Titanium oxide-based catalysts

Initial experimentation aimed at demonstrating the principle feasibility of the appealingly simple adsorptive Claus process concept described in the previous section yielded promising results indicating excellent harmonization between the catalytic and adsorptive processes for a commercial titanium oxide-based catalyst and a 3A zeolite adsorbent, respectively [30], The amounts of water vapor adsorbed... 

The r-butyl alcohol, co-product produced at the rate of 15 t/t<3) of propylene oxide, depending on whether or not a market is available, is utilized as such or dehydrated to isobutene (200°C, atmospheric pressure, titanium oxide base catalyst). If the isobutene is itself unusable, it can be hydrogenated to isobutane, which is recycled. The good antiknock properties of r-butyl alcohol currently mak/ it a highly popular additive for automotive gasolines. In addition, certain recent processes (Mitsubishi Rayon, Nippon Shokubal Oxirane) can be used to convert the r-butyl alcohol to metbacrylic acid (see Section 11.2.3.2). 

S. Matsuda and K. Kato, "Titanium Oxide Based Catalysts-a Review", Appl. Catal.. 1983,8. 149-165. 

Q Photocatalysis Photocatalysis on Titanium Oxide-Based Catalysts... 

LLDPE resias are produced ia iadustry with three classes of catalysts (11—14) titanium-based catalysts (Ziegler), metallocene-based catalysts (Kaminsky and Dow), and chromium oxide-based catalysts (Phillips). 

In this chapter, advanced research work on such photofunctional catalysts and photocatalytic systems are introduced (i) Design and development of second-generation Ti02 photocatalysts that can operate under visible light irradiation. (ii) Photocatalytic performance of titanium oxide-based thin film catalysts, (iii) Photocatalytic decomposition of water into H2 and O2 using Ti02 thin film photocatalysts, (iv) Characterizations of the local structures of the active sites of Ti-MCM-41 catalysts and their photocatalytic reactivity for the decomposition of NO into N2 and O2. 

Photocatalytic Performance of Titanium Oxide-Based Thin Film Catalysts... 

Up to now selective catalytic reduction has been the completely dominant method of flue gas NOx treatment. In this method ammonia is injected in the flue gas in the presence of a catalyst, commonly titanium oxide based, to reduce NO and NO2 to nitrogen and water. The catalyst can be placed in different positions in the flue gas flow, the important factor being that conditions such as the flue gas temperature are optimal (usually 300-400 C). The positions used for catalyst are high dust, where the catalyst is placed between the economiser and the air preheater low dust, with the catalyst situated after a hot gas precipitator and before the air pre-heater and tail end, with the catalyst situated after the desulphurisation plant (see Figure 1). The most widely used position worldwide is high dust, where untreated flue gas containing sulphur dioxide and particulates passes through the catalyst. 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Numerous modifications of chromium-based catalysts have been made through the introduction of various additives, the most effective of which are titanium alkoxides (38,39). These additives apparentiy reduce surface silyl chromate moieties to chromium titanates, which are then oxidized to titanyl chromates. These catalysts offer a better control of the resin molecular weight (39). 

It is carried out in the Hquid phase at 100—130°C and catalyzed by a soluble molybdenum naphthenate catalyst, also in a series of reactors with interreactor coolers. The dehydration of a-phenylethanol to styrene takes place over an acidic catalyst at about 225°C. A commercial plant (50,51) was commissioned in Spain in 1973 by Halcon International in a joint venture with Enpetrol based on these reactions, in a process that became known as the Oxirane process, owned by Oxirane Corporation, a joint venture of ARCO and Halcon International. Oxirane Corporation merged into ARCO in 1980 and this process is now generally known as the ARCO process. It is used by ARCO at its Channelview, Texas, plant and in Japan and Korea in joint ventures with local companies. A similar process was developed by Shell (52—55) and commercialized in 1979 at its Moerdijk plant in the Netherlands. The Shell process uses a heterogeneous catalyst of titanium oxide on siHca support in the epoxidation step. Another plant by Shell is under constmction in Singapore (ca 1996). 

The process has been commercially implemented in Japan since 1977 [1] and a decade later in the U.S., Germany and Austria. The catalysts are based on a support material (titanium oxide in the anatase form), the active components (oxides of vanadium, tungsten and, in some cases, of molybdenum) and modifiers, dopants and additives to improve the performance, especially stability. The catalyst is then deposited over a structured support based on a ceramic or metallic honeycomb and plate-type structure on which a washcoat is then deposited. The honeycomb form usually is an extruded ceramic with the catalyst either incorporated throughout the stmcture (homogeneous) or coated on the substrate. In the plate geometry, the support material is generally coated with the catalyst. 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

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