Formation from titanium dioxide

The formation of carbon monoxide aids chlorination in exactly the same way as does the formation of carbon dioxide which of the two oxides of carbon would found in the reaction depends on the temperature at which reduction-chlorination is carried out. Below 600 °C carbon dioxide forms while above 700 °C carbon monoxide is formed. This changeover results from the variation in the free energies of formation of these two oxides with temperature. For example, at 900 °C the situation as regards the formation of titanium tetrachloride from titanium dioxide is guided by the reactions ... 

Interfacial hole transfer from titanium dioxide to organic and inorganic solutes has been studied by Grabner et al. [48], Colombo and Bowman [49], and Bahnemann and co-workers [26]. Grabner et al. have shown that in titanium dioxide sols containing chloride (which is either introduced into the solution as HC1 to adjust the pH or is present on the particle surface when TiCU is used as the starting compound to prepare Ti02) Cfe " radical anions are formed. Their formation was postulated to occur by direct valence-band hole oxidation of surface adsorbed Cl" (reactions 19 and 20) [48]. 

Several studies on the formation of self-organized Ti02 nanotube layers [26, 38] have shown that the growth of oxide nanotubes results from a competition between two reactions. The first reaction is the electrochemical formation of titanium dioxide and may be written in two forms ... 

CASRN 108-43-0 molecular formula CeHsClO FW 128.56 Photolytic. Irradiation of an aqueous solution containing 3-chlorophenol and titanium dioxide with UV light (X >340 nm) resulted in the formation of chlorohydroquinone then to hydroxyhydroquinone. Identification of compounds from the oxidation of hydroxyhydroquinone to carbon dioxide were not identified because of the low concentrations (D Oliveira et al, 1990). 

XRD analysis could also provide interesting information regarding the inorganic materials formed during the carbonization process in complex formulations.28,36 As an example, in the case of intumescent coatings, the formation of titanium pyrophosphate resulting from the reaction between APP and titanium dioxide can be demonstrated (Figure 10.17). 

Although the surface models for anatase and rutile, as proposed by different authors, are idealized and differ from each other in details, it can certainly be concluded that coordinatively unsaturated Ti4+cations, O2- ions, and OH groups in widely varying configurations should be exposed on partially hydrated and/or hydroxylated surfaces. Depending on the local environments of these sites, a wide spectrum of possible intermolecular interactions should be the consequence which may render specific adsorption processes possible. Finally, the ease of the surface reduction of titanium dioxides due to hydrocarbon contamination (19) leads to the formation of new types of surface sites and to drastic changes of the surface properties. 

Polyester. The most common polyester in use is derived from the homopolymer poly (ethylene terephthalate). Many types of this fiber contain a delustrant, usually titanium dioxide. Optically brightened polymers are quite common. The optical brightener, such as specially stabilized derivatives of either stilbenes or phenylcoumarins, can be added to the polyester before formation of the fiber (107). Some commercial fibers contain minor amounts of copolymerized modifier to confer such properties as basic dyeability. A wide range of polyester fibers is used for consumer end-uses. Both staple fiber and filament yarn are available. Filament yarns with noncircular cross-sections are made (107). 

The alkyl-, alky laryl- and diarylcarbodiimides are the diimides derived from carbon dioxide, however, no direct formation of carbodiimides from amines and carbon dioxide is known. Interestingly, carbodiimides can be obtained from amines and carbon dioxide via a switteri-onic titanium complex (see Section 2.2.8). The major starting materials for the synthesis of carbodiimides are isocyanates, 1,3-disubstituted ureas or 1,3-disubstituted thioureas. The synthesis of isocyanates requires the use of the toxic carbonyl chloride or its oligomers. A book on the synthesis and reactions of isocyanates appeared in 1996. ... 

The formation of formaldehyde from formic acid is not expected to occur on stoichiometric TiO2(110) because the surface cations are exclusively five-coordinate, and formaldehyde formation in the absence of reduced surface sites has been shown to be dependent on the presence of low-coordinate metal cations on titanium dioxide surfaces. Iwasawa et al. noted the absence of formaldehyde from the product slate of formic acid reaction products in their studies on the TiO2(110) surface [43]. 

If so, one may expect products to result from chemical bond formation between the cation-radical-anion-radical pair, which are both paramagnetic and of opposite charge. In the latter route, there is a precedent for the formation of dioxetane intermediates of stable olefin cation radicals [51], as in the characterization by Nelsen and coworkers of a dioxetane cation radical from adamantylidene cation radical [52]. If a dioxetane is formed, either in neutral form or as a cation radical, the Ti02 surface can function in an additional role, that is, as a Lewis acid catalyst, to induce decomposition of the dioxetane. Since no chemiluminescence could be observed in these reactions, apparently Lewis acid catalysis provides a nonradiative route for cleavage of this high-energy intermediate. That Ti02 can indeed function in this way can be demonstrated by independent synthesis of the dioxetane derived from 1,1-diphenylethylene, which does indeed decompose to benzophenone when it is stirred in the dark on titanium dioxide. 

The involvement of the surface OH groups in the formation of peroxo titanium species has recently been confirmed by experiments performed by Oosawa and Grat-zel using a Ti02 rutile photocatalyst pretreated at different temperatures ranging from 873 to 1273 K (such pretreatments are known to cause a more or less irreversible dehyd-roxylation of titanium dioxide cf. Sect. 2.4). As shown in Fig. 14, the amount of oxygen formed during photolysis of an aqueous silver nitrate solution... 

From Figure 6.16, it is clearly seen that the extraframework gallium oxide generated by demetallation at elevated temperatures in water vapor enhances the activity, and the yield of alkenes is increased, whereas the formation of extraframework titanium dioxide leads to the yield of a large amount of methane in the cracking product. 

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