Rotating catalytic disc

Equations (95) and (96) are actually special cases of eqns. (61) and (62) in Sect. 1.6.3. At a rotating disc catalyst, W and the two L values are directly proportional to the square root of the disc rotation speed so that vcat will vary directly with s[f. In contrast, the potential Eat taken up by the catalytic disc, which is equal to Emix on the electrochemical model, will be completely independent of rotation speed. Addition of either of the products Red2 and Ox, to the reaction mixture brings about a dramatic change in the rate law [238], A catalytic system that behaves in this way is reviewed in Sect. 4.4. 

Comparison of the predicted and observed kinetics not only with respect to reaction orders but also with respect to hydrodynamic flow (rotation speed of catalytic disc). Moreover, judicious changes in the experimental conditions should alter the rate equations in a predictable way. In case (c), for example, addition of one of the products should alter the reaction orders of the reactants. In most cases, lowering the concentration of one of the reactants should bring about compliance with case (d). 

Figure 4-9. Catalytic voltammetry of the membrane-extrinsic subcomplex fl/.) of mitochondrial NADH-ubiquinone oxidoreductase adsorbed at a rotating PGE disc electrode in the presence of 1 mM NA I ) and 1 mM NADH at pH 7.8, 20 °C. Reprinted from ref. 56 with permission.

Oxygen electro-reduction and evolution reaction/ cyclic voltammetry, rotating ring disc electrode (RRDE) Ni.Al,, Mn204 KOH solution Two preparation methods are used coprecipitation of metal hydroxides and sol-gel route using metal propionates were used. A Teflon-bound electrode technique was chosen with graphite addition The substitution of Al, by Ni increases the catalytic activity. Maximum activity is experienced by NiMn204 Ponce et al. (2001)... 

Recently, a numerical solution has been obtained for the LSV response to a homogeneous catalytic reaction at an electroactive-monolayer-film-covered rotating disc electrode [279]. 

Lund reported the major product of the reduction of 2- and 4-acid 56 to be the aldehydes 41 and 42, respectively94 a recent report confirmed these results in the case of 2-(56).95 Somewhat contrary to these citations, Brown et al. indicated that the 2-aldehyde (41) was formed in low yield and that with acetate buffer the major product was carbinol 29.96 When rotating disc electrodes were used, the reduction products of 2- and 4-(56) were the aldehydes, but 3-(56) gave only catalytic hydrogen evolution.97... 

Unfortunately, the to-electrode precipitation required for conventional (photo)electrochemical measurements on colloidal semiconductors necessarily perturbs the (assumed) spherical diffusion fields and surface adsorption equilibria that obtain at particles in the free solution state, phenomena which are instrumental in determining the dynamic and static charge transfer characteristics of the semiconductor. Consequently, there is a requirement for photoelectrochemical techniques capable of in situ, non-per-turbative investigations of the mechanistic details and catalytic properties of colloidal semiconductors in solution conditions typical of their intended ultimate application. Two such techniques are photoelectrophoresis and the Optical Rotating Disc Electrode (ORDE, developed by Albery et al.). As mentioned above, the former technique has already been reviewed by this author elsewhere [47]. Thus, the remainder of this review will concentrate on measurements that can be made with the latter... 

Fig. 24. Variation of the initial catalytic rate (O) and the catalyst potential ( x ) with the square root of the platinum disc rotation speed in a reaction mixture containing 1 10 1 mol dm 3 K3Fe(CN)6, 0.05 mol dm 3 KI, and lmol dm a KNOa at 5°C. (After Freund and Spiro [6].)...

Figure 4-1. Protein film voltammetry as a technique for studying redox enzyme mechanisms. The catalytic current-potential profile provides information on the rate-defining catalytic processes occurring within the enzyme. It is important that interfacial electron transfer is facile and information is not masked by limitations due to tlie transport of substrate and product for this reason the rotating disc electrode is an important tool in these studies.

Also, in the case of the reduction of benzofuroxan [59] the UPD adlayers of Pb, Tl, and Bi strongly modify the catalytic activity and selectivity of the platinum electrode. Figure 5 shows the rotating-disc voltammograms for benzofuroxan reduction on Pt and Pt/M(upd), M = Pb, Tl, Bi. 

In steady-state voltammetry experiments, enzyme activity is viewed in the potential domain that can pinpoint the role of centers as electron relays, or reveal the presence of internal control mechanisms, such as a redox transformation that causes the enzyme to switch ofF at a certain potential. Such studies can also reveal and quantify how an enzyme is redox-biased to favor catalysis in a particular direction. Figure 6(b) shows the voltammetry of a film of fumarate reductase obtained in the presence of a low concentration of fumarate and a high concentration of succinate, from which it is easily seen how the catalytic activity of the enzyme is biased heavily in the direction of fumarate reduction [38]. This experiment has been carried out with a rotating disc electrode. The current for succinate oxidation is independent of rotation rate, while that for fumarate reduction is very sensitive because the reaction is diffusion controlled. 

Notes LSV linear sweep voltammetry. CV cyclic voltammetry, DCP direct current polarogra-phy, MEV steady-state voltammetry at microelectrodes, ChP chronopotentiometry, RDE rotating disc electrode, TEV voltammetry in tubular electrodes, kf and k, rate constants of irreversible follow-up and catalytic reactions, respectively cj, the bulk concentration of the catalyst Z k = kf + k, sum of the rate constants and drop time and transition time, respectively a radius of a hemispherical microelectrode, Xf length of the tubular electrode in the flow direction, co the angular rotation rate, Uf linear flow rate in a TE (7 = RT/(nFv) is the time required for the dimensionless potential shift nFdE/RT at the sweep rate v (Vs" ). 

The mechanism of oxidation of D-glucose in alkaline media at gold electrodes has been investigated. Experiments using cyclic voltammetry at a rotating disc electrode indicated that the mass-transport-limited reaction proceeds an enediol intermediate hydrogen-bonded to catalytic hydrous gold oxide. The enediol is... 

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