Sulfated titania

Preparation effects on titania-sulfate aerogel morphology... 

The presence of sulfate ions markedly affects the nanopore structure of titania-sulfate aerogels. In Ti02-S042 materials, unlike in zirconia-sulfate aerogels, the larger sulfate load stimulates formation of a more consolidated structure. The XRD analysis shows that even a crystalline phase (anatase) may be present in fresh, dry aerogels, which, perhaps, is the first observation of this phase in sol-gel titania obtained from the low temperature drying process. 

The sulfate promoted transition metal oxides focussed considerable attention in recent years due to attractive catalytic properties. Most of the research carried out to date centered on sulfated zirconias,1 5 not surprisingly perhaps, as they exhibit the highest surface acidity (Ho <-16.04) among the members of this family of materials and appear to be able to initiate isomerization reactions in temperatures as low as 298 K. Far less interest attracted sulfated porous titanias, mainly owing to a lower surface acidity,6 although it may be a useful property in many catalytic situations. Thus closer inspection of the preparation procedures for sulfated titanias may be of interest, in particular as the reports on preparation and properties of these materials are scarce and we are not familiar with any work dealing with titania-sulfate aerogels. 

Figure 1. t-plots analysis of titania-sulfate aerogels (( ) points taken for linear regrresion)... 

Figure 2. Pore size distributions in titania-sulfate aerogels before (a) and after calcination (b).

Figure 4. Scattering spectra for titania-sulfate samples before (a) and after calcination (b). To separate the curves, intensities for the samples A15, A20, A20Pt and B20 were shifted upward.

Preparation Effects on Titania-sulfate Aerogel Morphology 467... 

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... 

Out of the metal oxides, sulfated titania and tin oxide performed slightly better than the sulfated zirconia (SZ) catalyst and niobic acid (Nb205). However, SZ is cheaper and readily available on an industrial scale. Moreover, it is already applied in several industrial processes (7,8). Zirconia can be modified with sulfate ions to form a superacidic catalyst, depending on the treatment conditions (11-16). In our experiments, SZ showed high activity and selectivity for the esterification of fatty acids with a variety of alcohols, from 2-ethylhexanol to methanol. Increasing... 

H-ZSM-5, Y and Beta) Sulfated metal oxides (zirconia, titania, tin oxide) Niobic acid (Nb205)... 

Blumenfeld An early version of the Sulfate process for making titanium dioxide pigment, in which the nucleation of the precipitation of titania hydrate is accomplished by dilution under controlled conditions. Invented by J. Blumenfeld, a Russian working in London in the... 

Scratch resistance depends on the hardness of the added particles. The problem of a lack of this property can be addressed by adding chemically identical particles of different crystal modification and Mohs hardness. The preferred additives are silica, alumina, layered silicates such as kaolin, titania, barium sulfate and calcium carbonate. The latter is only suitable for the DMT process owing to side reaction caused by acidity during the terephthalic acid (TPA) route. 

Y. Y. Huang, B. Y. Zhao, and Y. C. Xie, A novel way to prepare silica supported sulfated titania,... 

Another source of error in the investigation of the surface properties of titanium dioxide is its tendency to adsorb acids or ions. Phosphate ions are very strongly adsorbed (see Table XIX) as well as sulfuric acid. Commercial pigments often have considerable sulfate contents. When titania is precipitated from sulfate solution, sulfate ions are strongly adsorbed (308). They are carried through all further stages of pigment manufacture. 

Also for this reaction, namely esterification plus transesterification, mixed oxides, this time acidic in nature, appear to be the most promising alternative. Tungstated zirconia-alumina (WZA), sulfated zirconia-alumina and sulfated tin oxide were shown to be active in the transesterification of soybean oil with methanol at 200-300 °C and in the esterification of n-octanoic acid with methanol at 175-200 °C. Although the order of activities is different for the two reactions, WZA gives high conversions in both readions and it is stable under the reaction conditions [31]. Titania on zirconia, alumina on zirconia and zirconia on alumina also showed good performances [32, 6]. 

Phosphates and sulfates correspond to chemical groups which are difficult to photodegrade due to the fact that they adsorb strongly on semiconductor surfaces, particularly titania, even at concentrations as low as 1 mM. In the case of phosphates, the binding with the oxide is so strong that removal with water is inefficient and alkali washing is necessary. Phosphates and sulfates may, however, display singular features as they form reactive species under UV illumination in accordance with eqns (4) and (5) ... 

In this work, the performance of two green acid catalysts, a Ti02 synthesized by the sol-gel method and sulfated in situ was compared with a traditional NiY zeolite in the trimerization of isobutene. The reaction was carried out at mild conditions atmospheric pressure and 40°C of temperature. The results obtained in the catalytic evaluation showed higher conversion and stability as well as a better selectivity to tri-isobutylene for the sulfated titania catalyst with respect to the NiY zeolite. 

Silica has been used both as a core and shell material. For example, monodis-persed silica spheres were coated with titania by decomposing titanyl sulfate, TiOS04, in acidic solutions at 90°C (146). The particles so produced showed good hiding power, to be useful as paper whiteners (147). Due to the uniformity of the cores and shells, the optical properties of such dispersions were predictable and reproducible, as shown in Figure 1.1.22, which compares the scattering coefficient,... 

Thus the presence of a large sulfate content in a sol-gel system with titania precursors stimulates the formation of a short-range arrangement with trace of anatase. This contrasts with the effect of sulfate on morphology of sol-gel zirconia where the opposite trend was observed.4-5 As expected, all calcined samples proved to be partly crystalline. Diffraction spectra from all calcined samples appeared to be quite similar and showed the presence of very small crystallites of anatase phase (cf. Fig. 5). 

The results obtained clearly demonstrate that sulfate ions promote the consolidation of titania morphology in nanometer scales and the formation of a crystalline, anatase phase in aerogels dried using supercritical carbon dioxide. This trend is consistently demonstrated by adsorption experiments as well as SAXS and XRD studies. The presence of platinum promotes the formation of a fine polymeric structure of titania in nanometric scales. After calcination all samples exhibit a similar morphology, yet with a notable difference in texture parameters. 

Cr/alumina can be modified like Cr/silica. Adding titania is not particularly useful, but replacing the hydroxyls with fluoride does boost the activity by as much as 10-fold (62). An example is shown in Fig. 22, where activity is plotted versus the amount of fluoride impregnated onto a highly porous alumina. Too much fluoride tends to sinter the alumina and destroy the activity. Other modifications which improve the activity of Cr/alumina include adding chloride, sulfate, boria, phosphate, or 1-5% silica (62, 78). 

Saur and others studied the structure of sulfated alumina and titania and postulated that in the absence of water three oxygens of the sulfate are bonded to Al or Ti, whereas in the presence of HzO this is converted to a bridged bidentate sulfate, thus accounting for the increased Bronsted acidity (161). 

Monk-Irwin An unsuccessful predecessor of the Sulfate process for making titanium dioxide pigment from ilmenite. Invented by C.R. Whittemore at McGill University, Montreal, in the early 1920s and subsequently developed by J. Irwin and R.H. Monk in Canada and B. Laporte Limited in Luton, UK. Ilmenite from the deposit at Ivry, Quebec was reduced by heating with coke, leached with ferric chloride solution, and then roasted with a mixture of sulfuric acid and sodium sulfate. The resulting cake, containing titanyl sulfate, was dissolved in water and hydrolyzed, and the titania hydrate calcined. Some of the product was extended with barium sulfate. The project was abandoned in 1928. 

---