Cu oxidation

Explds violently on contact with Cu oxide and is friction sensitive. Its Hg salt is also an expl Refs 1) Beil 25, 114 2) D.D. Phillips ... 

With regard to metals or oxides, the violence of reaction depends on concn of the performic acid as well as the scale and proportion of the reactants. The following observations were made (Ref 1) with additions of 2—3 drops of about 90% performic acid. Ni powder becomes violent Hg, colloidal Ag and Th powder readily cause explns. Zn powder causes a violent exp In immediately. Fe powder (and Si) are ineffective alone, but a trace of Mn dioxide promotes deflagration. Ba peroxide, Cu oxide, impure Or trioxide, Ir dioxide, Pb dioxide, Mn dioxide, and V pentoxide all cause violent decompn, sometimes accelerating to expin. Pb oxide, trilead tetraoxlde and Na peroxide all cause an immediate violent expin... 

For oxygen interactions, similar interpretations as for CO can be offered in the chemisorption stage, but the onset of oxidation complicates the SIMS data at high exposures. At very high exposures, it is possible to detect the onset of Cu oxidation by a sudden rise in the, by then, very low Cu+/Ni ratio. 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

The chemical analyses of the samples are reported in Table 2. The X-ray diffraction spectra of these solids do not show the presence of any Cu oxide phase with size larger than 3-4 nm, excepted in the cases of Cu(3)Si02 and Cu(4)Zr02 on one side, Cu(146)Na(6)FAU-10 and Cu(146)Na(28)MFI-15 on the other side, where the lines characteristic of CuO do appear with a line broadening corresponding to a particle size of about 4 nm. 

Maximum temperatures and hydrogen consumption during the temperature programmed reduction of Cu/oxides by hydrogen, and NO taken up by Cu atom. 

Final detennination of the structure was made by proposing a structural model with Cu sitting in threefold hollow sites and O atoms on atop sites with respect to the Cu atoms (Fig. 27.16). A program, FEFFIT, was used to analyze the data (Stem et al., 1995). This calculates the phase and amplitude parameters for the various backscatters. The EXAFS for the parallel polarization could be fitted six Cu-Cu interactions at a bond distance of 2.67 A and three Cu-Pt interactions at 2.6 A. For the perpendicular polarization, the data could be fitted one Cu-0 interaction at 1.96 A and three Cu-Pt interactions at 2.6 A. The Cu-Pt bond length is shorter than the sum of the metallic radii of Cu and Pt, which is 2.66 A. This indicates a Cu oxidation state different from zero, which agrees with the XANES results. 

The low solubility of Cu oxide and hydroxide minerals and relatively high solubility of its carbonate cause the preferred association of Cu with the oxide phases, such as CuFe204j that may determine the solubility of Cu2+ in soil solution (Lindsay, 1979). In soils with high pH, lead carbonate (PbC03 (cerussite)) is stable, but its solubility is still higher than that of Pb phosphates. 

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. 

Alternatively, acrylic acid can be obtained in a two-step reactor in which glycerol is catalytically dehydrated with an acid catalyst like H3PO4 on a-alumina [67]. The obtained acrolein is then oxidized with a commercially available oxidation catalyst, viz. Mo/V/W/Cu-oxide on a-alumina, yielding up 55% polymerization grade acrylic acid (Scheme 11.8) [68]. 

The steady-state voltammogram of PVI-1-coated Cu in 0.1M HClOjj, given in figure 2C, is more complex than that for BTA-coated Cu. On the positive sweep the current becomes anodic at i-45mV (SCE) and as with BTA-coated Cu, the Cu oxidation is inhibited, but to a lesser extent. The initial cathodic currents are enhanced in comparison to bare Cu and BTA-coated Cu, but the limiting oxygen reduction current is close to that for bare Cu. 

All of the inhibitor compounds affected the the Cu oxidation processes in both 0.1M HClOj, and phosphate buffer. The type of effect depended on the pH and the magnitude depended on the inhibitor. In 0.1M HClOj the potential of observed Cu dissolution is shifted in a positive direction. Quantitative measurements were not made but the inhibitors can be ranked in order of decreasing potential shift as follows ... 

The ores are blended with Na2C03 and KNO3, then roasted. Part of the S and As are removed as volatile compounds, leaving Co, Ni, and Cu oxides, with some sulfates, and arsenates. The sulfates and arsenates are leached with HOH, then the oxides are dissolved in hot H2SO4. The solution is treated with the oxidant NaClO, and the hydroxides are selectively precipitated by careful... 

In companion papers (119)(120), M. Arjomand and DJ. Machin presented a comprehensive study on ternary Ni and Cu oxide compounds. In this survey they outlined the preparation and characterization of several ternary oxides containing Cu and Ni ions in their normal, and higher oxidation states. In particular, their data on orthorhombic La2Cu04 suggested antiferromagnetic interactions (they also observed only a low, temperature-independent, magnetic moment in the 80-300 K region). 

This oxygen variation and the Cu oxidation states play a very important role in the superconducting behavior of this compound. For example, the oxygen content (or x vacancy), the copper oxidation states, and the onset temperatures for superconductivity are listed below for different compositions. 

The most heavily studied high temperature superconductor is YBa2Cus07 x (x = 0 to 1), whose Cu oxidation state is determined by the oxygen content. The parent structure, YBa2Cus07, contains layers... 

Ichikawa, Y., Adachi, H., Setsune, K., Hatta, S., Hirochi, K. and Wasa, K., Highly Oriented Superconducting Tl-Ca-Ba-Cu-Oxide Thin Films with 2-1-2-2 Phase, Appl. Phys. Lett. 53 919 (1988). 

Figure 2.8 Redox-driven translocation of a copper center, based on the Cu"/Cu change. The Cu11 ion stays in the tetramine compartment of the ditopic ligand 10, whereas the Cu1 ion prefers to occupy the bis-(2,2 -bipyridine) compartment. The translocation of the copper center between the two compartments is fast and reversible when carried out through the Cun-to-Cu1 reduction with ascorbic acid and Cu -to-Cu" oxidation with H202, in a MeCN solution.

The starting potential has been set at —300 mV (versus Fc + /Fc), where the dinuclear complex is stable (a). On increasing the potential, a poorly defined oxidation peak develops (b), corresponding to the Cu -to-Cu" oxidation process. At 900 mV, the potential is reversed. However, going down to 500 mV and less, the reduction peak opposite to peak b is not observed. In fact, the oxidation to Cu11 is followed by a fast... 

Figure 2.18 A square scheme illustrating the disassembling of the [Cu2(16)2]2 + double helicate complex, following Cu -to-Cu" oxidation, and the consequent assembling of two [Cun(16)]2+ mononuclear complexes, following the Cu"-to-Cu reduction. The process ultimately derives from the geometrical coordinative preferences of the two oxidation states Cu1 prefers a tetrahedral coordination, which can be achieved with the double helicate arrangement Cu11 prefers a square coordination geometry, which is fulfilled by the coordination of a single molecule of 16.

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