Oxidative dehydrogenation definition

As an example, the joint analysis of IR and Raman spectra provided evidence of the partial ordering of cations in a Fe-Cr corundum-type mixed sesquioxides, which are used industrially as high temperature water-gas shift catalysts, but are also active in olefin oxidative dehydrogenation. X-ray diffraction (XRD) patterns of these solids indicate the conmdum-type structure without any superstructure. This implies that iron and chromium ions are randomly distributed. IR and Raman spectra instead definitely show that cations are at least partially ordered in layers such as in the ilmenite-type superstructure. Similarly, XRD analysis shows a cubic (non-ferroelectric) structure of nanometric BaTi03, while vibrational spectroscopies reveal microscopic asymmetry of this structure. Similarly, IR spectroscopy allowed the determination of the state of vanadium in solid solution in Ti02 anatase catalysts, and the presence of Ti" + in the silicalite framework of TSl catalysts, " used for the selective oxidation of phenol and the ammoximation of cyclohexanone with hydrogen peroxide. 

Despite the apparent attractiveness of the conversion of natural gas into high value chemicals as a cheap raw material, the nature of the alkanes (i.e., inertness in chemical reaction at mild temperatures) is a definite obstacle. The way to overcome this problem is by finding a cafalysf, which is able fo acfivafe fhe alkane under mild conditions and selectively transform it into a desired product. Many different reactions have been studied and within them, particularly, dehydrogenation, oxidative dehydrogenation (ODH), and partial oxidation. 

Villa et al. [340] have shown that the bismuth tungstates are comparable with bismuth molybdates with respect to dehydrogenation catalysis, although activities and selectivities are somewhat lower. Although the phase structures are different, interesting catalysts are formed in a similar composition range Bi/W = 2/3 to 2/1. (Note that, in case of propene (amm)oxidation, tungstates are definitely inferior to molybdates.)... 

Hofmann degradation of the crystalline mesembrine methiodide afforded a definite desmethylmesembrine but further degradation failed (11). Alkali fusion, degradation by ozone, and selenium dehydrogenation (6) were also without success. Oxidation with potassium permanganate produced 3,4-dimethoxyphenylglyoxylic acid and 3,4-dimethoxy-benzoic acid (7). 

On our catalysts, the oxy-dehydrogenation of butenes to butadiene via the above elimination way is definitely faster than the evolution via the dehydrogenation way. The methyl-vinyl ketone, formed from but-3-en-2-oxides is further easily oxidized because of its ability to give enolization [20], and finally gives rise to total combustion to carbon oxides. Carboxylate species are likely intermediates in this way. 

Although ethanol is dehydrogenated to acetaldehyde in the presence of zinc oxide at temperatures of 300° to 400° C. and atmospheric pressure, no aldehyde results when the reaction is conducted under sufficient hydrogen pressure. Instead a complex mixture including esters of acetic, butyric, and caproic acids and alcohols up to and higher than octyl is formed.01 Condensation reactions of acetaldehyde are used to account for the formation of these compounds but no definite proof has as yet been advanced to establish the mechanisms. 

In particular, LADHs catalyze the reversible dehydrogenation of primary and secondary alcohols to aldehydes and ketones, respectively. Other enzymatic activities of LADHs are aldehyde dismutation and aldehyde oxidation. The physiological role, although surely related to the metabolism of the above species, is not definitely settled. Much effort is being devoted to understanding the mechanism of action of this class of enzymes, which have obvious implications for the social problem of alcoholism. 

No proof has been obtained that a 3//-indolylidene (or the corresponding cation) is an intermediate in the oxidative cyclization, and it must be concluded that the substrate remains bound to the same site on the enzyme molecule throughout the whole process. It can be expected that a (reactive) compound similar in structure to the proposed intermediate will not be released from the enzyme after the dehydrogenation reaction. Further elucidation of the mechanism of the conversion of pCA into aCA requires more definite evidence that the cyclization step is also catalyzed by the enzyme. Efforts to obtain such evidence are complicated by the fact that the isoenzymes do not catalyze the reverse reaction namely, the conversion of aCA into pCA (Schabort and Potgieter, 1971). 

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