Dehydrogenation oxidative

Oxidative Dehydrogenation. Specific reviews deal with oxidative dehydro-genation of lower alkanes, particularly over vanadium oxide-based cata- 

Vanadium pentoxide usually as mixed oxide was mainly investigated in the dehydrogenation of propane to yield propylene.339,345-351 The support, in most cases, is zirconia.345-349 For the dehydrogenation of butane V205-Mg0 mixed oxides were used.352,353 

Analysis of structure-activity relationships shows that various species characterized by different reactivities exist on the surface of vanadium oxide-based catalysts.339 The redox cycle between V5+ and V4+ is generally accepted to play a key role in the reaction mechanism, although opposite relationships between activity and selectivity, and reducibility were established. More recent studies with zirconia-supported vanadium oxide catalysts showed that vanadium is present in the form of isolated vanadyl species or oligomeric vanadates depending on the loading.345,346 The maximum catalytic activity was observed for catalysts with vanadia content of 3-5 mol% for which highly dispersed polyvanadate species are dominant. 

Various Mo-containing catalysts were also tested in the dehydrogenation of propane354-358 and butane.359,360 Alkali promotion was shown to have a beneficial effect, specifically to increase selectivity due to lowering the acidity of the samples.355,360 With silica-supported binary and ternary molybdates, the best results were achieved with NiMo04 and Coo.5Ni0.5Mo04 (16% yield at 27% conversion).354 

Another well-studied catalyst system is Cr203 loaded onto various supports used in almost exclusively in the oxidative dehydrogenation of isobutane to isobutylene.361-364 In the case of Cr203 on La2(C03)3, the surface active center was found to be a chromate species bound to the surface La carbonate.361 With optimum loadings between 10-15% selectivities exceed 95% below 250°C. Correlations between 

The oxidative dehydrogenation of ethylbenzene (ODE) is an alternative route to styrene, which is currently produced by dehydrogenation (DE)  

The main advantage of the ODE process is that the reaction is complete (therefore, conversions are not limited by equilibrium) and can be carried out at lower temperatures however, selective catalysts are required to minimize the formation of unwanted carbon oxides [44]. Among others, acid catalysts (such as alumina, zeolites, and metal phosphates) were tested successfully in ODE. One of the peculiar features observed with such systems was the formation of a coke layer, which was found to be the real catalytic surface [45-50]. These results suggested that carbon materials could be used as catalysts for the reaction. 

Iwasawa et al. [51] showed that polynaftoquinone, a carbonated material, was active in the ODE at low temperatures. Good results were also obtained with PPAN [52]. AUchazov et al. [53] were the first authors to test activated carbon. They observed that the ODE reaction could be performed at temperatures lower (623 to 673 K) than those normally used with oxide catalysts (723 to 823 K). Several reports on the use of activated carbon as catalyst for ODE appeared subsequently, but the results were interpreted mainly in terms of the textural properties of the catalysts (surface area/pore sizes). 

The use of carbon molecular sieves (CMSs) as catalysts for the oxidative dehydrogenation of alkyl aromatics was described in a patent by Lee [54]. Higher conversions and selectivities were reported with molecular sieve carbons with pore sizes in the range 0.5 to 0.7 nm (Carbosieve G from Supelco, and MSC-V from Calgon) than with activated carbon. This work may have triggered subsequent interest for CMS in ODE. 

In a subsequent paper [56], various carbon materials, differing in their texture, were studied. Most of the materials tested were found to be more active than 

The addition of oxygen to the butene and steam reaction mixture improves conversion and selectivity during the dehydrogenation reaction by removing the 

Not only does this improve the eqitihbriitm conversion but the exothermic oxidation reaction also supplies heat to balance the endothermic dehydrogenation reaction. At 550°-600°C more than 90% selectivity is possible at conversions in the range 65-80% with steam mole ratios rrp to 12. Catalysts in the Petrotex (Mobay) process are zinc/chromiitm and magnesirrm/chromirrm ferrites.  

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Dehydrogenation of Propionates. Oxidative dehydrogenation of propionates to acrylates employing vapor-phase reactions at high temperatures (400—700°C) and short contact times is possible. Although selective catalysts for the oxidative dehydrogenation of isobutyric acid to methacrylic acid have been developed in recent years (see Methacrylic ACID AND DERIVATIVES) and a route to methacrylic acid from propylene to isobutyric acid is under pilot-plant development in Europe, this route to acrylates is not presentiy of commercial interest because of the combination of low selectivity, high raw material costs, and purification difficulties. 

Methanol undergoes reactions that are typical of alcohols as a chemical class (3). Dehydrogenation and oxidative dehydrogenation to formaldehyde over silver or molybdenum oxide catalysts are of particular industrial importance. 

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

Production of styrene from butadiene has also been extensively investigated. Recentiy, Dow announced licensing a process involving cyclodimerization of 1,3-butadiene to 4-vinylcyclohexene, followed by oxidative dehydrogenation of the vinylcyclohexene to styrene (65,66). The cyclodimerization step takes place in... 

Most terpene-based citral (5) produced is based on the catalytic oxidative dehydrogenation of nerol (47) and geraniol (48), or by the Oppenauer oxidation of nerol and geraniol (123—125). 

Oxydehydrogenation of /i-Butenes. Normal butenes can be oxidatively dehydrogenated to butadiene in the presence of high concentration of steam with fairly high selectivity (234). The conversion is no longer limited by thermodynamics because of the oxidation of hydrogen to water. Reaction temperature is below about 600°C to minimise over oxidation. Pressure is about 34—103 kPa (5—15 psi). 

Bischler-Napieralski reaction of 139 to a 3,4-dihydroisoquinoline, oxidation, dehydrogenation and reduction of the nitro to the amino function gave 140 which was subjected to a Pschorr reaction (Scheme 49). Quaternization was accomplished by methyl iodide to furnish the isoquinolininium salt 141 which underwent an ether cleavage on heating a solid sample or benzene or DMF solution to Corunnine (127) (73TL3617). 

Acetone (2-propanone), is produced from isopropanol by a dehydrogenation, oxidation, or a combined oxidation dehydrogenation route. 

The reaction scheme is rather complex also in the case of the oxidation of o-xylene (41a, 87a), of the oxidative dehydrogenation of n-butenes over bismuth-molybdenum catalyst (87b), or of ethylbenzene on aluminum oxide catalysts (87c), in the hydrogenolysis of glucose (87d) over Ni-kieselguhr or of n-butane on a nickel on silica catalyst (87e), and in the hydrogenation of succinimide in isopropyl alcohol on Ni-Al2Oa catalyst (87f) or of acetophenone on Rh-Al203 catalyst (87g). Decomposition of n-and sec-butyl acetates on synthetic zeolites accompanied by the isomerization of the formed butenes has also been the subject of a kinetic study (87h). 

Oxidative dehydrogenation processes Catalyst development Pt group Cu, Sn, and Cl 86... 

J.N. Michaels, and C.G. Vayenas, Kinetics of Vapor-Phase Electrochemical Oxidative Dehydrogenation of Ethylbenzene,/. Catal. 85, 477-488 (1984). 

Another, and simpler, manifestation of rule Gl coming from the classical promotion literature is shown in Fig. 6.13. The rate of the oxidative dehydrogenation of C3H8 to C3H6 is first order in propane and near zero order in 02.84 As expected from rule Gl the reaction exhibits electrophobic behaviour. 

K. Chen, S. Xie, A.T. Bell, and E. Iglesia, Alkali effects of molybdenum oxide catalysts for the oxidative dehydrogenation of propane, J. Catal. 195, 244-252 (2000). 

Aldoximes can be oxidatively dehydrogenated to nitrile oxides using a variety of oxidants such as lead tetraacetate [16a], alkali hypohalites [lla],NBS in DMF followed by base treatment [16b], chloramine-T [11b], 1-chlorobenzotriazole [16c], mercuric acetate [ 16 d], etc. However, we employed either NaOCl or chloramine-T for most of our INOC reactions. For instance, a piperidine ring fused to an isoxazoline as in 14 was constructed using the INOC methodology (Scheme 3) [17]. Monoalkylation of N-tosylallylamine 10 with the bromoacetal... 

However, the pattern is complicated by several factors. The sugar molecules to be hydrogenated mutarotate in aqueous solutions thus coexisting as acyclic aldehydes and ketoses and as cyclic pyranoses and furanoses and reaction kinetics are complicated and involve side reactions, such as isomerization, hydrolysis, and oxidative dehydrogenation reactions. Moreover, catalysts deactivate and external and internal mass transfer limitations interfere with the kinetics, particularly under industrial circumstances. 

Oxidative dehydrogenation of propane over carbon nanofibers... 

As a new kind of carbon materials, carbon nanofilaments (tubes and fibers) have been studied in different fields [1]. But, until now far less work has been devoted to the catalytic application of carbon nanofilaments [2] and most researches in this field are focused on using them as catalyst supports. When most of the problems related to the synthesis of large amount of these nanostructures are solved or almost solved, a large field of research is expected to open to these materials [3]. In this paper, CNF is tested as a catalyst for oxidative dehydrogenation of propane (ODP), which is an attractive method to improve propene productivity [4]. The role of surface oxygen annplexes in catalyzing ODP is also addressed. 

Beside their use in equilibrium-restricted reactions, CMRs have been also proposed for very different applications [6], like selective oxidation and oxidative dehydrogenation of hydrocarbons they may also act as active contactor in gas or gas-liquid reactions. 

Catalytic testings have been performed using the same rig and a conventional fixed-bed placed in the inner volume of the tubular membrane. The catalyst for isobutane dehydrogenation [9] was a Pt-based solid and sweep gas was used as indicated in Fig. 2. For propane oxidative dehydrogenation a V-Mg-0 mixed oxide [10] was used and the membrane separates oxygen and propane (the hydrocarbon being introduced in the inner part of the reactor). 

Most of the results have been already partly presented in [9] (isobutane dehydrogenation) and [10] (propane oxidative dehydrogenation). Let us recall that the membrane presented in this paper has been associated with a fixed bed catalyst placed within the tube. 

In the propane oxidative dehydrogenation, where the membrane separates the two reactants, a 20% increase in the yield was observed with respect to a conventional reactor working at isoconversion [10]... 

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