Ti oxides

Hydrogenation. Gas-phase catalytic hydrogenation of succinic anhydride yields y-butyrolactone [96-48-0] (GBL), tetrahydrofiiran [109-99-9] (THF), 1,4-butanediol (BDO), or a mixture of these products, depending on the experimental conditions. Catalysts mentioned in the Hterature include copper chromites with various additives (72), copper—zinc oxides with promoters (73—75), and mthenium (76). The same products are obtained by hquid-phase hydrogenation catalysts used include Pd with various modifiers on various carriers (77—80), Ru on C (81) or Ru complexes (82,83), Rh on C (79), Cu—Co—Mn oxides (84), Co—Ni—Re oxides (85), Cu—Ti oxides (86), Ca—Mo—Ni on diatomaceous earth (87), and Mo—Ba—Re oxides (88). Chemical reduction of succinic anhydride to GBL or THF can be performed with 2-propanol in the presence of Zr02 catalyst (89,90). 

Fig. 1. Logarithmic scale of the electrical conductivities of materials categorized by magnitude and carrier type, ie, ionic and electronic, conductors. The various categories and applications ate given. The wide conductivity range for the different valence/defect states of Ti oxide is highlighted. MHD is...

A third class of catalysts was prepared by electron beam induced deposition of XiCl4 on a polycrystalhne Au foil. Deposition of TiCU at 300 K leads to films which comprise Ti + and Ti species as inferred from XPS measurements [90]. Depending on the experimental parameters (background pressure of TiCU, electron flux, electron energy) different composition of Ti oxidation states are observed [23]. From angular-dependent measurements it was concluded that the Ti + centers are more prominent at the surface of the titanium chloride film, while the Xp+ centers are located in the bulk [90]. 

As for the Ti oxidation state after reduction with alkylaluminum compounds, literature reports are often contradictory, owing to the different catalysts and analytical methods used.108110,113 117 The only reasonable conclusion is that under polymerization conditions a considerable reduction of Ti(IV) takes place, not only to Ti(III) but to Ti(II) as well. However, Ti(II) is usually considered not to be active for propene polymerization.116... 

Figure 10.13 (A) HREEL and (B) Auger electron spectroscopy (AES) spectra for 1.5 monolayer (ML) TO on the Si02(ML)/Mo(112) surface following annealing at various temperatures (a) Si02(ML)/Mo(112), (b) oxidized at 600 K, (c) oxidized at 800 K, (d) annealed at 1200 K, (e) annealed at 1400 K, and (f) 1 ML Ti oxidized at 800 K. (From Chen, M.-S. et al., Surf. Sci., 581, L115-L121,2005. Used with permission from Elsevier Scientific Publishers.)...

Ru(III) chloride (18.2 g, Johnson-Matthey, Mallory Ltd.), Ti(IV) butoxide (45 ml, Aldrich) and 37% HC1 (6 ml) were mixed together to make the coating solution. The Ti electrodes were dipped into this solution and allowed to air-dry and then heated at about 5°C min-1 to 100°C, remaining at this temperature for 15 min to remove the solvent. The temperature was then increased at 10°C min-1 to 440°C in air and maintained at 440°C for 30 min to decompose the Ru/Ti compounds, thus forming the mixed Ru/Ti oxides. Subsequently, the length of the oxide-coated Ti wire was wrapped in Teflon tape, leaving only the cross-sectional end as the WE for immersion in solution. 

The counter-electrode (CE) was a 40 at.% RuC>2 (the remainder being Ti oxide) electrode, having more than 100 times the apparent surface area of the WE. It was positioned inside a Teflon tube to minimise the amount of hydrogen gas that could be released into the cell solution. An Ag/AgCl electrode was employed as the reference electrode (RE) at high temperatures, while a saturated calomel electrode (SCE) generally served as the RE at room temperature. 

Fig. 5.3 Effect of Ru content on Tafel plot of fresh Ru/Ti oxide electrodes in 5M NaCI (pH of approximately 3.5) at room temperature (with IR compensation).

The CV features (Fig. 5.6) of the 40 at.% Ru/Ti oxide electrodes before, during and after deactivation (achieved by current pulsing between 0 and 0.955 A cm-2) were... 

A.C. impedance behaviour of fresh and deactivated Ru/Ti oxide electrodes... 

To further understand and characterise the oxide deactivation process, a.c. impedance studies were carried out, primarily with a 30 at.% Ru/Ti electrode, at various stages during deactivation. These data were compared to those obtained for freshly formed Ru/Ti oxide films, ranging in Ru content from 5 to 40 at.%. Impedance data were collected at the oxide OCP (approximately 0.9 V versus SCE) in fresh NaCI solutions. Under these conditions, no chlorine reactions can occur and the OCP is defined by the equilibria of the redox states on the Ru oxide surface. Deactivation was generally accomplished by square-wave potential cycling, using overpotentials versus the chlorine/chloride potential of 1.59 to — 0.08 V (60 s cycle-1) in 5 M NaCI + 0.1 M HC1 solutions at room temperature. 

It is well recognised [1, 36, 38, 39] that the electrochemical response (that is the a.c. impedance and cyclic voltammetry) of Ru/Ti oxides at the OCP is due to the pseu-docapacitive reaction ... 

Q.cm. This suggests the absence of any build-up of a TiC>2 layer between the Ti substrate and the Ru/Ti oxide coating with the onset of anode deactivation. Furthermore, the similarity of the frequency response of a failed electrode to that of freshly prepared low at.% (c. 5-10 at.%) Ru electrodes at low frequencies, supports the conclusion of the absence of the build-up of a TiC>2 layer with failed electrodes. 

The electrochemical characterisation studies, discussed in the previous section, showed that a 40 at.% Ru electrode, when subjected to extended electrolysis or potential or current cycling in NaCl solutions and when the chlorine overpotential reaches 300-400mV, behaves like a fresh, low at.% Ru (about 5 at.%) electrode. This strongly suggests that Ru losses from the Ru/Ti oxide coating occur during electrolysis. To determine whether or not the Ru losses in failed anodes take place by uniform dissolution across the entire coating or whether only localised surface... 

Figure 10,20 Major element concentrations in effusive products of Boina series plotted as functions of degree of fractional crystallization, based on equation 10.132. I = first discontinuity (transition from olivine-dominated to plagioclase-dominated fractionation) II = second discontinuity (appearance of Fe-Ti oxides) III = third discontinuity (field of Si02 oversaturated trachytes apatite and Mn-oxides precipitate) IV = beginning of peralkalinity field. From Barberi et al. (1975), Journal of Petrology, 16, 22-56. Reproduced with modifications by permission of Oxford University Press.

The Boina emission products show a more or less continuous differentiation trend from transitional basalt to pantellerite. In the nonperalkaline field, the transition from basalt to ferro-basalt is dominated first by olivine F > 0.65) and then by plagioclase F > 0.45), with minor clinopyroxene. A second differentiation step with the appearance of Fe-Ti oxide crystals begins at F = 0.45 Fe and Ti decrease abruptly. Less marked discontinuities are also observed at F = 0.3 (silica-oversaturated trachytes) and F = 0.15 (peralkalinity field). 

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