Alkenes oxidation solid catalysts

Solid catalysts for the metathesis reaction are mainly transition metal oxides, carbonyls, or sulfides deposited on high surface area supports (oxides and phosphates). After activation, a wide variety of solid catalysts is effective, for the metathesis of alkenes. Table I (1, 34 38) gives a survey of the more efficient catalysts which have been reported to convert propene into ethene and linear butenes. The most active ones contain rhenium, molybdenum, or tungsten. An outstanding catalyst is rhenium oxide on alumina, which is active under very mild conditions, viz. room temperature and atmospheric pressure, yielding exclusively the primary metathesis products. 

Hydration means, in general, addition of the elements of water to a substance. Most of these reactions are non-catalytic or homogeneously catalysed processes. In this section, only hydration of olefins to alcohols, of acetylene to acetaldehyde, and of alkene oxides to glycols will be treated, since they are typical reactions where the application of solid catalysts has become important. 

Most alcohols also will dehydrate at fairly high temperatures in the presence of solid catalysts such as silica gel or aluminum oxide to give alkenes or ethers. The behavior of ethanol is reasonably typical of primary alcohols and is summarized in the following equations ... 

Other examples of Michael additions are the reaction of nitroolefins with acetone on L-proline-modified Mg-Al mixed oxides (51) or with diethyl malonate on metalorganic MCM-41 (52), or the addition of nitromethane to unsaturated carbonyl compounds on KF-modified alumina (53). Furthermore, solid catalysts such as montmorillonite clays and hydroxyapatite have recently been employed for the construction of S—C bonds by /lia-Michael addition of thiols to unsaturated ketones and other carbonyl compounds (54,55). Similarly, aza-Michael additions of amines to alkenes activated by -CN, -COOR, or -COR groups, lead to C—N bond containing products on Amberlyst-15 or polyaniline supported Cul (56,57). 

The pros and cons of oxidative dehydrogenation for alkene synthesis using doped cerianites as solid oxygen carriers are studied. The hydrogen oxidation properties of a set of ten doped cerianite catalysts (Ce0.9X0.1Oy, where X = Bi, In, La, Mo, Pb, Sn, V, W, Y, and Zr) are examined under cyclic redox conditions. X-ray diffraction, X-ray photoelectron spectroscopy, adsorption measurements, and temperature programmed reduction are used to try and clarify structure-activity relationships and the different dopant effects. 

The direct conversion of propene to its epoxide, in near quantitative yields, with aqueous H202 will be environmentally more benign. One of the unique features of TS-1 as a solid oxidation catalyst is its ability to utilize aqueous H202 as the oxidant for such conversions. This ability of TS-1 derives from the fact that silicalite-1 is hydrophobic, in contrast to the hydrophilic amorphous Ti-Si02. Consequently, hydrophobic reactants, such as alkenes, are preferentially adsorbed by TS-1, thus precluding the strong inhibition by H20 observed with amorphous Ti-Si02. 

Co-containing POMs have been found to be among the most efficient catalysts for homogeneous aerobic oxidation and co-oxidation processes [91-93]. This prompted many researchers to design solid Co-POM-containing materials [78,94-100]. Thus, various Co-POMs have been deposited on cotton cloth [94] and silica [100], datively [95] or electrostatically [96,97] bonded to NH2-modified silica surfaces (vide infra) as well as intercalated in LDHs [78,98,99]. The resulting materials were successfully used for aerobic oxidation of aldehydes, alkenes, alkanes, alcohols and some other organic substrates. 

Different catalysts bring about different types of isomerization of hydrocarbons. Acids are the best known and most important catalysts bringing about isomerization through a carbocationic process. Brpnsted and Lewis acids, acidic solids, and superacids are used in different applications. Base-catalyzed isomerizations of hydrocarbons are less frequent, with mainly alkenes undergoing such transformations. Acetylenes and allenes are also interconverted in base-catalyzed reactions. Metals with dehydrogenating-hydrogenating activity usually supported on oxides are also used to bring about isomerizations. Zeolites with shape-selective characteristics... 

Attempts have recently been made to prepare solid acids by loading triflic acid into various inert oxides including silica,184 titania,185,186 and zirconia.187,188 Silica functionalized with anchored aminopropyl groups was also used to immobilize triflic acid.189 These new catalysts have been tested in a variety of organic transformations, such as alkane-alkene alkylation, Friedel-Crafts acylation, alkene dimerization, and acetalization. Silica nanoboxes prepared by dealumination of Na-X- and Ca-A-type zeolites were also loaded with triflic acid up to 32 wt%.190 The materials were thoroughly characterized but have not been tested as catalysts. 

---