Activation of Cu

Fig. 3.10 Pourbaix diagram for the Cu + In + Se + H2O system at 25 °C. The stability fields were drawn for activities of Cu(II), Se(IV), and In(III) reactive species equal to 10 M. The diagram was assembled by using the candidate reactions included in Table 3.2. (Kois et al.

Groothaert et al., using operando UV-vis spectroscopy combined with online GC analysis [176] and operando X-ray absorption fine structure (XAFS) [177], presented the first experimental evidence for the formation of the bis( x-oxo)dicopper core in Cu-ZSM-5 and for its key role of intermediate in the sustained high activity of Cu-ZSM-5 in the direct decomposition of NO into N2 and 02. In particular, monitoring the catalytic conversion of NO and N20 above 673 K, they found that the bis( x-oxo)dicopper core is formed by the O abstraction of the intermediate N20 (Figure 4.14). Subsequently,... 

Substrate reactivity was as expected (Arl > ArBr ArCl). In contrast to the Suzuki cross-coupling, however, Cu and Ru clusters were not active in the Heck reactions, and the activity of Cu/Pd clusters was lower than that of pure Pd clusters. Note the higher activity of Pd clusters prepared in situ (row F) compared to pre-prepared clusters (rows B and G). This increased activity tallies with our findings for Suzuki cross-coupling (7). After reaction, palladium black was observed in all the vials in rows B and G, but not in row F. 

Therefore, the high activity of Cu/Si02 in transferring hydrogen from a donor alcohol may be due not only, as already mentioned, to its ability to activate molecular H2, but also to its dehydrogenation activity. 

The extraction equilibrium in the CUPREX process is dependent on the activity of CU in the feed solutions which in turn is dependent on the stability of chlorometallate complexes [MCIJ2 and [MC1X]3 X for the di- and tri-valent metals present149,150, rather than the simple stoichiometry represented by the equation shown in Figure 6.151,152... 

Figure 3 shows polarization curves for the anodic oxidation of H2CO at various metal electrodes recorded by Ohno et al. [38] in a solution maintained at 25 °C and containing EDTA (a commonly used complexant in electroless Cu solutions) and maintained at a pH = 12.5. After exhibiting exceptional activity at potentials less than -0.8 Y (SCE)2, the activity of Cu decreases at ca. 0.3 Y (SCE) this region of activity is more than adequate for electroless deposition of Cu. Although they... 

The catalytic activities of Cu(II), Co(II) and Mn(II) are considerably enhanced by sodium dodecyl sulfate (SDS) in the autoxidation of H2DTBC (51). The maximum catalytic activity was found in the CMC region. It was assumed that the micelles incorporate the catalysts and the short metal-metal distances increase the activity in accordance with the kinetic model discussed above. The concentration of the micelles increases at higher SDS concentrations. Thus, the concentrations of the catalyst and the substrate decrease in the micellar region and, as a consequence, the catalytic reaction becomes slower again. 

Klier and coworkers—Role of ZnO in stabilizing Cu in Cu+ oxidation state, proposed to be the active site. Klier and coworkers235 241 provided a different explanation for the role of zinc in promoting the activity of Cu/ZnO catalysts. They suggested that zinc stabilizes the Cu in the Cu1 + oxidation state, and that it is the Cu ions in the 1 + oxidation state that serve as the active sites. 

Fig. 6.3 Catalytic activity of Cu(II) chelates toward HjOj decomposition. Thi plot illustrates the decrease in catalytic activity with decreasing number of free...

The most important applications of Cu ISEs are in the direct determination of Cu " in water [169, 372,410], complexometric titration of various metal ions using Cu " as an indicator [30, 143,269, 385] and complexometric titrations of Cu " [409]. This ISE has also been used in the determination of the equilibrium activity of Cu in various Cu complexes in order to determine the stability constants (see [46, 285, 317, 318,427, 445]), in the determination of the solubility of poorly soluble salts [122] and in the determination of the standard Gibbs transfer energies [58]. It can also be used in concentrated electrolytes [170]. 

The reversible potential [Eq. (11.1)] of copper in conditions of unit activity for copper ions is 0.34 V, and for zinc ions, 0.77 V. It is clear that if a solution contains unit activities of Cu and Zn ions, zinc will not codeposit with copper unless the overpotential for copper deposition is high enough to compensate for this large difference in deposition p>otentials. 

Sinee water was shown to be a poison for Cu-ZSM-5, it is espeeially important to examine the effeet of water vapor on the activity of Cu-Al-MCM-41 in NO-SCR. A full study is currently undertaken in our laboratory. Figm-e 35 shows the dynamie effeet of introdueing 10% H2O in the feed, on eatalytic activity at 400 °C. The deerease in NO eonversion was sensible but still not very high and by sequential suppression of the water in the gas feed the effect was found to be reversible. The low and reversible deactivation by water vapor during NO-SCR is also signifieant for potential commereial application of these new eatalysts. The surface chemistry of the support, its hydrophilieity, will require investigations before any definitive conclusion can be made. 

Spencer, M.S. Waugh, K.C. Whan D.A. In "The Activity of Cu/ZnO/Al 0 Methanol Synthesis Catalysts" ACS SYMPOSIUM ON METHANOL SYNTHESIS CATALYSTS, Division of Fuel Chemistry American Chemical Society Philadelphia, 1984. 

Fig. 15.13. Activity of Cu nanoparticles in the reaction of dichlorobutene isomerization vs. the dielectric constant of the solvent at different nanoparticle densities.

The importance of zinc for a normal functioning of the Cu-Zn-SOD was shown in Lemna gibba. In zinc-deficient culture media the activity of Cu-Zn-SOD was strongly inhibited whereas in copper-deficient media little change was found in the enzyme activity (Vaughan et al., 1982). In extracts of zinc-deficient plants, restoration of enzyme activity was possible by supplying zinc to the enzyme assay medium. 

From the above reasoning one could expect that the pre-deposition of small amounts of noble metals on the Ti02 surface in a form of the intermediate sub-layer, which can induce the electroactive electronic surface states in the Ti02 band gap, may enhance the electrocatalytic effect of subsequently deposited Cu particles. Actually, the photocatalytic deposition of silver particles in amount of 5xl014 atoms/cm-2, which on its own only slightly increases the electrocatalytic activity of Ti02 electrode, leads to 2-3-fold enhancement of the electrocatalytic activity of Cu particles subsequently deposited in a relatively high concentration (1016-1017 atoms/cm 2) [52],... 

Active sites with peptidase activity were also created on polystyrene backbones with attached metal complexes as the catalytic center. When the Cu(ii) complex of cyden (Cyc) was attached to cross-linked polystyrene, the proteolytic activity of Cu(n)Cyc was enhanced remarkably [49]. By substitution of the chloro groups of PCD with various nucleophiles, PCD derivatives 9 and 10 were prepared. y-Globulin was hydrolyzed effectively upon incubation with 9 and 10. Proteolytic activity of Cu(n)Cyc was enhanced by up to 104-times upon attachment to the polystyrene. Since only a small fraction of Cu(n)Cyc moieties is present on the open surface on PCD and can participate in the hydrolysis of y-globulin, the normalized degree of activation must be substantially greater than 104-fold. Activation of Cu(n)Cyc on the surface of polystyrene was attributed to the hydrophobic environment. 

The Co(m)-complex of cyden, Co(m)Cyc, is one of the most effedive synthetic catalysts discovered so far for the hydrolysis of supercoiled DNAs [59]. The hydrolytic nature of DNA cleavage by the Co(m) complexes of polyamines including cyden has been well documented [57, 58]. The mechanism illustrated in 25 has been proposed [57] for the catalytic action of the Co(m) complexes. Given the remarkable enhancement of proteolytic activity of Cu(n)Cyc upon attachment to PCD [49], we tested the activity of Co(m)Cyc in phosphodiester hydrolysis to see if it is also enhanced greatly upon attachment to PCD derivatives [61, 62]. 

Kasatkin I, Kurr P, Kniep B, Trunschke A, Schlogl R. Role of lattice strain and defects in copper particles on the activity of Cu/ZnO/Al2C>3 catalysts for methanol synthesis. Angewandte Chemie, International Edition. 2007 46(38) 7324-7327. 

The relationship between the PL behavior of Cu(I) species and the photocatalytic activity of Cu(I)/SAPO-5 has been investigated as a function of the Si/Al ratio. The results show that the excited state of Cu(I) species plays a significant role in the photocatalytic decomposition of N2O into N2 and O2. 

Special conditions the above method is valid for a pure enzyme preparation, but cannot give entirely reliable measurements for impure samples. Interfering reactants in the medium may be allowed for by carrying out recovery experiments with a range of amounts of pure SOD added to the test enzyme preparation. Dialysis of the enzyme preparation will eliminate small molecules that may interfere, like ascorbate, reduced glutathione and catecholamines. The addition of 2 //M cyanide may be used to block peroxidases, which has only a minimal effect on the activity of Cu/Zn-SOD. Alternatively 10-5 M azide may be used to block peroxidases without effect on Cu/Zn-SOD. 

FIGURE 7.9 Potential-pH diagrams of Cu-glycine-H20 system at two different activities of Cu at the glycine concentration of 0.1 M (from Ref 55). 

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