Oxidation of Alcohols and Aldehydes on Metal Catalysts

Liquid-phase oxidations of alcohols in the presence of supported metal catalysts are potentially very attractive reactions for the preparation of intermediates and fine chemieals because high selectivities can be obtained with environmentally clean processes. Indeed, they proceed under mild conditions, with molecular oxygen as oxidizing agent and water as solvent. Supported catalysts, based mainly on platinum-group metals, are resistant to leaching, are recyclable, and are readily available from catalyst manufacturers in various compositions and forms. 

It was found as early as the middle of the 19th century that oxidation of alcohols to aldehydes and acids with molecular oxygen is catalyzed by platinum metals, but these reactions have been comparatively little studied. After the pioneering work of Heyns et al. [1,2] most of the reports in the open literature were published by a small number of research groups at Eindhoven [3-24], Delft [25-39], Zurich [40-56], and Villeurbanne [57-68], and the oxidation of glycerol and derivatives was studied by Kimura [69-74]. A few review papers were devoted to the liquid-phase oxidation of alcohols and carbohydrates on metal catalysts [31,48, 75-77]. 

In Section 9.2.2 the physicochemical aspects of metal-catalyzed oxidation reae-tions of alcohols and aldehydes, including carbohydrates, will be analyzed. Selected examples of oxidation reactions will be considered in section 9.2.3 excluding those of carbohydrates, which are treated separately in Section 9.3. 

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M. Besson, and P. Gallezot, Selective oxidation of alcohols and aldehydes on metal catalysts, Catal. Today 57(1-2), 127-141 (2000). 

Besson, M. and Gallezot, P. (2000). Selective Oxidation of Alcohols and Aldehydes on Metal Catalysts, Catal. Today, 57, pp. 127-141. 

Hydrocarbon oxidation is a maj or field of research. Generally, the most challenging aspect is not the oxidation itself but to achieve selectivity towards alcohols and aldehydes/ketones. Hence a large number of reports on iron-catalyzed procedures have appeared in recent years. The major drawback of the present systems is their low activity, presumably due to decomposition of H202 in the presence of transition metals (catalase activity) and oxidative degradation of the catalyst. 

Table 1 summarizes the experimental results obtained in our laboratory on the kinetics of the normal dehydrogenation of hydrocarbons (hexahydro-aromatics to aromatics, the open chain compounds butylene to butadiene, and ethylbenzene to styrene), of amines to ketimines, and of alcohols to aldehydes or to ketones, respectively, in the presence of metallic or oxide catalysts. Equation (1) was found to apply in all cases. Ko and h are given by... 

Thus, in the fine chemicals industry, reduction of ketones and aldehydes relies mainly on the use of complex metal hydrides that require time-consuming workup of reaction mixtures and produce significant amounts of inorganic and organic wastes. Similarly, the oxidation of alcohols into carbonyls is traditionally performed with stoichiometric inorganic oxidants, notably Cr(VI) reagents or a catalyst in combination with a stoichiometric oxidant [1]. 

The aim of this work was to develop and present a new method for the synthes selective platinum catalysts for the hydrogenation of unsaturated aldehydes to unsatui alcohols. The method of preparation presented above makes it possible to obtain cata possessing polar platinum surface, due to the presence of active centers near the intei metal - partially reduced transition metal oxide. This transition metal oxide adsorb carbonyl oxygen atom whereas adjacent platinum atom interacts with carbonyl ca atom. In such a situation, the C=C bond is quite far from the surface so its adsorption i favored. There are also some additional parameters which should be taken consideration. The first is the size of platinum crystallites located on the catalyst sur Large platinum crystallites cause planar adsorption of aldehyde molecule in such adsorption of both double bonds is highly probable. It is known that a more sur... 

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