Oxidative dehydrogenation of alkanes

These results suggested that 0 may be an important intermediate in the oxidative dehydrogenation of alkanes. 

Metal-oxygen bond, 27 195, 196 insertion reactions, 28 136-141 strength and selectivity, oxidative dehydrogenation of alkanes, 40 26-28... 

In spite of significant fundamental studies and its significant economic potential as an alternate route to alkenes, the oxidative dehydrogenation of alkanes to alkenes is not currently practiced.383 The main reason is that the secondary oxidation of the primary alkene products limits severely alkene yields, which becomes more significant with increasing conversion. This is due mainly to the higher energies of the C—H bonds in the reactant alkanes compared to those of the product alkenes. This leads to the rapid combustion of alkenes, that is, the formation of carbon oxides, at the temperatures required for C—H bond activation in alkanes. 

VII. Generalized Reaction Scheme for Oxidative Dehydrogenation of Alkanes... 

Short-contact-time reactions, defined as reactions occurring on a timescale of milliseconds, offer potential for conversion of hydrocarbons in one step into valuable products. Examples are the selective oxidation of methane in s)mgas without the formation of b)q5roducts (CO2, H2O, and coke) and the oxidative dehydrogenation of alkanes to give olefins or oxygenates. 

Supported vanadium catalysts, whereby vanadium oxide is dispersed on a support such as alumina or titania are of particular importance in, for instance, the oxidative dehydrogenation of alkanes [58-64]. Such materials have attracted considerable interest in the direct dehydrogenation of butane, where a key driver is to identify the relationship between catalytic activity and structural properties [5, 6, 65-68]. In the pure (solid) metal oxides the coordination of vanadium is well defined. However, this is not necessarily true in the case of supported catalysts. Vanadium may be present on the support surface as isolated vanadium ions dimeric or polymeric species one- and two-dimensional chains of vanadium ions ... 

Supported VO, catalysts show good catalytic performance in both oxidation and reduction reactions for example, they are among the most active and selective simple metal oxides for dehydrogenation and oxidative dehydrogenation of alkanes. The possibiUty of using oxide systems other than chromia is being... 

A further report of the oxidation ability of manganese nodules is that of Nitta.53 Several reactions were carried out with natural manganese oxide nodules including oxidative dehydrogenations of alkanes and cycloalkanes, reduction of NO, total oxidation of CO, and use in the gettering of metal and mixed metal ions. For example, nodules were found to have a tremendous capacity for adsorption of heavy metals and toxic metals like Pb2+, and Hg2+. in addition, nodules have been used to sequester metals that are present in petroleum fractions that can contain metals like V and Ni. These metals can cause degradation of the fluid cracking catalysts even at levels as low as 1 ppm. 

In this paper we present a comparative study on the ODH of Cg-C alkanes on VAPO-5, MgVAPO-5 and an active and selective V-Mg-0 mixed oxides catalyst. From these results, the importance of the acid-base character of the catalysts, in addition to the presence of redox sites, on the selectivity to olefins from the oxidative dehydrogenation of alkanes Is tentatively proposed. 

Niobium oxide (niobia) is an active catalyst, and can be used as a support for metal nanoparticles or oxides, and it can serve as a promoter in some reactions ([43 5] and references therein). Catalytic applications of niobia include the Fischer-Tropsch synthesis, oxidative dehydrogenation of alkanes, and oxidative coupling of methane. Studies on high-surface-area niobium oxides are complicated by a high degree of complexity because several stable structures (NbO, NbO and Nb O ) exist and the resulting surfaces of high-surface-area niobium oxides are not simple truncations of bulk niobia structures. This is even more so for supported metal oxides when two-dimensional thin films of niobium oxide partially cover a support oxide (Al Oj, SiOj, ZrOj, TiOj, [43]). Nb Oj was also used as a support for V, Cr, Re, Mo, and W oxide overlayers [45, 46]. 

Bimetallic Pt-Sn catalysts are useful commercially, e.g., for hydrocarbon conversion reactions. In many catalysts, Pt-Sn alloys are formed and play an important role in the catalysis. This is particularly true in recent reports of highly selective oxidative dehydrogenation of alkanes [37]. In addition, Pt-Sn alloys have been investigated as electrocatalysts for fuel cells and may have applications as gas sensors. Characterization of the composition and geometric structure of single-crystal Pt-Sn alloy surfaces is important for developing improved correlations of structure with activity and/or selectivity of Pt-Sn catalysts and electrocatalysts. 

The basic sources of petrochemical synthesis are benzene and its homologues. The production of these compounds from petroleum is profitable. In 1996, the world requirements for benzene will grow up to 24-26 million tons per year. Non-oxidizing dehydrogenation of alkanes is a subject of intensive investigation. So, the selection and increase of the assortment of highly effective catalysts for the synthesis of olefins and aromatic hydrocarbons from alkanes are very important for development of this branch of industry. There are three main catalysts for non-oxidized dehydrogenation ... 

As shown above, oxidized diamond exhibited considerable activity in the oxidative dehydrogenation of alkanes, hence further studies on the oxidized diamond supported catalysts were exploited. Nickel-loaded alumina is generally used for the partial oxidation of methane (reaction 5). However, carbon deposition onto the nickel is the major problem in the commercialization of this process. 

As the olefins and to a lesser extent the alkanes are basic one may expect the desorption to be favored by surface basic sites. In other words oxidative dehydrogenation of alkanes is expected to be easier on surface exhibiting basic properties. As a matter of fact the results given in table 5 from ref 41 show that Mg2V207 which is more basic as shown in table 4 is more selective for olefins in propane conversion and to a lesser extent for n-butane and isobutane oxidation reactions than the other two phases. Such a feature is even more pronounced for the samples with excess MgO at least for propane oxidation, samples which were also shown to present higher basicity (table 4). 

Pt, Pd, Ir Au oxidative dehydrogenation of alkanes, n-butene to butadiene, methanol to formaldehyde improved selectivity... 

Oxidative Dehydrogenation of Alkanes on Pristine and Phosphorous-Doped CNTs... 

The energetics predicted may depend on the cluster size used to model this system or on the actual particle size. For oxidative dehydrogenation of alkanes catalyzed by vanadia, it has been shown that the activity per vanadium atom increases with increasing size of the vanadium particle. This is due to reduced electron transfer of oxygen to vanadium on the smaller particle and, hence, to a the lower reducibility of the smaller nano-sized particles . The lower coordination number of vanadium implies that an increase in charge is less easily accommodated on the smaller particle. 

Selective catalysts for the partial oxidation of hydrocarbons, like those leading to bulk chemicals intermediates (aldehydes, ketones, acids, anhydrides) contain transition metaloxides. Typically, these reactions involve the exchange of several electrons (e ) that come from the valence band of the catalyst two electrons in the case of the oxidative dehydrogenation of alkanes, up to 14 electrons in the case of the partial... 

Kung, H. and Kung, M. (1997). Oxidative Dehydrogenation of Alkanes over Vanadium-Magnesium-Oxides, AjPjpZ. Catal. A Gen., 157, pp. 105-116. 

L6pez Nieto, J., Soler, J., Concepcion, R, et al. (1999). Oxidative Dehydrogenation of Alkanes over V-Based Catalysts Influence of Redox Properties on Catalytic Performance, J. Catal., 185, pp. 324-332. 

Solsona, B., Blasco, T., Lopez Nieto, J., et al. (2001). Vanadium Oxide Supported on Mesoporous MCM-41 as Selective Catalysts in the Oxidative Dehydrogenation of Alkanes, J. Catal, 203, pp. 443-452. 

The oxidative dehydrogenation of alkanes to the corresponding alkenes is exothermic and is an alternative to steam cracking, catal5dic cracking, and catalytic dehydrogenation, which are all endothermic, require high temperatures, and lead to coke formation. 

Fosse Hakonsen, S. and Hohnen, A. (2008). Oxidative Dehydrogenation of Alkanes, Handbook of Heterogeneous Catalysis, J. Wiley, New York, pp. 3384—3400. 

Solsona B, Blasco T, Nieto JML, Pena ML, Rey F, Vidal-Moya A (2001) Vanadium oxide supported on mesoporous MCM41 as selective catalysts in the oxidative dehydrogenation of alkanes. J Catal 203 443 52... 

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