Titania comparisons

Figure 2. Comparison of initial rates and selectivities (related to olefin and peroxide) for the epoxidation of a-isophorone with t-butyl hydrojjeroxide at 60 C over (a) low-temperature aerogel (LT) (20 wt% Ti02), (b) titania-on-silica, (c) TS-1 and (d) xerogel.

The comparison of the results of TPR with those of NO TPD on Cu on silica and alumina suggests that a better dispersion of the Cu species induces a higher reducibility of Cu, as reported elsewhere [16]. On the other hand, a strong support effect appears in the case of Cu supported on zirconia or titania, which shows the easiest reducibility in spite of a low dispersion as judged from XRD. 

For Ti02 and Z1O2, it is well known that sulfation induces a strong increase of acidity [17] and the participation of an add mechanism could then account for this promotion of activity. This mechamsm can be described as a bifunctional process oxidation of NO to NO on Cu sites, and nitration of a product of the oxidation of decane on the acid fiinction(8). The preparation of the catalyst must have a great influence on the activity. This has been shown by the comparison of three Cu/TiC catalysts prepared in different conditions one in which titania is first treated with sulfuric acid, then by Cu acetate (denominated Cu 04/Ti02, containing 0.S wt% Cu, 0.6 wt% S), one in which Cu is... 

Figure 16.9 Comparison of cyclic voltammetry in a CO-saturated electrolyte (0.5 M HCIO4) of Au supported on carbon (solid curves) and titania (dashed curves) for four different particle sizes (indicated). The measurements were made at a temperature of 298K and a scan rate of 50mV s ...

It was not until recently that Chen and Goodman probed the influence of the oxide support material on the intrinsic properties at the metal surface. By covering a titania support with one or two flat atomic layers of gold they eliminated, direct adsorbate-support interactions as well as particle size and shape effects. Their results definitively showed that the electronic properties at the metal surface changed due to charge transfer between the support and the metal. Furthermore, their comparison of one- and two-layer films highlighted the dependence of these effects on the thickness of the metal slab. 

S. H. Overbury, L. Ortiz-Soto, H. G. Zhu, B. Lee, M. D. Amiridis, and S. Dai, Comparison of Au catalysts supported on mesoporous titania and silica Investigation of Au particle size effects and metal-support interactions, Catal. Lett. 95(3-4), 99-106 (2004). 

Fig. 5.34 Refractive index variation of 450°C annealed nanotubular titania film, and for comparison a glass (Corning 2947) substrate, in the range 380 to lOSOnm. The Ti02 film has an average refractive index in the visible range of 1.66.

Chen XB, Lou YB, Sarnia ACS, Burda C, Cole JL (2005) Formation of oxynitride as the photocatalytic enhancing site in nitrogen-doped titania nanocatalysts Comparison to a commercial nanopowder. Adv Funct Mater 15 41-49... 

The comparison of the bands observed after benzonitrile and benzylamine transformation over vanadia-titania allows us to suggest that benzamide can also be obtained by oxidation of benzylamine. Moreover, the growth of the absorption near 1640 cm and the appearance of bands at 1330 and 1240 cm during benzylamine oxidation suggests that benzaldehyde is also formed. A likely assignment for the band at 1670 cm is to the stretching of a C=N double bond (75), so being likely indicative of the formation of benzaldimine. 

Figure 13 demonstrates the promotional effect of titania on the activity of Cr/silica catalysts. These samples were made by coprecipitation. The chromium was then added and each sample was calcined at 760°C to form surface attached Cr(VI). For comparison, titania concentrations are expressed as Ti atoms per square nanometer of surface, even though a good part of the titania may actually be in the bulk. 

In all cases, through minor compositional changes, the rr can be adjusted to + a few MK 1. Data for titania and alumina are included for comparison. 

Ceramic and semiconductor thin films have been prepared by a number of methods including chemical vapor deposition (CVD), spray-coating, and sol-gel techniques. In the present work, the sol-gel method was chosen to prepare uniform, thin films of titanium oxides on palladium Titanium oxide was chosen because of its versatility as a support material and also because the sol-gel synthesis of titania films has been clearly described by Takahashi and co-workers (22). The procedure utilized herein follows the work of Takahashi, but is modified to take advantage of the hydrogen permeability of the palladium substrate. Our objective was to develop a reliable procedure for the fabrication of thin titania films on palladium, and then to evaluate the performance of the resulting metalloceramic membranes for hydrogen transport and ethylene hydrogenation for comparison to the pure palladium membrane results. 

Table 1 provides a quick reference to the four key steps in a sol-gel process, the purpose of each step, and the associated experimental parameters that can be varied. Since each of these parameters can potentially affect the properties of a product, literature results on sol-gel preparation should be reported or examined in a similar format to allow a meaningful comparison among different studies. As an example, Tabic 2 shows the parameters used in the preparation of titania [22] and zirconia [26] aerogels. 

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