Titania source

Scattered results are reported in [2979], and there are too few data points near the IEP. Also, in [2980,2981], too few data points are available near the IEP to make a reliable estimate. In [2982], at one pH value is reported. In [2983], potentials were measured only at pH 1,4, and 12. The IEP was obtained in [2984] from ESA measurements for two titanias (source or characterization of the powers or experimental details were not reported). The unusually high IEP reported in [2984] may be due to experimental errors the sohd concentration was too low, and the electrolyte background was not subtracted. Among the results from [1726], only the IEP for Nd(Ol I), was used. The other lEPs are based on arbitrary interpolations. The pH reported in the (pH) plot in [208] was not the pH of the dispersion. A home-made apparatus was used in [267], atypical shapes of electrokinetic curves... 

Calcination, 823 K, 2h (support)+2h(precipitated sample) alcohol/AI (mol/mol) = 4, Ti/Al=l. a) Titanium alkoxide which was prepared from titanium iso-propoxide and 1-phenylethanol by ligand exchange reaction was used as a titania source. 

Silica-titania photocatalysts were prepared from Si(OEt)4 (TEOS) and Ti(OBu)4 as silica and titania sources by the following sol-gel method, as summarized in scheme 1. A clear mixture of TEOS, EtOH, H2O, and HCl (mol ratio = 1 4 1 0.6) was stirred at room temperature for x min. A yellow and clear mixture of Ti(OBu)4, EtOH, and (CH3C0)2CH2 (mol ratio = 0.01 1 0.005) was added and stirred for y min at room temperature. The clear mixed solution was stirred and dried at 353 K typically for 1 h until clear gel was obtained. The wet gel was dried at 383 K ovemi t, then calcined in air... 

TS-1 can be synthesised by hydrothermal methods using a variety of silica and titania sources, structure-directing agents and mineralisers. Alkali metal hydroxides cannot be used in the syntheses, however, because their presence results in the precipitation of separate titanate phases. It is only possible to... 

Padovan et al. [38, 39] developed a method based on the impregnation of dried microspherical porous silica up to incipient wetness with an aqueous solution obtained by hydrolyzing the titania source (tetraisopropylorthotitanate) with TPAOH, followed by calcination at 448 K in a sealed glass tube. Pure and well crystallized TS-1 is obtained after 10 hours, while extra-framework titanium species start to appear after longer crystallization times. 

The large pore Ti-ZSM-12 (or TS-12) has been recently prepared by Tuel by adopting a procedure based on the mixed alkoxide method [84]. TEOS and TBOT were used as sihca and titania sources, respectively, while the template agent was hexamethylene bis(diethyhnethylammoniiun hydroxide). The incorporation of Ti was hmited to 0.45 Ti per unit cell (x=0.016) [84]. 

In the case of titanium, this route has been attempted for the framework types listed in Table 5, using aqueous solution of (NH4)2TiFg [88] or TiCl4 vapor [89-91] as titania source. When the microporous precursor is contacted with aqueous (NH4)2TiFg at 75 - 95°C, a partial dealumination of the framework occurs accompanied by deposition of a large amount of titanium. However, no clear evidence supporting true incorporation of Ti is given [54,88]. 

Minerals. Iron-bearing minerals are numerous and are present in most soils and rocks. However only a few minerals are important sources of iron and thus called ores. Table 2 shows the principle iron-bearing minerals. Hematite is the most plentiful iron mineral mined, followed by magnetite, goethite, siderite, ilmenite, and pyrite. Siderite is unimportant in the United States, but is an important source of iron in Europe. Tlmenite is normally mined for titania with iron as a by-product. Pyrite is roasted to recover sulfur in the form of sulfur dioxide, leaving iron oxide as a by-product. 

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

In the area of pollution control, file removal of NOx from stationary sources effluents, such as power plant stack gases, has been accomplished by use of titania-vanadia catal)rsts, which promote the reduction of NOx with NH3 to produce nitrogen and water. 

The graduation of material across a wafer was achieved using a wedge shutter controlling the deposition profile of each source independently the principle is discussed in detail elsewhere [Guerin and Hayden, 2006]. For uniform depositions such as carbon and titania support materials, the sample holder was equipped with a motor drive that allowed rotation of the substrate during deposition. 

In Figure 34.7b, the relative selectivity to byproducts such as EG and organic acids is shown (primarily acetic, lactic and glyceric acids). Not all carbon supports are equivalent, as there are a wide variety of source materials that are used in their production. Note that the highest acid selectivity is shown with the catalyst based on a graphitic carbon and on a carbon support first treated with titania. 

We may thus conclude after this short overview on DeNO technologies that NH3-SCR using catalysts based on V-W-oxides supported on titania is a well-established technique for stationary sources of power plants and incinerators, while for other relevant sources of NO, such as nitric acid tail gases, where emissions are characterized from a lower temperature and the presence of large amounts of NOz, alternative catalysts based on transition metal containing microporous materials are possible. Also, for the combined DeNO -deSO, alternative catalysts would be necessary, because they should operate in the presence of large amounts of SO,.. Similarly, there is a need to develop new/improved catalysts for the elimination of NO in FCC emissions, again due to the different characteristics of the feed with respect to emissions from power plants. 

Presently the catalytic selective NOx reduction by ammonia is efficient and widespread through the world for stationary sources. The remarkable beneficial effect of 02 for the complete reduction of NO into nitrogen is usually observed between 200 and 400°C. However, such a technology is not applicable for mobile sources due to the toxicity of ammonia and vanadium, which composes the active phase in vanadia-titania-based catalysts. Main drawbacks related to storing and handling of ammonia as well as changes in the load composition with subsequent ammonia slip considerably affect the reliability of such a process. On the other hand, the use of urea for heavy-duty vehicles is of interest with the in situ formation of ammonia. 

Photoinduced deposition of various noble metals onto semiconductor particles has been extensively reported [310-315]. Several factors are controlling this reaction. To control the morphology of metal clusters with desired size and distribution pattern on a given surface area of titania, the most relevant factors are the surfactant, pH, local concentration of cations, and the source of cation [316], In the case of the Ag clusters, the reaction steps proposed include the creation of electron (e )-hole (p+) pairs, the reaction of holes with OH surface species, and the reaction of electrons with adsorbed Ag+ ions ... 

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. 

In research laboratories, different types of light sources are used instead of solar radiation. In most cases the simulated spectrums have considerable deviation from the solar spectrum. Based on equation (3.6.9) Murphy et al [109] analyzed the maximum possible efficiencies for different materials according to their band gap in the case of solar global AM 1.5 illumination and xenon arc lamp, see Fig. 3.21. For example, anatase titania with a bandgap of 3.2 eV has a maximum possible efficiency of 1.3% under AM 1.5 illumination, and 1.7% using Xe lamp without any filter. For rutile titania these values are 2.2% and 2.3% respectively. 

Fig. 7 FESEM images of titania nanocoil produced by anodic oxidation (a). The cartoon shows schematically the photocurrent generated by light irradiation of nanocoil containing a catalyst particle (b) and the associated magnetic field (c). Source Centi and Perathoner. ...

Owing to the limited domestic supply of rutile (a mixed titania and zirconia containing ore) much effort is being directed toward commercial development of rutile made from il-menite, an abundant Ti ore. A factor for a long term pressure on the price ofZris the probability of utilization of rock deposits of ilmenite as the principle source of Ti. Rock-type deposits do not contain Zr in recoverable quantities... 

High conversion levels of TCE were achieved in a bench scale flat plate fluidised bed photoreactor with a silica supported titania catalyst [204], A supported catalyst was used as the titania fluidisation characteristics were considered to be poor. It was found that the stoichiometric reaction 34 required the simultaneous presence of oxygen, water vapour and TCE. In order to maximise the titania threshold of 350 to 400 nm a single 4-W fluorescent UV source was used. At low concentrations of TCE the oxidation rate was independent of the water concentration whereas the rate of oxidation of the TCE was inhibited by water vapour when the concentrations of the pollutant had increased. Without any water vapour the photooxidation activity of the catalyst rapidly declines. In the presence of water, however, at high TCE concentrations there was a marked deactivation with the photocatalyst. 

One of the first fluidized bed photocatalytic reactors was presented by Dibble and Raupp (1992), who used silica-supported titania catalysts in order to degrade TCE with an AQE of 13%. Here, the UV sources in this bench-scale reactor were located externally to the reactor. Catalyst loss was prevented in this laboratory-scale reactor by introducing a second glass frit located at the reactor outlet. 

---