Anatase titania

Titanium Dioxide. The recrystallization of titanium dioxide in a cover-coat glass is very important to the development of thin, highly opaque finish coats. Titania, Ti02, is the primary opacifying agent for white finish coats. Two polymorphic forms of titania, anatase and mtile, may be present in... 

The purpose of the present paper is to offer a contribute to the understanding of the mechanisms of these reactions by using an IR spectroscopic method and well-characterized "monolayer" type vanadia-titania (anatase) as the catalyst. We will focus our paper in particular on the following subjects i) the nature of the activation step of the methyl-aromatic hydrocarbon ii) the mechanism of formation of maleic anhydride as a by-product of o-xylene synthesis iii) the main routes of formation of carbon oxides upon methyl-aromatic oxidation and ammoxidation iv) the nature of the first N-containing intermediates in the ammoxidation routes. 

Catalysts of different V O loadings from 3.5 to 8.0 wt% were prepared by adding requisite amounts of aqueous ammonium meta vanadate solution to calculated amounts of titania (anatase) support. Excess water was evaporated on a water bath and then oven dried at 120°C for 16 h. All the samples were finally calcined at 480°C for 6 h in air. 

The decrease in activity of heterogeneous Wacker catalysts in the oxidation of 1-butene is caused by two processes. The catalyst, based on PdS04 deposited on a vanadium oxide redox layer on a high surface area support material, is reduced under reaction conditions, which leads to an initial drop in activity. When the steady-state activity is reached a further deactivation is observed which is caused by sintering of the vanadium oxide layer. This sintering is very pronounced for 7-alumina-supported catalysts. In titania (anatase)-supported catalysts deactivation is less due to the fact that the vanadium oxide layer is stabilized by the titania support. After the initial decrease, the activity remains stable for more than 700 h. 

In this paper the origins of the difference in stability of catalysts on different support materials are discussed. Catalysts supported on y-alumina and on titania (anatase) have been tested in the oxidation of 1-butene to butanone. Fresh and spent catalysts have been investigated by means of temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to reveal the causes for deactivation. 

Catalysts were prepared on 7-alumina (Akzo, type 000-3P) and titania (anatase) (Rhone-Poulenc, CRS-31), with BET surface areas of269 and 112 m2/g, respectively. Before use, the support materials were calcined at 675 K for 16 h. 

Sclafani, A. and J.M. Herrmann (1998). Influence of metallic silver and of platinum-silver bimetallic deposits on the photocatalytic activity of titania (anatase and rutile) in organic and aqueous media. Journal of Photochemistry and Photobiology A-Chemistry, 113(2), 181-188. 

Besides alkoxides, acetylacetonates are also used as the starting materials for the synthesis of oxides. Titania (anatase) is obtained by decomposition of titanium oxyacetylacetonate (TiO(acac)2) in toluene at 300°C. Similarly solvothermal treatment of Fe(lll) acetylacetonate in toluene yields microcrystalline magnetite. One of the drawbacks of the use of acetylacetonate may be formation of various high boiling point organic by-products via aldol-type condensation of the acetylacetone. Actually more than 50 compounds are detected by gas chromatography-mass spectrometry (GC-MS) analysis of the supernatant of the reaction, some of which are phenolic compounds and are hardly removed from the oxide particles by washing with acetone. ... 

The final membrane thickness was dependent on dipping time and is usually given after calcination at 600°C, resulting in Y-alumina or titania (anatase) membranes. 

Kumar [39] reports a considerably larger thermal stability for titania membranes in the rutile phase instead of the usual anatase form. The effect of the support on thermal stability has been reported by Kumar et al. [40,41]. Pure, non-supported titania (anatase) membranes lose their porosity completely when calcined at 600°C for 8 h, where as the supported titania membrane retained ca 30% porosity at 900°C (8 h). Unsupported titania-(50 wt%)alumina composite membranes retained a porosity of ca 40% at 700°C (8 h), supported ones retained porosity even at 900°C. 

Vedula, R.R. and Spencer, H.G., Adsorption of polyfacrylic acid) on titania (anatase) and zirconia colloids. Colloids Surf., 58, 99, 1991. 

Georgiadou, I. et al.. Preparation and characterization of various titanias (anatase) used as supports for vanadia-supported catalysts, Colloids Surf. A. 98, 155, 1995. 

The XRD pattern of the mix-TiSi sample showed distinct titania anatase peaks due to the Ti02 component, but no XRD detectable peaks of TiOz crystallites (d > 5 nm) were observed for the ALD samples, even above the theoretical monolayer coverage of 5.5 Ti atoms/nm upport [4,10]. The deposition of highly dispersed titania only caused intensity masking of the broad amorphous line of silica centered at 29 = 23° [10], Nevertheless,... 

Catalysts employed in the oxidative production of PA are V205-based compositions which are generally of the monolayer type and are supported on titania (anatase). With such catalysts, selectivities in excess of 80 mole % PA are achieved at essentially complete conversion. The utilization of Sb-V-oxidc-based catalysts supported on anatase improves the PA selectivity. However, little is known about the intrinsic chemical or electronic effects of Sb203 in such catalytic systems, as well as the chemical and physical characterization of the supported Sb-oxide or supported Sb-V-mixed metal oxide [1]. 

The commercially available catalytic processes for NOx abatement involve the use of transition metal ions such as Cu etc. on a titania (anatase) or zeolite support. The metal... 

Zeolite based catalysts have also been extensively studied for SCR reaction. Zeolite based catalysts are in operation in several chemical process industries (4). Copper loaded zeolites have been reported as excellent SCR catalysts with a wide temperature window particularly for nitric acid tail gas plants. This paper describes the performance evaluation studies and ESR characterisation data on the conventional titania anatase based catalyst and a less common system, viz. vanadyl exchanged mordenite. 

Hydroxyapatite/titania layers were spin-coated on the surface of TiZr alloy at a speed of 3000 r.p.m. for 15 s, followed by a heat treatment at 600 °C for 20 min in an argon atmosphere (Wen et al., 2007). The coating displayed excellent bioactivity when soaked in a SBF for an appropriate period. Differential scanning calorimetry, TGA, XRD and SEM in conjunction with energy dispersive spectroscopy were used to characterise the phase transformations and the surface structures and to assess the in vitro tests. The titania (anatase) layer exhibited a cracked surface and the HAp layer showed a uniform dense structure. Both layers were about 25 im thick. 

Methylpyridines are easily converted into the corresponding nitriles. The ammoxidation of 3-methylpyridine to nicotinonitrile has been particularly extensively investigated, mainly because of the importance of the nitrile as precursor of vitamins. The catalysts used are mostly vanadium-containing oxides, e. g. vanadium-titanium oxide [86], vanadium-zirconium oxide [87], or multicomponent systems [30,88]. Yields of more than 90% at nearly complete conversion were recently reported (e. g. 100% selectivity for vanadium oxide on titania (anatase) catalysts with V2O5 loading < 3.4 mol% [89]. 

Similar templates with solvent swehing properties have been used for nanoparticle infiltration [10]. The acryfic acid/2-hydroxyethylmethacrylate copolymer was soaked in a colloidal sol of 4.5 wt%, 8 nm titania anatase particles for 7 weeks. Thermal treatment to remove the organic scaffold and induce condensation of surface hydroxyl groups between contacting nanoparticles, gave porous titania monoliths. 

Although the amount of solar light that can be absorbed by Ti02 is limited by a band gap of about 3.2 eV, nanotubular titania (anatase and rutile) structures display interesting properties with respect to the photocleavage of water. First, due to light scattering within a porous structure, incident photons are more effectively absorbed than from a flat electrode second, and more important, compared to nanocrystalline electrodes made of sintered nanometer sized... 

AG values are nonlinear functions of the titania content because of several effects caused by textural changes of the materials and the formation of new phases (amorphous titania, anatase, and rutile) with particles of different sizes formed in pores and at the outer surface of the silica gel particles. Water becomes more strongly bound with increasing titania content (Figure 2.73). However, the AG(C J curves for all the SGT samples are above the curve for silica gel. The secondary porosity of silica gel decreases due to grafting of titania, and the peak intensity at / =40 nm of textural pores decreases (Figure 2.74), but a peak at / = 30 nm appears because of partial filling of these broad pores by titania nanoparticles. 

Fig.l shows the pore size distributions of y-alumina, titania (anatase) and tetragonal zirconia (after calcination at 450°C for 3 hours). The pore structure data of these three adsorbent samples are compared in Table 2. The pore structure data were obtained from nitrogen adsorption isotherms measured by Micromeritics ASAP-2000 adsorption porosimeter. As shown in Fig.l, the pore size distributions of these materials are rather narrow, with an average pore diameter of about 3 nm. Such narrow size distribution and nanoscale average pore size are determined by the primary crystallite particles. The particles of the... 

Wachs, L, Saleh, R., Chan, S., et al. (1985). The Interaction of Vanadium Pentoxide with Titania (Anatase) Part I. Effect on o-Xylene Oxidation to Phthahc Anhydride, Appl. Catal., 15, pp. 339-352. 

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