Oxygen Selectivity

Discussion. One of the most useful titrations involving iodine is that originally developed by Winkler18 to determine the amount of oxygen in samples of water. The dissolved oxygen content is not only important with respect to the species of aquatic life which can survive in the water, but is also a measure of its ability to oxidise organic impurities in the water (see also Section 10.103). Despite the advent of the oxygen-selective electrode (Section 16.36) direct titrations on water samples are still used extensively.19... 

Sample Time (h) Si/M ratio Cyclohexane Conversion (%) TBHP Conversion (%) Mono- oxygenated selectivity (%) Ketone/ Alcohol ratio... 

In contrast to past environmental problems associated with fluorocarbon refrigerants, the exceptional properties of fluorine in polymers have great environmental value. Some fluoropolymers are enabling green technologies such as hydrogen fuel cells for automobiles and oxygen-selective membranes for cleaner diesel combustion. 

So, fullerenes C60 and their derivatives may be potential damaging agents of biologic systems upon PDT, because upon irradiation C60 molecule is able to generate singlet oxygen, selectively penetrate tumor cells, and be accumulated there and could be easily removed from biologic medium. 

A survey of the main routes to convert biomass-derived oxygenates selectively to hydrogen or alkanes over a variety of heterogeneous catalysts has been presented. 

Also of great attractiveness is the direct synthesis of acetic acid from syngas, which would circumvent the two step process of Monsanto. Selectivities of up to 50 % are claimed. An economic analysis by Hoechst A.G. indicates (1/7) that this process is already economically feasible at a 80 % C2 Oxygenate selectivity. 

Deeper oxidation products like furan and, particularly, maleic acid anhydride, can be produced by catalysts that have a stronger oxidative power than the above type-(a) catalysts, but, at the same time, have retained the capacity to transfer oxygen selectively to the organic molecule (a capacity which is absent in the type-(b) catalysts). Besides, a more acidic character of the catalyst surface is probably required to produce an acidic product like maleic anhydride effectively. The most interesting catalysts of this group are V2Os-based catalysts and certain molybdates and Mo03-based catalysts. 

The conversion of toluene to benzene was studied by Steenhof de Jong et al. (302—304), by both pulse and flow experiments. In the absence of oxygen, selectivities of up to 70% are obtained with bismuth uranate catalysts at 400—500° C. The best catalyst is Bi2U06. The catalyst is reduced in the oxidation process, as gas phase oxygen is absent. The reduction proceeds to metallic bismuth and U02. The activity decreases during reduction, but is completely restored by reoxidation with air. Therefore, a regenerative mode of operation is proposed for practical application of this process. 

C.F. Gottzmann, R. Prasad, J.M. Schwartz, V.E. Bergsten, J.E. White, T.J. Mazanec, T.L. Cable and J.C. Fagley, Tube and Shell Reactor with Oxygen Selective Ion Transport Ceramic Reaction Tubes, US Patent 6,139,810 (October, 2000). 

Ion-molecular reactions are used to resolve isobaric interferences, as discussed, in ICP-MS with a collision/reaction cell or by utilizing ion traps. The mass spectra of Sr, Y and Zr (Fig. 6.10a) without O2 admitted into the collision cell and (Fig. 6.10b) with 10 Pa Oj are different. By introducing oxygen, selective formation of YO and ZrO, but not SrO, is observed. This behaviour of different oxide formation is relevant for an interference free determination of Sr. Ultrahigh mass resolving power ICP mass spectrometry (at m/Am 260 000) selectively removes unwanted ions prior to transfer to the FTICR analyzer cell by gas-phase chemical reactions, e.g., for separation of Ca from " Ar+ obtained with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer equipped with a 3 tesla superconducting magnet. ... 

Higher interaction of oxygen molecules with CeX may be explined in terms of interaction of oxygen molecules with non-stochiometric oxides of cerium probably formed inside zeolite cavities due to interaction of cerium with zeolitic firework oxygens. Cerium is known for its non-stochiometric oxides, which are oxygen selective. 

Oxygen transport through the solid state can be caused by the difference in both electrical and chemical potentials. The last effect can be used for the development of oxygen-selective ceramic membranes. The demands of materials for such membranes are similar to the demands for solid electrolytes high density in order to prevent physical penetration of the gas and a high coefficient of oxygen... 

GUr T.M., Belzner A. and Huggins R.A., A new class of oxygen selective chemically driven nonporous ceramic membranes. Part I. A-siie doped perovskites, J. Membr. Sci. 75 151 (1992). 

This set of results suggests that bimetallic carbonyl clusters derived from mixed Fe/Rh cluster complexes yield discrete RhFe atom sites that are active for olefin hydroformylation as well as for successive hydrogenation of these products to alcohols. Enhancement of hydroformylation over simple hydrogenation of olefins on the Fe-containing Rh cluster-derived catalysts results in an appreciable improvement in oxygenate selectivity. 

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