Titanium heterogeneous catalysis

Heterogeneous Catalysis. The main discovery of the 1980s was the use of titanium sihcaUte (TS-1) a synthetic zeoHte from the ZSM family containing no aluminum and where some titanium atoms replace siUcon atoms in the crystalline system (Ti/Si = 5%) (33). This zeoHte can be obtained by the hydrolysis of a siUcate and an alkyl titanate in the presence of quaternary ammonium hydroxide followed by heating to 170°C. Mainly studies have been devoted to the stmcture of TS-1 and its behavior toward H2O2 (34). The oxidation properties of the couple H2O2/TS-I have been extensively developed in... 

Several aluminum- and titanium-based compounds have been supported on silica and alumina [53]. Although silica and alumina themselves catalyze cycloaddition reactions, their catalytic activity is greatly increased when they complex a Lewis acid. Some of these catalysts are among the most active described to date for heterogeneous catalysis of the Diels-Alder reactions of carbonyl-containing dienophiles. The Si02-Et2AlCl catalyst is the most efficient and can be... 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

Pruden, A.L. and Ollis, D.F. Degradation of chloroform by photoassisted heterogeneous catalysis in dilute aqueous suspensions of titanium dioxide. Environ. Sci. Technol., 17(10) 628-631, 1983. 

Catalytic use of these compounds revealed an activity comparable to the titanium species. The most important points of this work are that under the experimental conditions there is no metal loss in solution (a rare cases in heterogeneous catalysis with such reactive media) and that the reaction is completely heterogeneous (Figure 3.29). 

In the field of heterogeneous catalysis using H2O2 as oxygen source, examples of the use of titanium-silicalite (TS-1) or Ti-beta in the oxidation of selected alcohols, with formation of a Ti-peroxo species, have been reported... 

Keywords electron transfer, heterogeneous catalysis, photochemistry, photoelectrochemistry, Titanium dioxide... 

In this paper, we will review the chemical behaviour of transition metal oxides which is of crucial importance for heterogeneous catalysis, adhesion and many technological applications. Among them, MgO(lOO) is the simplest surface, with a square unit-cell containing two ions with opposite charges titanium oxides represent another important class of systems used for their catalytic properties either directly as catalyst or indirectly as support for other catalysts (metals such as Ni, Rh for the Fischer-Tropsch reaction or V2O5 for the reduction of NOx) or as promotors[l]. The most stable surface for rutile is the (110) face. 

Heterogeneous catalysis The best known catalyst is titanium silicate - (TS-1) a synthetic zeolite of ZSM family which does not contain any aluminium and in which titanium atoms replace some silicium atoms within the crystal lattice (Ti/Si 5 %) (ref. 3). A process based on this catalysis is used in Italy (ref. 4). Although its performance levels are good, and the HQ/PC ratio can be modified (ref. 5) the high cost of the catalyst and its uncertain lifetime are the major handicaps preventing its extension. 

Another good example of greener chemistry through the use of heterogeneous catalysis is the use of TSl, a titanium siHcate catalyst for selective oxidation reactions [21] such as the 4-hydroxylation of phenol to the commercially important hydroquinone (Scheme 1.1-2). 

It is assumed that the polymerization proceeds by an anionic coordinated mechanism. That the polymerization proceeds by heterogeneous catalysis has been shown by the fact that neither the mother liquor nor precipitate affects reaction, but in combination they do (Saltman and Link, 1964 Moyer and Lehr, 1965). Whether growth occurs at a carbon-aluminum or carbon-titanium... 

Figure 10.1 (a) SS falling-film microreactor for gas-liquid reactions [14], (b) catalyst-coated SS microchannel plates [14] and (c) catalyst-coated titanium microchannel plates, stacked together for gas-phase reactions in heterogeneous catalysis [17]. 

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