Hydrogenolysis of propane

Supported metal hydrides of early transition metals catalyze the hydrogenolysis of alkanes at relatively low temperatures (50-150 °C) [29,90-92]. Noteworthy are their differences in product selectivities. For example, the hydrogenolysis of propane in the presence of a large excess of H2 gives a 1 1 mixture of ethane and methane in the case of zirconium hydride, a group 4... 

In the case of zirconiimi hydride, the hydrogenolysis of propane into a 1 1 mixture of methane and ethane is in good agreement with a /1-alkyl transfer as a key step for carbon-carbon bond cleavage (Scheme 21) [90,93]. 

Product Distributions from Hydrogenolysis of Propane and n-Hexane over Nickel Film Catalysts ... 

E.V. Skakunova, M.M. Ermilova, and V.M. Gryaznov, Hydrogenolysis of propane on palladium-ruthenium membrane catalysts, /zv. Akad, Nauk SSSR, Ser, khim, No. 5, 858 (1988). 

The hydrogenolysis of propane has been studied over Ni/Si02 for a particle size range of 2.5 to 21 nm (276). The curve for TOF versus FE is quite similar to curve 6 of Fig. 14, for ethane hydrogenolysis on the same catalyst (275). The selectivities toward ethane or methane did not change with fraction exposed. 

Figure 3.33. Specific reaction rates for the hydrogenolysis of propane on the Ir (HI) surface.

Figure 5.13. Dependence of fiapp on hydrogen pressure for hydrogenolysis of propane and of n-butane on EUROPT-3 (0.3 % R/AI2O3, curves are calculated by eqn. ES5B (see Chapter 13) using constants of best-fit.

Figure 13.9. Dependence on temperature of hydrogen ordars for hydrogenolysis of propane on iron (4), cobalt (3) and nickel (1 and 2) catalysts. ...

TABLE 13.16. Hydrogenolysis of Propane (72 = S2) and of -Butane (Kinetic and Selectivity Parameters) on Pt/Al203 and PtRe/Al203 Catalysts at 603... 

Figure 13.23. Compensation plot of Arrhenius parameters for hydrogenolysis of propane (O) and of n-butane ( ) on Pt/Al203 (EUROPT-3) and PtRe/Al203 (EUROPT-4). The two sets of results (ref. 43, filled points ref. 3, open points) are from independent studies on different batches of catalyst, published respectively in 1989 and 1996.

The hydrogenolysis of propane (1 atm) led to only a mixture of methane and ethane (1 1) at 150 °C, without any observed alkane metathesis catalytic activity (no formation of compounds of >04). The lack of alkane hydrogenolysis activity with ethane confirmed that, under these reaction conditions, Zr-polyalkyls will not undergo an a-alkyl transfer. Nonetheless, under supercritical conditions... 

Engstrom J R, Goodman D W and Weinberg W H 1988 Hydrogenolysis of ethane, propane, n-butane and neopentane... 

This mechanism is general for all alkanes, and for example the hydrogenolysis of isobutane gives methane and propane as the primary products, and overall a 2 1 ratio of methane and ethane at 100% conversion of isobutane. Similarly, neopentane is transformed into a 3 1 methane/ethane mixture (Table 3 and Scheme 22). 

The formation of a stable monobutyl species obtained at 50 °C is also further demonstrated by its hydrogenolysis at higher temperatures. Indeed, treatment under H2 of the grafted surface organometallic complex, Pts[SnBu]jy, at 300 °C for 4 h generates about one butane per Sn along with traces amounts of propane, ethane, and methane. 

Other types of non-micro-channel, non-micro-flow micro reactors were used for catalyst development and testing [51, 52]. A computer-based micro-reactor system was described for investigating heterogeneously catalyzed gas-phase reactions [52]. The micro reactor is a Pyrex glass tube of 8 mm inner diameter and can be operated up to 500 °C and 1 bar. The reactor inner volume is 5-10 ml, the loop cycle is 0.9 ml, and the pump volume adds a further 9 ml. The reactor was used for isomerization of neopentane and n-pentane and the hydrogenolysis of isobutane, n-butane, propane, ethane, and methane at Pt with a catalyst. 

Hydrogenolysis of butane was used to study the catalysis of the RhPt particles in mesoporous silica. This is a test reaction of reforming of alkanes in oil refinery, and methane, ethane, and propane are formed by the cleavage of terminal or central C-C bond (Scheme 1). 

In conclnsion, it was shown that the hydrogenolysis of glycerol in the presence of heterogeneous rhodium-based catalysts yielded mainly either 1,2-, or 1,3-propane diol. Many parameters influenced the activity and the selectivity of the catalysts, particnlarly the presence of metal additives and the initial pH value. 1,2-propanediol can be obtained nearly quantitatively at high pH. Further woik is currently under progress in order to optimize this reaction. 

Above 323 K, the surface hydride catalyzes the hydrogenolysis of neopentane, isobutane, and propane, whereas ethane does not undergo any significant hydrogenolysis. The first step of the reaction is the activation of the C—H bond, whereas the next step is the activation of the C—C bond of the alkyl groups via (l-methyl migration steps. 

These surface hydrides are active catalysts for the hydrogenolysis of alkanes at moderate temperatures. Zirconium hydride can catalyze the hydrogenolysis of neopentane, isobutane, butane, and propane at 323 K but cannot catalyze the hydrogenolysis of ethane.259... 

Schultz and Linden Ind. Eng. Chem. Process Design and Development, 1 (111), 1962] have studied the hydrogenolysis of low molecular weight paraffins in a tubular flow reactor. The kinetics of the propane reaction may be assumed to be first-order in propane in the regime of interest. From the data below determine the reaction rate constants at the indicated temperatures and the activation energy of the reaction. 

The hydrogenolysis of neopentane occurs primarily by breaking of a single C—C bond to produce methane and isobutane as the major reaction products Small amounts of ethane and propane were also produced. The reaction kinetics were similar on the two surfaces, indicating a similar mechanism for both surfaces. 

Hall et al. (63) found that the active species in the hydrogenolysis of cyclopropane are Mo(IV) in reduced M0O3-AI2O3 catalysts. Also, Burwell and Bowman found that the hydrogenolysis of cyclopropane at 100 C (64) and also propane at 300°C (65) occurs over Mo(IV), Mo(II), and Mo(0) catalysts, which were prepared from Mo(CO)g on AI2O3. The average valence state... 

Having set out the properties of tantalum and zirconium hydride toward C-H bond activation of alkanes we now describe the catalytic hydrogenolysis of C-C bonds. It was previously shown in the laboratory that supported-hydrides of group 4 metals, and particularly of zirconium, catalyze the hydrogenolysis of alkanes [21] and even polyethylene [5] into an ultimate composition of methane and ethane. However, to our initial surprise, these zirconium hydrides did not cleave ethane. (=SiO)2Ta-H also catalyzes the hydrogenolysis of acyclic alkanes such as propane, butane, isobutane and neopentane. But, unlike the group 4 metals, it can also cleave ethane [10], Figure 3.7 illustrates this difference of behavior between (=SiO)2Ta(H) and [(=SiO)(4.j,)Zr(H) ], x= or 2). With Ta, propane is completely transformed into methane by successive reactions, while with Zr only equimolar amounts of methane and ethane are obtained. 

Since Zr-H is able both to (i) activate the C-H bonds of alkanes (via cr-bond metathesis) [15, 48] and to carry out their hydrogenolysis (transfer of a least two carbons via a P-alkyl transfer) and (ii) polymerize olefins (via insertion), the ability of such supported Zr-H was tested in the homologation of propane. 

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