefficient of substrate between film and solution d> film thickness (from ref. 

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