Butane oxidative dehydrogenation

Effects of cesium doping on the kinetics and mechanism of the n-butane oxidative dehydrogenation over nickel molybdate catalysts... 

Madeira, L.M., Herrmann, J.M., Disdier, J., Portela, M.R, and Ereire, E.G. New evidences of redox mechanism in -butane oxidative dehydrogenation over undoped and Cs-doped nickel molybdates. Appl. Catal. A Gen. 2002, 235, 1. 

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). 

O-X-D [Oxidative dehydrogenation] A process for converting n-butane to butadiene by selective atmospheric oxidation over a catalyst. Developed by the Phillips Petroleum Company and used by that company in Texas from 1971 to 1976. See also Oxo-D. 

Rives et al. reported the use of Mg/V mixed oxides obtained from V(III)-substituted LDH precursors as catalysts for the oxidative dehydrogenation of propane and -butane [71]. Their results indicated that the relative amounts of Mg3V04 and MgO, which depend on the V(III) content of the starting LDHs, determine the performance of the catalysts. 

Figure 3. Differential heat of reoxidation and selectivity for oxidative dehydrogenation of butane on V2O5/Y-AI2O3 samples, a 8.2 V/nm sample, reaction at 400°C and b 2.9 V/nm sample, reaction at 480°C.

Figure 4. Dependence of selectivity for oxidative dehydrogenation of butane over orthovanadates on the reduction potential of the cations. Reaction conditions 500°C, butane/Oz/He = 4/8/88, butane conversion = 12.5%.

The data in Figs. 3 and 4 show that the ease of removal of a lattice oxygen, which can also be expressed in terms of the reducibility of the neighboring cations, has a strong effect on the selectivity for oxidative dehydrogenation of butane. If this is the only factor that determines selectivity, then a catalyst that is selective for dehydrogenation of butane, such as Mg3(V04)2, will be selective for other alkanes as well. Likewise, any catalyst that contains bonds will not be... 

M-butane proceeds via an intermolecular mechanism with 2-butene involved intermediately.300-303 The role of the transition metal promoters such as Fe and Mn was shown to increase the surface concentration of the intermediate butene 304 The formation of butene is speculated to occur through an oxidative dehydrogenation on the metal site305 or by one-electron oxidation.306... 

Other catalysts for alkane oxidative dehydrogenation have also been reported in the patent literature. For example, it was claimed that a Na and Li phosphomolybdate produced 17% butadiene and 5% butenes at 600°C with a 1 1 mixture of butane and oxygen (13). 

There are fewer studies of oxidative dehydrogenation of butane, and even fewer for cyclohexane than ethane or propane. The performance of the better catalysts in these two reactions are summarized in Table VII and Fig. 5. Because of the larger number of secondary carbon atoms in these molecules, they are more reactive with gaseous oxygen than the smaller alkanes. In ex-... 

Fig. 5. Selectivity for oxidative dehydrogenation of cyclohexane and butane. Data taken from Table 7.

As to the method of preparation, it was found that V-Mg oxide catalysts prepared with a Mg(OH)2 precursor that was precipitated with KOH was less selective than one prepared with a MgC03 purecursor precipitated with (NH4)2C03 (25). Interestingly, unlike the butane reaction, there was no effect of preparation on the oxidative dehydrogenation of propane using the same catalysts, as mentioned earlier (25, 30). Unlike the oxidation of propane, Mg pyrovanadate was nonselective for butane (25, 26). Mg metavanadate was nonselective as well (26). 

Fig. 7. Differential heat of reoxidation and selectivity for oxidative dehydrogenation of butane on V2Ov y -AFO, samples. For the 2.9 V/nm2 sample, the selectivity was calculated for the detected gaseous products, (a) 8.2 V/nm2 sample, reaction at 400°C (b) 2.9 V/ntn2 sample, reaction at 480°C (c) 8.2 V/nm2 sample, reduction by CO at 530°C, butane reaction at 400°C and (d) 2.9 V/nm2 sample, reduction by CO at 400°C, butane reaction at 480°C. (a) and (b) are from Ref. 50 (c) and (d) and from P. J., Andersen, Ph D. thesis, Northwestern University, 1992.

The additional requirement of the size of molecule with respect to the V — V distance in the active site is perhaps the reason behind the fact that propane and butane show not only different selectivity behavior, but also different dependence of the selectivity on the reducibility of the catalyst the selectivity for dehydrogenation in butane oxidation decreases rapidly with increasing reducibility of the catalyst (Figs. 6 and 7), but the selectivity in propane oxidation is much less dependent on it (31). 

After this paper was accepted for publication in November, 1992, a number of reports have appeared that deal with the subject of oxidative dehydrogenation of light alkanes. The effect of the structure of vanadia on a support has been investigated for the oxidation of butane [87J and propane [88-90], The evidence supports the concepts that the bridging oxygen in V — O — V plays an important role in the oxidation reaction [87, 90], The data also show that vanadia species of different structures on these supports have different catalytic properties, and that isolated V04 units are the most selective [91]. 

Spinel oxides with a general formula AB2O4 (i.e. the so-called normal spinels) are important materials in industrial catalysis. They are thermally stable and maintain enhanced and sustained activities for a variety of industrially important reactions including decomposition of nitrous oxide [1], oxidation and dehydrogenation of hydrocarbons [2], low temperature methanol synthesis [3], oxidation of carbon monoxide and hydrocarbon [4], and oxidative dehydrogenation of butanes [5]. A major problem in the applications of this class of compound as catalyst, however, lies in their usually low specific surface area [6]. 

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