Solid titania structures

The influence of the specific oxide support phase upon the structure and reactivity of the surface vanadia species was also recently investigated.54 A series of titania-supported vanadia catalysts were synthesized over a series of Ti02 supports possessing different phases (anatase, rutile, brookite and B). Raman and solid state vanadium-51 characterization studies revealed that the same surface vanadia species were present in all the different V20/ri02 catalysts54. The reactivity of the surface vanadia species on the different oxide supports was probed by methanol oxidation and the TOFs are shown in Figure 6 (all the catalysts contained 1% V205)... 

It also became evident that a great variety of catalysts, potentially exhibiting a large flexibility, could be prepared via solid solutions. Three different degrees of freedom can be varied in a controlled fashion the chemical nature of the host matrix AO, the chemical nature of the guest cation M, and the dopant concentration x. Furthermore, solid solutions can be formed not only by cubic oxides but also by alumina, titania, zirconia, and others. Thus, another degree of freedom is added, namely, the different crystal structures. 

Supported vanadium catalysts, whereby vanadium oxide is dispersed on a support such as alumina or titania are of particular importance in, for instance, the oxidative dehydrogenation of alkanes [58-64]. Such materials have attracted considerable interest in the direct dehydrogenation of butane, where a key driver is to identify the relationship between catalytic activity and structural properties [5, 6, 65-68]. In the pure (solid) metal oxides the coordination of vanadium is well defined. However, this is not necessarily true in the case of supported catalysts. Vanadium may be present on the support surface as isolated vanadium ions dimeric or polymeric species one- and two-dimensional chains of vanadium ions ... 

Pure titania has the rutile structure and therefore has limited solubility in YSZ. The observed linear decrease in lattice parameter with increasing titania concentration in these solid solutions suggests that titanium cations enter the lattice substitutionally for zirconium. Concordant with the data from XRD measurements [29,30,123] the cubic fluorite structure is retained upon addition of 12-20 mol% titania, above which a second phase appears, claimed to be ZrTi04 [123]. The spread in data of the solubility limit produced by different authors may be due to slight differences in, e.g., yttria concentration, sample processing, sintering temperature and impurity content in the cited studies. Microstructural investigations based on SEM and TEM indicated that precipitates of the second phase actually may appear already at lower titania contents [123,125]. 

In terms of this adsorption, properties of various adsorbents, among them the inorganic sorbents can be determined. It must be emphasized that inorganic sorbents such as silica, alumina, titania, complex carbon - mineral sorbents, apatites, e.t.c., are both structurally and energetically heterogeneous. Their total heterogeneity may be described by the kinds of adsorption potential distribution function which is one of the most significant characteristics of the aforementioned solids. 

The effect of yttria was found particularly strong with silica and alumina and moderate with the other oxides, zirconia and titania. This behaviour may be related to the findings that for the two former doped oxides, only amorphous materials were synthesised before any temperature treatments while in the case of the two latter ones, the solids as obtained exhibited already crystalline structures in the absence of any thermal treatment. 

D. V. Talapin, E. V. Shevchenko, C. B. Murray, A. Kornowski, S. Forster, and H. Weller. Cdse and CdSe/CdS nanorod solids. J. Am. Cherrt Soc., 126 12984-12988, 2004 M. Adachi, Y. Murata, J. Takao, J. T. Jiu, M. Sakamoto, and F. M. Wang. Highly efficient dye-sensitized solar cells with a titania thin-film electrode composed of a network structure of single-crystal-hke Ti02 nanowires made by the oriented attachment mechanism. J. Am. Chem. Soc., 126 14943-14949,2004... 

In pressed disks the particles are held together only by surface forces. Solids that can be easily pressed are silica derivatives (e.g., Cab-O-Sil and Aerosil), a number of oxides (e.g.. Alumina C and Titania P25) and supported metals. Disregarding the technical problems concerning the disk preparation and their mechanical stability, which are discussed by Parkyns and Bradshaw [123], the essential disadvantages of this method for in situ studies are the formation of zones within the pressed matter, which are inaccessible for reaction with the surroundings, and changes in the support structure when the disk is pressed. 

In the case of the MCC/oxide mixtnres, strong interactions of cellulose with the silica or titania surfaces result in decrease in the amounts of bound water. Relative contributions of mesopores decrease (Tables 5.8 and 5.9, and Figure 5.54). This is typical result for soft/solid systems because of the formation core (solid)-shell (soft, nonrigid) structures with the displacement of a significant amount of water, which was bound to both soft and solid surfaces alone. This effect is much lower in the case of solid-solid particles interactions because of the rigid, fixed particle structure of solids. 

Beghi M, Chiurlo P, Costa L, PUadino M, Pirini M F (1992) Structural investigation of the sUica-titania gel/glass transition. J Non-Cryst Solids 145 175-179... 

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