Propane hydrogenolysis

At low temperatures on both surfaces, propane hydrogenolysis involves cleavage of a single C—C bond to produce equal amounts of methane and... 

In contrast to propane hydrogenolysis, the Arrhenius plots for cyclopropane hydrogenolysis on both surfaces exhibit no deviations from linearity over the entire temperature range studied, and the reaction orders in both hydrogen and cyclopropane are essentially zero". These results have... 

Ir4(CO)i2 reacts with the surface of MgO to generate surface species in which the tetrahedral metal framework is preserved. The structures obtained after decar-bonylation under H2 at 573 K depend on the degree of hydroxylation of the support The iridium cluster nuclearity of 4 was maintained for a low degree of MgO hydroxylation (MgO pretreated at 973 K), but it increased to 6 when the MgO was highly hydroxylated (MgO pretreated at 573 K) [206, 207]. The activity in propane hydrogenolysis of the tailored catalyst is two orders of magnitude less than that of the conventional catalyst at atmospheric pressure and 200 °C. 

TABLE 7.2. Kinetic Parameters for Propane Hydrogenolysis Over Metal Catalysts... 

Alstrup, L, Petersen, U.E., and Rostrup-Nielsen, J.R. Propane hydrogenolysis on sulfur- and copper-modified nickel catalysts. J. Catal 2000,191, 401-408. 

Silica spheres of controlled pore size (83% of pores between 6-lOnm in radius) were impregnated with aqueous nitrate solutions to give 8%Cu/Si02 SitCo/SiO- and 8%Cu-4%Co/SiO . Temperature-programmed reduction, microproBe analysis and propane hydrogenolysis all indicated that the Cu and Co in the bimetallic catalyst were in intimate contact. In the catalysis of CO hydrogenation rate of CO conversion increased in the sequence ... 

TABLE 2 Activities and selectivities in propane hydrogenolysis at 5Z3K... 

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

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]. 

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. 

From these data, some key information can be drawn in both cases, the couple methane/pentane as well as the couple ethane/butane have similar selectivities. This implies that each couple of products (ethane/butane and methane/pentane) is probably formed via a common intermediate, which is probably related to the hexyl surface intermediate D, which is formed as follows cyclohexane reacts first with the surface via C - H activation to produce a cyclohexyl intermediate A, which then undergoes a second C - H bond activation at the /-position to give the key 1,3-dimetallacyclopentane intermediate B. Concerted electron transfer (a 2+2 retrocychzation) leads to a non-cychc -alkenylidene metal surface complex, C, which under H2 can evolve towards a surface hexyl intermediate D. Then, the surface hexyl species D can lead to all the observed products via the following elementary steps (1) hydrogenolysis into hexane (2) /1-hydride elimination to form 1-hexene, followed by re-insertion to form various hexyl complexes (E and F) or (3) a second carbon-carbon bond cleavage, through a y-C - H bond activation to the metallacyclic intermediate G or H (Scheme 40). Under H2, intermediate G can lead either to pentane/methane or ethane/butane mixtures, while intermediate H would form ethane/butane or propane. 

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. 

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

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