Promotion with oxide ions

Duma and Honicke were the first to report the successful use of N2O in propene epoxidation. A PO yield of 5% was obtained over silica-supported iron oxide catalysts promoted with Na ions [43bj. The pore shape and diameter of the support as well as iron oxide dispersion are crucial parameters in the reaction [43b,cj. Doping vdth alkali metal may also considerably affect the Fe dispersion, and favor epoxidation over allylic oxidation [43fj. Further modification by boron can also significantly enhance the catalytic performance of the K-doped FeO /SBA-lS catalyst [43gj. 

As shown in Figure 12.4 this finely dispersed Pt catalyst can be electrochemically promoted with p values on the order of 3 and A values on the order of 103. The implication is that oxide ions, O2", generated or consumed via polarization at the Au/YSZ/gas three-phase-boundaries migrate (backspillover or spillover) on the gas exposed Au electrode surface and reach the finely dispersed Pt catalyst thereby promoting its catalytic activity. 

The detection and quantification of one or more of the above lipid peroxidation produas (primary and/or secondary) in appropriate biofluids and tissue samples serves to provide indices of lipid peroxidation both in ntro and in vivo. However, it must be stressed that it is absolutely essential to ensure that the products monitored do not arise artifactually, a very difiScult task since parameters such as the availability of catalytic trace metal ions and O2, temperature and exposure to light are all capable of promoting the oxidative deterioration of PUFAs. Indeed, one sensible precaution involves the treatment of samples for analysis with sufficient levels of a chainbreaking antioxidant [for example, butylated hydroxy-toluene (BHT)] immediately after collection to retard or prevent peroxidation occurring during periods of storage or preparation. 

A comparative study of oxides which were closely related, but had different electrical properties, showed that both n- and p-type semiconduction promoted the oxidation reaction, forming CO as the major carbon-containing product. In a gas mixture which was 30% methane, 5% oxygen, and 65% helium, reacted at 1168 K the coupling reactions were best achieved with the electrolyte Lao.9Sro.1YO 1.5 and the /i-lype semiconductor Lao.sSro MntL A and the lily pe semiconductor LaFeo.sNbo.2O1 a produced CO as the major oxidation product (Alcock et al., 1993). The two semiconductors are non-stoichiometric, and the subscript 3 — x varies in value with the oxygen pressure and temperature. Again, it is quite probable that the surface reactions involve the formation of methyl radicals and O- ions. 

A weakening of the critical metal-oxygen bonds occurs as a consequence of the protonation of the oxide ions neighboring a surface metal center and imparting charge to the surface of the mineral lattice. The concentration (activity) of D should reflect that three of such oxide or hydroxide ions have to be protonated. If there is a certain numer of surface-adsorbed (bound) protons whose concentration (mol nr2) is much lower than the density of surface sites, S (mol 2), the probability of finding a metal center surrounded with three protonated oxide or hydroxide ions is proportional to (CJ/S)3. Thus, as has been derived from lattice statistics by Wieland et al. (1988), the activity of D is related to (C )3, and the rate of proton-promoted dissolution, Rh (mol nrr2 lr1), is proportional to the third power of the surface protonation ... 

Molten Carbonate Fuel Cell (MCFC) The electrolyte in this fuel cell is usually a combination of alkali carbonates, which is retained in a ceramic matrix of LiA102. The fuel cell operates at 600 to 700°C where the alkali carbonates form a highly conductive molten salt, with carbonate ions providing ionic conduction. At the high operating temperatures in MCFCs, Ni (anode) and nickel oxide (cathode) are adequate to promote reaction. Noble metals are not required. 

Benzoic Acid. The industrial-scale oxidation of toluene to benzoic acid is carried out with cobalt catalysts.973,978,982 983 The process, a free-radical autoxidation, is significantly promoted by bromide ions.984 Under these conditions bromine atoms rather than alkylperoxy radicals serve as a regenerable source of chain-initiating free radicals. Substantial rate increase can be achieved by the addition of manga-nese(II) ions.984... 

Ammonia present in the sample also contributes to COD. However, in presence of excess free Cl-, it is converted into HH4C1 and is not oxidized. Long chain aliphatic compounds are often difficult to oxidize. A catalyst, Ag2S04, is therefore added to promote such oxidation. Halide ions present in the sample may, however, react with Ag2S04 forming silver halide. Such halide interference may be partially overcome by adding HgS04. 

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