Hydrogenolysis of linear alkanes

Polystyrene Modification and Hydrogenolysis of Linear Alkanes and Polyethylene 99 Selectivity %... 

Detailed study of the products of the hydrogenolysis of linear alkanes shows two... 

Table 2. Kinetic parameters for the hydrogenolysis of linear alkanes on EUROPT-1 TOF and selectivities at 573 K [6, 15].

Although the C—C—C bond angles in the C5 ring are close to that for tetrahedral carbon, the fission of a C—C bond by hydrogenolysis occurs more readily than that of linear alkanes. Reaction takes place at lower temperatures and with lower activation energies, and the order of reaction in hydrogen (for methylcyclopentane) is positive, where for an acyclic alkane it would be negative. This is... 

Thus, it has been shown that, in SOMC-catalyzed hydrogenolysis on an oxide at low temperature, side phenomena due to adsorption or chain walking could occur. These results with linear alkanes and polymers bring a better understanding of the catalytic activity of the ZrH catalyst. 

In fact, the acid-catalysed ring contraction of alkylcyclohexanes to al-kylcyclopentanes is potentially important as a reaction, because cyclopentanes are more readily ring-opened than alkylcyclohexanes over precious metal hydrogenolysis catalysts to give linear hydrocarbons. Such linear alkanes are suitable for diesel fuel. Addition of an acidic function therefore enables both cyclopentanes and cyclohexanes to be transformed at a similar rate in this way. 

Fresh tungsten carbides catalyze hydrogenolysis of branched (neopentane, 3,3-dimethyl pentane, etc) and linear (hexane, heptane, etc) alkanes at high rates and with high selectivities to lower alkanes (47). The different C—C bonds are cleaved at about an equal rate, and there is negligible isomerization activity. The absence of isomerization products is not the result of rapid secondary hydrogenolysis of the products on the WC surface. Again, the rates and the product distribution are similar to those of Ru. 

Before reviewing reactions of the individual hydrocarbons, some overall trends will be discussed. In general, post-reaction surface analysis by AES showed the presence of submonolayer coverages of carbon, with a fractional coverage fairly independent of reaction conditions for a given alkane. The amount of carbon left on the surface increased approximately linearly with the size of the parent hydrocarbon molecule. This carbon residue is not believed to be an important intermediate in the hydrogenolysis reactions , however,... 

O Total rates of reaction for linear C3—Ce alkanes and neopentane A hydrogenolysis rates only A isomerisation rates only broken line, results for ethane. 

While with linear and singly-branched alkanes there is clear but not extensive evidence that on platinum catalysts the intermediates for isomerisation and for hydrogenolysis differ in their extents of dehydrogenation, with doubly-branched alkanes as exemplified by ncopentane (2,2-dimethylpropane) the situation appears not the same. In an extensive review of Arrhenius parameters for its reactions, activation energies for the two reactions were found to be of the same order, - as were orders of reaction (for Pt/KL and Pt/KY zeolites - ). On EUROPT-1 and on oriented model platinum catalysts, activation energies for total reaction increased markedly with hydrogen pressure, as indeed they should. The two reaction paths thus seem to go via the same intermediate, which might be the ap-diadsorbed species. 

The yield vs. space time plots permit to distinguish primary and secondary products. The formation of dimethylpentanes was found to speed up as space time was increased (not shown). At low conversions (space times) the formation rates of the mono-branched C7 isomers and the cracking products (propane and wo-butane) were independent of the space time as shown by the linear plots in Fig. 3. These results suggest that multi-branched C7 isomers were obtained from the primary product methylhexanes and 3-ethylpenthane [7]. Neither hydrogenolysis products, such as methane and ethane, nor >C alkanes, were formed under the applied conditions. 

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