Oxidative dehydrogenation of alcohols

Skeletal catalysts are usually employed in slurry-phase reactors or fixed-bed reactors. Hydrogenation of cottonseed oil, oxidative dehydrogenation of alcohols, and several other reactions are performed in sluny phase, where the catalysts are charged into the liquid and optionally stirred (often by action of the gases involved) to achieve intimate mixing. Fixed-bed designs suit methanol synthesis from syngas and catalysis of the water gas shift reaction, and are usually preferred because they obviate the need to separate product from catalyst and are simple in terms of a continuous process. 

Strength against attrition is particularly important for catalysts in slurry-bed reactors, where physical breakage of the catalyst particles, ultimately to fines, can prevent their use for those reactions. The strength of the high surface area skeletal structures can be contrasted against activated carbon, which readily breaks down due to attrition in these types of environments. For the few environments where attrition is still a problem (e.g., oxidative dehydrogenation of alcohols), the skeletal catalytic material... 

There are numerous indications in the literature on catalyst deactivation attributed to over-oxidation of the catalyst (3-5). In the oxidative dehydrogenation of alcohols the surface M° sites are active and the rate of oxygen supply from the gas phase to the catalyst surface should be adjusted to that of the surface chemical reaction to avoid "oxygen poisoning". The other important reason for deactivation is the by-products formation and their strong adsorption on active sites. This type of... 

Since these are chemical equilibriiun reactions, by modifying the reaction conditions, i.e., using acetone as solvent instead of isopropanol, the reaction can be reversed, and therefore used for the oxidation (dehydrogenation) of alcohols (Oppenauer-type oxidation) [43]. Moreover, since acetone is the hy-... 

The key step in this category involves the oxidation of a coordinated substrate by a metal ion or an oxometal species (see later). Examples include the palladium(II)-catalyzed oxidation of olefins (Wacker process) and the oxidative dehydrogenation of alcohols, where the key steps are reactions (5) and (6), respectively. 

The oxidized form of the metal ion is subsequently regenerated by reaction of the reduced form with molecular oxygen. A special case of reaction (6) is involved in the oxidative dehydrogenation of alcohols over supported metals (see later). 

Oxidative dehydrogenation of alcohols is a new approach in the development of industrial processes for the synthesis of aldehydes and ketones [103-105], In this regard, the technologically most suitable is the method of acetaldehyde synthesis in the presence of melted vanadium oxide, alkaline metals with promoting additives, alkaline metal sulfates or chlorides as catalysts [105], The target product yield equals 65.9% per used alcohol at 69.2% conversion. The disadvantage of the method is the relatively low yield of the target product... 

Modern variations include the in situ, and thus catalytic, use of this high-valent selective reagent, not only for alcohols but also for ethers (see later). Ru(VII) (perruthenate) in the compounds tetra-n-butylammonium perruthenate (TBAP) and tetra-n-propylammonium perruthenate (TPAP) has found wide application in alcohol oxidation. Ru-oxo complexes with valence states of IV to VI are key intermediates in, for example, the selective oxygen transfer to alkenes, leading to epoxides. On the other hand 16-electron Ru(II) complexes can be used to catalyse hydrogen transfer thus these are excellent catalysts for oxidative dehydrogenation of alcohols. A separate section is included to describe the different mechanisms in more detail. 

Elemental copper can be used as an unsupported catalyst for the oxidative dehydrogenation of alcohols to their respective aldehydes. There are two main reaction paths partial oxidation to formaldehyde and total oxidation to carbon dioxide, which is thermodynamically favored. The... 

It is assumed that also the oxidative dehydrogenation of alcohols like methanol, ethanol and isopropanol with the polyPc goes through hydrogen abstraction at the oxygen bond. The polymers prepared from TCB and CU2CI2 in bulk were treated at 393 K... 

Quinones are effective cocatalysts for both homogeneous and supported POM-based catalytic oxidative dehydrogenation of alcohols... 

Introduction.—The oxidative dehydrogenation of alcohols to aldehydes and ketones over various catalysts, including copper and particularly silver, is a well-established industrial process. The conversion of methanol to formaldehyde over silver catalysts is the most common process, with reaction at 750—900 K under conditions of excess methanol and at high oxygen conversion selectivities are in the region 80—95%. Isopropanol and isobutanol are also oxidized commercially in a similar manner. By-products from these reactions include carbon dioxide, carbon monoxide, hydrogen, carboxylic acids, alkenes, and alkanes. 

Newmann R, Levin M (1991) Selective aerobic oxidative dehydrogenation of alcohols and amines catalyzed by a supported molybdenum-vanadium heteiopolyanion salt. J Oig Chem 56 5707-5710... 

Finally, supported noble metals widely used as hydrogenation catalysts can be used to catalyze the reverse reaction-oxidative dehydrogenation-in the presence of oxygen. This is applied, for example, in the oxidative dehydrogenation of alcohols and carbohydrates (see Sections 9.2 and 9.3). 

The oxidative dehydrogenation of alcohols represents key steps in the synthesis of aldehyde, ketone, ester, and acid intermediates employed within the fine chemical, pharmaceutical, and agrochemical sectors, with allylic aldehydes in particular high-value components used in the perfume and fiavoring industries [1]. For example, crotonaldehyde is an important agrochemical and a valuable precursor for the food preservative sorbic acid, while citronellyl acetate and cinnamaldehyde confer rose/fruity and cinnamon flavors and aromas, respectively. There is also considerable interest in the exploitation of biomass-derived feedstocks such as glycerol (a by-product of biodiesel synthesis from plant or... 

Oxidative dehydrogenation of alcohols with 0 using metal complex... 

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