Catalysis chromium oxide

The metal oxide catalyzed polymerization of ethylene takes place under conditions of medium pressure and temperature. It is practiced according to two methods, the Phillips process and the Standard Oil process (also known as the Indiana process) the former is based on chromium oxide catalysis, whereas the latter uses molybdenum oxide. The Phillips process dominates the field of metal oxide catalysis. Chromium oxide catalysis is the most widely used method for the production of high density polyethylene, accounting for a little more than half the worldwide output. 

The action nl catalysis cun he illustrated hy an cxample-the water gas shift reaction catalyzed by iron and chromium oxides. 

Oxidation of (S)-(-)-2-methyl-1-butanol to (S)-(+)-2-methylbutanal has been previously carried out in low yields by chromium oxidation,9 under phase transfer catalysis,10 or by Swern oxidation in the presence of tributylamine.11... 

Alcohols may be oxidized in a similar way. However, these reactions strongly resemble those reported for Cr molecular sieves, and a small concentration of Cr in solution may well account for most of the observations of catalysis. Binary molybdenum-chromium oxides supported on alumina have been used in the autoxidation of cyclohexene with 02 and r-BuOOH as an initiator (62). This is a complex reaction in which uncatalyzed and Cr-catalyzed oxidation combine to yield 2-cyclohexen-l-one, 2-cyclohexen-l-ol, and 2-cyclohexenyl hydroperoxide the Mo compound can use the hydroperoxide formed in situ as an oxidant for the epoxidation of cyclohexene. Although much lower oxygen consumption was observed for the reaction filtrate than for the suspension, it is unclear how the Cr is held by the oxide. 

Weckhuysen, B.M., Verberckmoes, A.A., Debaere, J., Ooms, K., Langhans, 1. and Schoonheydt, R.A. (2000) In situ UV-Vis diffuse reflectance spectroscopy-on line activity measurements of supported chromium oxide catalysts relating isobutane dehydrogenation activity with Cr-spedation via experimental design. Journal of Molecular Catalysis A Chemical, 151 (1-2), 115-31. 

Hutchings, G.J., Copperthwaite, R.G., Gottschalk, F.M., Hunter, R., Mellor, J., Orchard, S.W., and Sangiorgio, T. A comparative evaluation of cobalt chromium oxide, cobalt manganese oxide, and copper manganese oxide as catalysts for the water-gas shift reaction. Journal of Catalysis, 1992, 137, 408. 

Aluminum phosphates are the most commonly used phosphates for polymerization catalyst supports because they can be made with the high porosity that is necessary for fragmentation. However, many other metal phosphates are also known and are used in other areas of catalysis. These materials are often quite acidic and can also serve as supports for chromium oxide. 

J. Sloczynski, B. Grzybowska, R. Grabowski, A. Kozlowska and K. Wcislo, Oxygen adsorption and catalytic performance in oxidative dehydrogenation of isobutane on chromium oxide-based catalysts, Phys. Chem. Chem. Phys., 1(2), 333-339, 1999. A. Bielanski and J. Haber, Oxygen in catalysis, Dekker New York, 1991. 

Ji, M., Hong, D., Chang, J., et al. (2004). Oxidative dehydrogenation of ethane with carbon dioxide over supported chromium oxide catalysts, in S. Park, J. Chang and K. Lee (eds). Carbon Dioxide Utilisation for Global Sustainability (Studies in Surface Science and Catalysis, 153), Elsevier, Amsterdam, pp. 339-342. 

Chromium compounds decompose primary and secondary hydroperoxides to the corresponding carbonyl compounds, both homogeneously and heterogeneously (187—191). The mechanism of chromium catalyst interaction with hydroperoxides may involve generation of hexavalent chromium in the form of an alkyl chromate, which decomposes heterolyticaHy to give ketone (192). The oxidation of alcohol intermediates may also proceed through chromate ester intermediates (193). Therefore, chromium catalysis tends to increase the ketone alcohol ratio in the product (194,195). 

The oxidation of tartaric and glycollic acid by chromic acid also induces the oxidation of manganous ions. In the presence of higher concentrations of manganese(II) the rate of oxidation of the acids is diminished to about one-third of that in the absence of manganous ions. The decrease of the rate has been attributed to manganese(II) catalysis of the disproportionation of the intermediate valence states of chromium probably chromium(IV). 

Shiny silvery metal that is relatively soft in its pure form. Forms a highly resistant oxide coat. Used mainly in alloys, for example, in construction steel. Tiny amounts, in combination with other elements such as chromium, makes steel rustproof and improves its mechanical properties. Highly suited for tools and all types of machine parts. Also applied in airplane turbines. Chemically speaking, the element is of interest for catalysis (for example, removal of nitric oxides from waste gases). Vanadium forms countless beautiful, colored compounds (see Name). Essential for some organisms. Thus, natural oil, which was formed from marine life forms, contains substantial unwanted traces of vanadium that need to be removed. 

The question about the competition between the homolytic and heterolytic catalytic decompositions of ROOH is strongly associated with the products of this decomposition. This can be exemplified by cyclohexyl hydroperoxide, whose decomposition affords cyclo-hexanol and cyclohexanone [5,6]. When decomposition is catalyzed by cobalt salts, cyclohex-anol prevails among the products ([alcohol] [ketone] > 1) because only homolysis of ROOH occurs under the action of the cobalt ions to form RO and R02 the first of them are mainly transformed into alcohol (in the reactions with RH and Co2+), and the second radicals are transformed into alcohol and ketone (ratio 1 1) due to the disproportionation (see Chapter 2). Heterolytic decomposition predominates in catalysis by chromium stearate (see above), and ketone prevails among the decomposition products (ratio [ketone] [alcohol] = 6 in the catalytic oxidation of cyclohexane at 393 K [81]). These ions, which can exist in more than two different oxidation states (chromium, vanadium, molybdenum), are prone to the heterolytic decomposition of ROOH, and this seems to be mutually related. 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

We believe that catalysis occurs by formation of a complex between acetaldehyde, peracetic acid, and the metal ion in the 3+ oxidation state. The metal ion could be acting as a superacid as for peracetic acid decomposition, although oxidation-reduction reactions within the complex cannot be ruled out. Here again, we have found a disturbing lack of catalytic activity of other trivalent metals (aluminum, iron, and chromium). Simple acid catalysis is not as effective as proved when using p-toluenesulfonic acid and acetyl borate. This indicates that at least more than one coordination position is needed to obtain a complex of the proper configuration. 

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