Hydrogenolysis product distributions

Methylcyclopentane is a powerful probe molecule for the study of metal surfaces. The product distribution on platinum depends on the following factors particle size 491 reaction conditions 492-494 carbonaceous residues,492,493,495 and the extent of the interface between the metal and the support.492,493,495 The hydrogenolysis rate of methylcyclopentane depends on the hydrogen pressure.496,497 The rate exhibits a maximal value as a function of hydrogen pressure on EuroPt catalysts.498 The hydrogenolysis of methylcyclopentane has also been studied over Pt-Ru bimetallic catalysts.499... 

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

A comparison of various metals as catalysts for the hydrogenolysis of hydrocarbons reveals a wide variation in catalytic activity, even among such closely related metals as the noble metals of group VIII of the periodic table. Striking differences in the distribution of hydrogenolysis products have also been revealed in studies on selected hydrocarbon reactants. These features are emphasized in the following discussion of activity patterns and product distributions in hydrogenolysis. 

Distribution of n-Heptane Hydrogenolysis Products Over Metals (23)... 

Metal Temperature (°C) Percent total conversion Distribution of hydrogenolysis products (Mole percent)6 ... 

The successive demethylation scheme of hydrogenolysis just discussed for iron, cobalt, and nickel clearly does not apply to the noble metals of group VIII. This can be seen by examining the product distribution data in Table IV. The amounts of methane observed are much lower than would be expected if the hydrogenolysis occurred by successive demethylation steps. Thus, we have another indication that the noble and nonnoble metals of group VIII behave as two separate classes with regard to their catalytic properties in the hydrogenolysis of hydrocarbons. 

Adsorption modes and hydrogenolysis were also correlated with other metal-catalyzed reactions. Gault noticed striking similarities in product distributions of isomerization and ring opening of cycloalkanes. Kinetic and tracer studies provided useful data252 268 to arrive at the conclusion that a common surface intermediate is... 

Even though n-hexane is a minority hydrogenolysis product, it is a reliable measure of the degree of hydrogenolysis because of its ease of mass spectro-metric detection and it is not formed in a background reaction with the walls of the reaction chamber. Besides the saturated hydrogenolysis products and benzene, we found the olefinic products cyclohexene, ethylene, and propylene. Cyclohexene is an intermediate in the dehydrogenation to benzene and its various reactions will be discussed separately in the next section. The olefinic product distribution of ethylene propylene cyclohexene benzene is 10 1 0.5 1. 

Most experimental data are reported on the use of Pd-Ti02 catalysts in the hydrogenation. As equation 24 shows, product distribution is considerably affected by the para substituent. The formation of benzyl alcohols is favorable on nonacidic supports while acidic supports promote hydrogenolysis. Hydrogenolysis can also be avoided under strongly acidic conditions in the presence of ethanol. In this case, the product benzyl alcohol readily undergoes dehydration to form benzyl ethyl ether. 

In order to apply ZVI-based dechlorination for site remediation, we have to be sure that no toxic reaction products are produced in the end, and toxic intermediates, if there are any, are degradable. Product distribution is controlled by reaction mechanisms. For the reduction of chlorinated methanes such as carbon tetrachloride (CT), hydrogenolysis, where chlorines are sequentially replaced by hydrogen, takes place in the presence ofZVI (Vogel etal., 1987 Matheson andTratnyek, 1994 Glod etal., 1997) ... 

As discussed in Section IV, Barron et al. (55, 61) found the cyclic mechanism of isomerization to be predominant, perhaps the sole route, on a highly dispersed platinum-alumina (0.2% w/w Pt). The cyclic mechanism was shown to be important also over platinum films and supported platinum of moderate dispersion (>100 A). Here, although the product distributions were very different from that found over the dispersed catalyst, the initial product distributions at 300°C were practically identical in the isomerization and in methylcyclopentane hydrogenolysis. At lower temperatures they were somewhat different as they also were at all temperatures on platinum films. It was suggested that, especially on platinum films, a bond-shift isomerization could accompany the cyclic... 

Results of similar experiments by Gault and his co-workers (93) with a 10-wt % Pt/Al203 catalyst (mean crystallite size 150-200 A) required the assumption that several successive rearrangements took place in the adsorbed phase before desorption. A model was developed in which either a dehydrocy-clization-hydrogenolysis event or a methyl or ethyl shift involving a tertiary atom competed with desorption. By assuming that the isomeric hexanes had the same desorption probability (d) and the different bond-shift processes proceeded with the same chance (r), it was found possible to reproduce the observed initial product distributions with these two independent parameters. In general, values of d 0.5 and t = 0.10-0.20 fitted the results best. As an additional refinement, the ratio of the C2—C3 and C3—C4 bond scission probabilities for methylcyclo-pentane (0) was taken to be 3.3, rather than the statistical value of 2, to improve further the fit. 

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