Dehydrogenation selectivity

Reaction conditions were lOTorr CgHio, 200Torr H2, and 273-323 K for hydrogenation (400-443 K for dehydrogenation). Selectivity at 448K based on experimentally measured turnover frequencies (lOTorr CsHio, 200Torr H2). 

Alumina Hydrogenation Dehydrogenation Selective oxidation Metathesis... 

In these species, a reaction in which a C -H bond is broken would lead to dehydrogenation. However, breaking a C"-H bond or cleaving a C"-C bond would lead to degradation products. The statistical probabilities of these three processes are proportional to the number of these bonds in the species, which are shown in Table III. They show that these species only differ in the relative number of C -H bonds. If the C"-H and the C-C bond react with equal probability, whereas the C -H bond reacts somewhat faster, combustion would be more likely for ethane than for the other alkanes. Since the reaction conditions, especially temperatures, for the data on Mg2V207 and Mg3(V04)2 were similar, this argument would account for the low dehydrogenation selectivity observed on these two oxides. 

V/y-Al203 of different loadings contained different vanadia species (45). Therefore, the variation in reoxidation heat (and thus dehydrogenation selectivity) could also be interpreted in terms of different properties of different vanadia species. In addition to V/y-AFCb, it has been shown that the vanadia species in V/Si02 also depended on the loading. 

Figure 4.2 Dependence of conjugated dehydrogenation selectivity (1), isoprene yield (2) and total side products yield (3) on isoamylenes and nitrogen mixture rate. T = 553 °C volume ratio C5H1() N2 = 1 10 20% aqueous H202 rate is 0.185 ml/h.

The amount of coke deposited on molybdena/alumina at the time it affords reasonable dehydrogenation selectivity is somewhat variable and depends on the surface area of the alumina support. Carbon contents of selective catalysts have been generally to be in the range of 5 to 20 wt %. 

The high-Bi systems are favorable for dehydrogenation activity. Similarly in a Ti-V-P system/ Ai showed that P2O5 content increases the acidity of the catalyst which favors MA formation from butadiene up to a point, but impedes the dehydrogenation selectivity of butene-1 to the diene (see Fig. 2-12). 

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