Butane formation

Figure 9.31. Effect of cell potential on the rates of cis- and trans-2-butene and butane formation upon electrochemical reduction of 1-butene on Pd/C/Nafion electrodes at room temperature.35 Reprinted with permission from the American Chemical Society.

The product distribution of the HDS of thiophene over the Mo(lOO) surface is shown in Table III compared with that reported by Kolboe over a MoS catalyst (14). It is clear that the two are very similar ana that our catalyst mimics the MoS catalyst very closely in this respect. An Arrhenius plot fpigure 2) made in the temperature region mentioned above shows that butadiene is the only product whose rate of formation shows true Arrhenius type dependence and yields an activation energy of 14.4 kcal/mole. At high temperatures the rate of butane formation deviates even more sharply than that of the butenes and does so at lower temperatures (9). 

Starting from n-butane, 2-butoxides that rapidly convert to 2-butanone are found over MgCr204 [24]. However, the further oxidation of adsorbed 2-butanone only gives rise to the acetate species, while starting from n-butane, formate species are also observed. This can be explained assuming that sec-butoxides can partly isomerize to rert-butoxides before further oxidation. This implies that the C-O bond formed is partly ionic and the alkyl moiety has the... 

Figure 5A shows that the selectivity towards butane formation (i.e. the rate of formation of butane relative to that of the butenes) decreases as the Co/Mo ratio increases in the unsupported catalysts. Similar results have previously been reported for alumina supported Co-Mo catalysts (37, 38) and this behavior does therefore appear to be a quite general feature of Co-Mo catalysts. The large change in the selectivity is observed (Figure 5B) to be related to a greater promotion of the HDS reaction rate compared... 

Aliphatic dienes undergo three main photochemical pericyclic processes, whose individual efficiencies depend largely on the torsional angle about the central bond in the specific diene conformer which is excited. These are (a) cyclobutene formation, (b) bicyclof 1.1.0] butane formation and (c) [l,5]-hydrogen migration. A fourth process, methylcyclopropene formation, has also been observed in minor amounts in several cases. 

More recent results have provided additional detail on the conformational requirements for bicyclo[1.1.0]butane formation from conjugated dienes158. Hopf and coworkers have shown that high yields of the isomeric bicyclobutane 78 are obtained from irradiation of... 

From observation of the first parts of the butane formation curves (initial time), it appears that the dissociation rate of thiophene is the highest one. 

Sulfur Coverage Deducted from Butane Formation... 

The early suggestion 27 that n-butano is formed from insertion of CH3CH into ethane cannot be correct since NO completely inhibits n-butane formation. Corroborating evidence is that the butanes, -do, -d4, -d6, -dio, expected from the photolysis of C2H8 + C2D8 are not the observed species, The origin of n-butane must be mainly the as-... 

In any chain mechanism the steady-state hypothesis requires that the rate of initiation is equal to the rate of termination. The rate of reaction (5), as given by the rate of butane formation, is therefore also> a measure of the rate of the initiation reaction (1). Lin and Back have also made a study of the kinetics of butane formation, and have deduced from the results information about the initiation process. The conclusions agree with those obtained from the methane measurements. 

The mechanism of the butane formation was shown to be the combination of ethyl radicals. The yield of butane is reduced to nearly zero by the addition of NO to the reaction mixture. This observation has been confirmed by Ausloos et and by Akimoto et This ruled out the insertion of either CH3CH or C2H4 as the source of butane, since NO would not be expected to inhibit these reactions. Furthermore, the isotopic content of the butanes formed in the photolysis of C2H6-C2D6 mixtures was found to be d, d, d, dj and a trace of ethyl radicals which combine to form the n-butane arise from the addition of hydrogen and deuterium atoms to ethylene formed in the photolysis. 

The hydrogenation of carbon dioxide was studied using composite catalysts comprised of Fe-Zn-M (M= Cr, Al, Ga, Zr) catalysts and the HY zeolite, where the methanol synthesis and the methanol-to-gasoline(MTG) reaction are combined. The results show that light olefins are important intermediates for iso-butane formation. In all of the cases, the selectivity of isobutane, which can be used as a reactant in subsequent methyl-tert-butyl ether (MTBE) synthesis, was the highest in hydrocarbons. 

The hydrogenation of carbon dioxide produced iso-butane over Fe-Zn-M/HY (M= Al, Cr, Ga, Zr) composite catalysts with high selectivities. The mechanism of iso-butane formation combines the methanol synthesis reaction and the MTG reaction. The olefins were formed to be important intermediates for iso-butane formation. In order to obtain high selectivity of iso-butane, we found it essential to prepare a composite catalyst which has high activity for methanol synthesis but low activity for the hydrogenation of olefins. 

The hds of thiophen (623-673 K, 1 atm) over sulphided M0O3 was followed as a function of time. Thiophen conversion and butane formation increased to a maximum and then decreased to a steady value (ca. 1 h), whereas butenes increased continuously to steady values. The reaction proceeded by two independent pathways adsorption of thiophen through S followed by hydrogenation to butane adsorption parallel to the catalyst surface followed by hydrogenation via butadiene and S elimination. 

In addition, the (=Si-0)2Tani-H center catalyzed the metathesis of alkanes, an unprecedented process affording higher and lower homologs. For example, in the metathesis of propane to ethane and butanes, formation of four-centered intermediates was postulated (Scheme 51).708 In the first step, the C—11 bond is activated to yield (=Si-0)2Ta I-Prn and (=Si-0)2Tam-Pr ... 

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