Titanium dioxide-activated

Direct ammonolysis involving dehydratioa catalysts is geaerahy ma at higher temperatures (300—500°C) and at about the same pressure as reductive ammonolysis. Many catalysts are active, including aluminas, siUca, titanium dioxide [13463-67-7], and aluminum phosphate [7784-30-7] (41—43). Yields are acceptable (>80%), and coking and nitrile formation are negligible. However, Htfle control is possible over the composition of the mixture of primary and secondary amines that can be obtained. 

By quenching the polymerization with C1402 or Cl40 the determination of the number of propagation rate constants was found to be also possible for the two-component catalytic system TiCl2 + AlEt2Cl 158, 159). In contrast to alcohols, carbon dioxide and carbon monoxide under polymerization conditions react only with titanium-carbon active bonds and do not react with inactive aluminum-polymer bonds. 

Taking titanium dioxide as an example, we may mention that PMC transients decay rapidly in the rutile phase (10"6 s) and much slower in the (catalytically more active) anatase phase (10"2-1 s).35 When a Ti02... 

Hydrothermal synthesis of titanium dioxides using acidic and basic peptizing agents and their photocatalytic activity on the decomposition of orange II... 

We have developed a compact photocatalytic reactor [1], which enables efficient decomposition of organic carbons in a gas or a liquid phase, incorporating a flexible and light-dispersive wire-net coated with titanium dioxide. Ethylene was selected as a model compound which would rot plants in sealed space when emitted. Effects of the titanium dioxide loading, the ethylene concentration, and the humidity were examined in batches. Kinetic analysis elucidated that the surface reaction of adsorbed ethylene could be regarded as a controlling step under the experimental conditions studied, assuming the competitive adsorption of ethylene and water molecules on the same active site. 

The photocatalytic activity of 20mesh wire-net photocatalyst was observed to be nearly equal to that of 350mesh one under the same amount of titanium dioxide loading (1.88 g). 

Titanium dioxide supported gold catalysts exhibit excellent activity for CO oxidation even at temperatures as low as 90 K [1]. The key is the high dispersion of the nanostructured gold particles over the semiconducting Ti02 support. The potential applications of ambient temperature CO oxidation catalysts include air purifier, gas sensor and fuel cell [2]. This work investigates the effects of ozone pretreatment on the performance of Au/Ti02 for CO oxidation. 

All commercial materials are based on calcium hydroxide and liquid alkyl salicylates (Prosser, Grolfman Wilson, 1982) and are supplied as a two-paste pack. Zinc oxide is sometimes added to the calcium hydroxide, as are neutral fillers. A paste is formed from this powder by the addition of a plasticizer examples include A-ethyl toluenesulphonamide (o- orp-) and paraffin oil, with sometimes minor additions of polypropylene glycol. The other paste is based on an alkyl salicylate as the active constituent containing an inorganic filler such as titanium dioxide, calcium sulphate, calcium tungstate or barium sulphate. Alkyl salicylates used include methyl salicylate, isobutyl salicylate, and 1-methyl trimethylene disalicylate. An example of one commercial material, Dycal, is given in Table 9.7, but its composition has been subjected to change over the years. 

Titanium dioxide is a catalytically inactive but rather corrosion-resistant material. Ruthenium dioxide is one of the few oxides having metal-like conductivity. It is catalytically quite active toward oygen and chlorine evolution. However, its chemical stability is limited, and it dissolves anodically at potentials of 1.50 to 1.55 V (RHE) with appreciable rates. A layer of mixed titanium and ruthenium dioxides containing 1-2 mg/cm of the precious metal has entirely unique properties in terms of its activity and selectivity toward chlorine evolution and in terms of its stability. With a working current density in chlorine evolution of 20 to 50mA/cm, the service life of such anodes is several years (up to eight years). 

Zhou et al. obtained nitrogen-doped titanium dioxide replicas via a two-step infiltration process with natural leaves as templates [220]. The replicas inherited the hierarchical structures of the natural leaf at the macro-, micro-, and nanoscales. These materials showed enhanced light-harvesting and photocatalytic hydrogen evolution activities. The photocatalytic water splitting activity of the artificial leaf structures was eight times higher than that of titanium dioxide synthesized without templates. 

Shiraishi, Y., Saito, N., and Hirai, T. (2005) Adsorption-driven photocatalytic activity of mesoporous titanium dioxide. Journal of the American Chemical Society, 127 (37), 12820-12822. 

Shiraishi, Y., Sugano, Y., Inoue, D., and Hirai, T. (2009) Effect of substrate polarity on photocatalytic activity of titanium dioxide particles embedded in mesoporous silica. Journal of Catalysis, 264 (2), 175-182. 

Pillai, U.R. and Sahle-Demessie, E. (2002) Selective oxidation of alcohols in gas phase using light-activated titanium dioxide. Journal of Catalysis, 211 (2), 434—444. 

There are three crystal structures of titanium dioxide rutile, anatase, and brookite. The most active phase is rutile, which has a tetragonal structure [133], as shown in Figure 8.5 [134],... 

Heat-flow calorimetry may be used also to detect the surface modifications which occur very frequently when a freshly prepared catalyst contacts the reaction mixture. Reduction of titanium oxide at 450°C by carbon monoxide for 15 hr, for instance, enhances the catalytic activity of the solid for the oxidation of carbon monoxide at 450°C (84) and creates very active sites with respect to oxygen. The differential heats of adsorption of oxygen at 450°C on the surface of reduced titanium dioxide (anatase) have been measured with a high-temperature Calvet calorimeter (67). The results of two separate experiments on different samples are presented on Fig. 34 in order to show the reproducibility of the determination of differential heats and of the sample preparation. 

Panagiotopoulou, P., Christodoulakis, A., Kondarides, D.I., and Boghosian, S. 2006. Particle size effects on the reducibility of titanium dioxide and its relation to the water-gas shift activity of Pt/Ti02 catalysts. J. Catal. 240 114—25. 

To be used as photocatalysts, especially in the so-called clean technologies, active materials must fulfill the following requirements (1) very low toxicity, (2) resistance to photo-corrosion, (3) high availability, (4) high catalytic efficiency, and (5) low cost. From all the materials cited above, titanium dioxide and its derivatives seem to offer the best answer to these requirements, being by far the most commonly utilized photocatalysts. To be used in gas-phase photocatalysis, in addition to the above requirements, two other conditions are still necessary, that is, a very small pressure drop and an easy recovery. 

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