Titanium oxide surfaces

The Raman spectra for the Ti02 sample showed bands at 145, 197, 397, 516, 638 cm characteristic of anatase, and a shoulder at 448 cm", indicating a small portion of rutile. The y-alumina support showed no Raman active modes [5]. The Raman spectra of 7TA, IOTA and 13TA support samples exhibited weak bands due to anatase and the feature of y-alumina. The rutile form was not detected for any mixed support. The Raman spectra also showed a weak band in the 800-900 cm region which is indicative of Ti-O-Ti bonds [7]. Bands in the 950-1000 cm" region were not observed and this suggests that surface titanium oxide species do not contain Ti=0 moieties. Thus it is concluded that Ti02 forms a surface layer on alumina which has a polymeric structure. 

Veneering Investments. These are phosphate bonded and contain finely ground quart2, 2irconium oxide, and/or titanium oxide to produce highly refractory, low expansion dies of fine detail. The dies are formed within impressions taken of teeth that the dentist has prepared in anticipation of covering the front surface with an aesthetic ceramic veneer. Porcelain or ceramic powders are shaped to detail on the dies and these are fired at high (- 1000° C) temperatures to produce the veneers. The veneers are then cemented to the front surface of the previously prepared teeth. 

In general, the stability of titanium oxide surfaces in moist environments is less of a concern than it is for aluminum oxide surfaces. For example, an FPL or PAA oxide on aluminum would be completely converted to hydroxide in less than 5 min after exposure to boiling water, whereas even after 24 h only slight changes such as crystallite formation and reduction in density of the cell structure occur for... 

The initial step of the coupling reaction is the binding of the carbonyl substrate to the titanium surface, and the transfer of an electron to the carbonyl group. The carbonyl group is reduced to a radical species 3, and the titanium is oxidized. Two such ketyl radicals can dimerize to form a pinacolate-like intermediate 4, that is coordinated to titanium. Cleavage of the C—O bonds leads to formation of an alkene 2 and a titanium oxide 5 ... 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

Figure 1 shows AES data for the oxidized titanium surface before and after deposition of 30 X of platinum with the substrate held at 130 K. The platinum thickness was calculated from the attenuation of the oxygen AES signal assuming layered growth of the metal. From the spectra It Is clear that the platinum was sufficient to completely attenuate the underlaying features of the titanium oxide. 

All of these results are consistent with the notion that surface migration of titanium oxide species Is an Important factor that contributes to the suppression of carbon monoxide chemisorption. The H2 chemisorption experiments on 1-2 ML of Ft, where no migration Is observed, strongly Indicate that electronic (bonding) Interactions are also occurring. Thus, for the tltanla system, both electronic Interactions and surface site blocking due to titanium oxide species must be considered In Interpreting SMSI effects. 

The Ti02 (001) surface was cleaned and reduced by cycles of ion bombardment as previously described [3]. The distribution of titanium oxidation states was determined from cxirve fitting the Ti(2p3/2) envelope in x-ray photoelectron spectra [3]. After surface preparation, reaction experiments were conducted in either the TPD or steady state mode. TPD experiments have been described [1]. XPS spectra were also obtained following a saturation exposure of the sample using the same procedure as that for the TPD experiments. After pump down, the crystal was placed under the Mg X-ray source and the Ti(2p), 0(ls), and C(ls) regions were scanned. For steady-state experiments a dosing needle was aligned perpendicular to the axis of the mass spectrometer. It was used to direct a steady beam of methylacetylene (Linde, 95%) at the crystal surface when the sample was placed at the aperture of the mass spectrometer. Steady state reaction experiments were... 

Onishi, H., Fukui, K. and Iwasawa, Y. (1995) Atomic-scale surface structures of TiO2(110) determined by scanning tunneling microscopy A new surface-limited phase of titanium oxide. Bull. Chem. Soc. Jpn., 68, 2447—2458. 

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. 

Fig. 34. Differential heats of adsorption of oxygen at 450°C on the surface of samples of titanium oxide (anatase) which have been previously reduced by carbon monoxide (pco = 70 Torr) at 450°C for 15 hr 67).

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

Lee et al. s study also investigates the hydrophilicity of the heterocatalyst. They mention that the highly acidic surface of the material is more hydrophobic than the pure titanium oxide surface. They theorize that this is because the acidic surface results in fewer adsorbed OH ions and thus a weaker interaction with water. As expected, this increased hydrophobicity leads to an increase in the stability of dispersions of nanoscale powders of this material. Saltiel et al. showed that WOs-coated titanium oxide powders were much more stable than their uncoated counterparts. Even after agglomeration, the agglomerates of the coated powders were more porous than those of pure titanium oxide (the coated powders had a fractal dimension of 1.55 while the pure titanium oxide powders had a fractal dimension of 1.60). 

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