Hydrogenolysis on metals

The simplest hydrocarbon hydrogenolysis reaction is that with ethane which can yield methane as the sole reaction product. On the other hand, with larger molecules a range of reaction products is possible since the adsorbed reactant may fragment at more than one C—C bond and, furthermore, even if only one such bond is broken in the reaction of a given molecule, the reactant will often contain more than one stereochemically distinguishable type of C—C bond. 

Initial Products from Hydrogertolysis on Thick Polycrystalline Nickel Films 

Platinum is an important example of a metal where, even on an uncontaminated surface such as is offered by an evaporated film, there is a strong tendency for only one C—C bond to be ruptured in any particular reacting molecule. On this basis, one may express the distribution of reaction products in terms of relative C—C bond rupture probabilities. Some data of this sort are contained in Table XI for thick and ultrathin film catalysts, and for comparison there are included some data for reactions on a silica-supported catalyst containing 0.8% platinum. These data all refer to reactions carried out in the presence of a large excess of hydrogen, although the results of Kikuchi et al. (128) indicate that on platinum catalysts the position of C—C bond rupture (in n-pentane) is very little dependent on hydrogen pressure. The data in Table XI show that, on the whole, the 0.8% platinum/silica catalyst used by Matsumoto et al. (110) was inter- 

Relative C—C Bond Rupture Probabilities on Platinum Catalysts 

Bond rupture probabilities have also been reported by Myers and Munns (160) for hydrogenolysis reactions over a number of supported catalysts containing platinum in the range 0.1-1%. The reactions were carried out in the region of 350°-480°C. Provided one confines the comparison to nonacidic supports, these results are in tolerable agreement with the data in Table XI. 

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Fig. 14 Hydrogenolysis on metal catalysts product from ring opening reactions of Cl ring contraction compounds and their corresponding research octane number and motor octane number. Adapted from ref. 100.

Sinfelt JH (1991) Catalytic hydrogenolysis on metals. Catal Lett 9 159... 

J.H. Sinfelt. Catalytic Hydrogenolysis on Metals. Catal. Lett. 9 159 (1991). 

Since most of the phase transfer reactions useful for synthesis are reviewed in Ch. 4, this section will contain only a few examples of hydrogenation or hydrogenolysis on metallic catalysts. 

In some catalytic processes, it is necessary to avoid carbon-carbon bond cleavage. For example, isobutane is mainly transformed into its lower alkane homologues (hydrogenolysis products) on metal surfaces, while it can be converted more and more selectively into isobutene when the Pt catalysts contain an increasing amount of Sn (selective dehydrogenation process) [131]. 

Hydrogenolysis reactions of hydrocarbons on metal catalysts have been investigated in some detail. Extensive studies have been conducted on both alkanes and cycloalkanes. While a number of questions still remain with regard to mechanistic and kinetic details of the reactions, the general features seem reasonably clear. 

Kinetic Parameters for Ethane Hydrogenolysis on Silica-Supported Metals (16)... 

The concept of site isolation is important in catalysis. On metal particles one usually assumes that ensembles of metal atoms are necessary to activate bonds and to accommodate the fragments of molecules that tend to dissociate or to recombine. We present here three examples of such effects the dehydrogenation of decane into 1-decene, the dehydrogenation of isobutane into isobutene and the hydrogenolysis of acids or esters into aldehydes and alcohols. In most cases the effect of tin, present as a surface alloy, wiU be to dilute the active sites, reducing thereby the yield of competitive reactions. 

THE ilECHANISM OF HYDROGENOLYSIS AND ISOMERIZATION OF OXACYCLOALKANES ON METALS, PART X ... 

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