Reduction peaks

In the reductive regime, a strong, apparently irreversible, reduction peak is observed, located at -1510 mV vs. the quasi reference electrode used in this system. With in situ STM, a certain influence of the tip on the electrodeposition process was observed. The tip was therefore retracted, the electrode potential was set to -2000 mV, and after two hours the tip was reapproached. The surface topography that we obtained is presented in Figure 6.2-14. 

For multielectron-transfer (reversible) processes, the cyclic voltammogram consists of several distinct peaks if the E° values for the individual steps are successively higher and are well separated. An example of such a mechanism is the six-step reduction of the fullerenes C60 and C70 to yield the hexaanion products and C7q. Such six successive reduction peaks are observed in Figure 2-4. 

Thus, 9,10-diphenylanthracene ( p = — 1.83 V vs. SCE) is reduced at too positive a potential and hence its rate of reaction with the sulphonyl moieties is too low. On the other hand, pyrene (Ep = — 2.04 V) has a too negative reduction potential and exchanges electrons rapidly both with allylic and unactivated benzenesulphonyl moieties. Finally, anthracene Ev = —1.92 V) appears to be a suitable choice, as illustrated in Figure 3 (curves a-d). Using increasing concentrations of the disulphone 17b, the second reduction peak of XRY behaves normally and gives no indication of a fast electron transfer from A. 

The second approach, followed by Vayenas et al39 is direct measurement of Ntpb and N n using cyclic voltammetry, as in aqueous electrochemistry,49 and measuring the height, Ip, or the area fldt of the cathodic oxygen reduction peak (Fig. 5.28a). Then Ntpb can be estimated from ... 

In the Lai.,CsxMn03 catalyst, the T decreases with an increase of x value and shows an almost constant value upon substitution of x>0.3. It is thought that the oxygen vacancy sites of perovskite oxide increase with an increase of amount of Cs and the oxidation activity also increases. This result is also verified by the TPR result of these catalysts(Fig. 3). As shown in Fig. 3, the reduction peak appears at low temperature with an increase of x value and no change is shown at more than x=0.3. It can thus be concluded that the catalytic performance of these oxides increases as the amount of Cs in the crystal lattice increases. However, the substitution of Cs to more than x=0.3 leads to excess Cs, which is present on the surface of mixed oxides might have no effect on the catalytic activity... 

The introduction of a Pt function influences weakly the behavior of the two high-temperature reduction peaks, but markedly decreases the temperature of the minor low-temperature reduction step from 700 K to 350 K (Figure 5b). These data suggest that some reduction of WOx-Zr02 species can occur during n-alkane isomerization reactions (440-500 K). These reducible W species may act as redox sites required for the conversion of H-atoms to H species on WOx-based solid acids. 

In the case of zeolites (Table 4), a very broad reduction peak is observed on the sample partially exchanged, with a poorly defined maximum. On the other hand, two reduction peaks appear for Cu exchanges higher than 100%. In both cases, however, the consumption of hydrogen corresponds to the reduction of Cu + to metallic Cu. A similar situation was previously reported for Cu-MOR [6]. By... 

The effect of sulfur addition on the TPR profiles for some of these catalysts is reported in Table 5. The saturation of the solid by SO2 shifts the TPR profiles to higher temperatures and a second reduction peak appears at high temperature. The maximum temperatures measured for this second high temperature peak are reported in Table 5 (column 6). The effect of sulfur addition depiends on the nature of the support, and zeolites appear less sensitive to SO2. 

TPR experiments were performed at different amounts of sulfur on a Cu/Zr02 (Fig. 2). SO2 addition induces a modification of the TPR profile the reduction peaks are shifted toward higher temperatures. The total hydrogen consumption is decreased by 50% for the Qrst SO2 dose, then remains constant. 

The electrochemistry of the complex [NBu4][Au(C6F5)2] shows that the reduction peak is <—2.6 V [77]. 

As we will show later in this chapter, the most important anionic derivative, judged by its stability and reactivity is NBu4[Au(C6F5)2], prepared by a one pot synthesis from AuCl(tht)], LiC Fs and [NBu4]Br. It is a very nice reaction which affords beautiful colorless crystals in very good yield. The electrochemistry of the complex NBU4 [Au(C6F5)2] shows that the reduction peak is <—2.6 V [77]... 

Figure 5.6 shows a typical CV of a thin Pt film electrode in a 0.1 M HCIO4 solution. The hydrogen waves in the potential range between —200 and about 50 mV were observed and surface oxidation and reduction peaks were observed in the positive potential region (>600 mV). This result confirmed that the conductivity of the Pt thin film was good enough to be used as an electrode. 

In the cyclic voltammetry, the oxidation peaks of PH were clearly observed in positive scans for all the modified electrodes. In contrast, reduction peaks of Cgo were clearly observed in the absence of magnetic processing but not in the presence of magnetic processing. 

The reductive coupling of allyl halides to 1,5-hexadiene at glassy C electrodes was catalyzed by tris(2, 2,-bipyridyl)cobalt(II) and tris(4,4 -dimethyl-2, 2/-bipyridyl)cobalt(II) in aqueous solutions of 0.1 M sodium dodecylsulfate (SDS) or 0.1 M cetyltrimethylammonium bromide (CTAB).48 An organocobalt(I) intermediate was observed by its separate voltammetric reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene... 

Figure 1 shows cyclic voltammograms in these two solutions. A reduction current is observed with two reduction peaks in the oxygen-saturated electrolyte. In the argon-saturated electrolyte, a single reduction peak at lower current density is observed. From the difference between the reduction currents in the two solutions, the reduction current in the... 

The above experimental data (Figs. 1 and 2) allow us to estimate the possibility for taking place the oxygen reduction process on PANI catalyst. If the special procedure is not taken to withdraw oxygen out of solution, PANI electrode in 1 M HC1 usually demonstrates a potential of about 0.6 V (SHE). In compliance with the Fig. 1 the position of the reduction peak might be at 0. 28 V. From the data of the standard potentials for the following reaction ... 

H2 TPR measurements are used to probe the reducibility and may reveal more information on the nature of vanadium and molybdenum species. The assignment of the TPR peaks has been based on the literature study [9, 10] but also by using two reference samples V1-Z15 and Mol-Z15 prepared by solid-state ion exchange. TPR thermograms of V-Mo-Zeolite systems can be divided into two zones of H2 consumption (/) Mo-Zeolites exhibit two reduction peaks at 600 and 850°C corresponding to the reduction of Mo6+ into Mo4+ through the Mo5+ step and to the reduction of Mo4+ into Mo°, respectively while (ii) V-Zeolites led to a broad asymmetric feature around 710°C, which has been previously attributed to the reduction of V5+ into V3+. Finally, the TPR profiles of V-Mo-Zeolite catalysts seem more like a superposition of both Mo and V-catalysts TPR profiles. 

Figure 1 shows the H2-TPR profiles of Co- and Co/Pd-HFER catalysts. The H2-TPR profile of Co-HFER shows the presence of two peaks at 340 °C and 670 °C corresponding to the reduction peaks of particles of cobalt oxides (Co304 and CoOx respectively). Normally, Co304 are on the external surface while CoOx is inside the zeolite cavities [11-13], At 960 °C, the reduction of the cationic species Co2+ occurs [14]. 

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