Hydrogenolysis of cyclohexane

Table 8 Distribution of Ci or -hexane over Ir/SiOz- to C5 primary products in the hydrogenolysis of cyclohexane -Temp = 200 °C, Hz/Alkane ratio = 50 ...

Since the hydrogenolysis of cyclohexane and cyclohexane derivatives is less probable than the thermodynamically favored dehydrogenation to form aromatic compounds, most studies address hydrogenolysis only in connection with aromati-zation as an unwanted side reaction. An interesting observation by Somorjai showed, however, that hydrogenolysis of cyclohexane to form n-hexane becomes competitive with aromatization on Pt single crystals with increasing kink density.302 On a Pt surface where approximately 30% of the atoms in the steps are in kink positions, benzene and n-hexane are formed in 1 1 ratio. 

B. Dehydrogenation and Hydrogenolysis of Cyclohexane on Platinum Crystal Surfaces at Low Pressures (< 10-4 Torr)... 

In a series of studies, the dehydrogenation and hydrogenolysis of cyclohexane was studied on both the stepped and low Miller index (111) crystal faces of platinum at a surface temperature of 300°C and a hydrogen to cyclohexane ratio of 20 1. While the rates on the stepped and low Miller index surfaces were not very different for the formation of benzene and hexane, the formation of cyclohexene was very structure sensitive, its rate being 100 times greater on the stepped surface than on the (111) crystal face. In Table III mrnnare the initial turnover numbers for the various reactions at low... 

Note that hydrogenolysis of cyclohexane leads to n-hexane with hydrogen and an iridium catalyst." ... 

Unlike some other group VIII metals (S), platinum does not promote hydrogenolysis of cyclohexanes, but dehydrogenation to aromatic hydrocarbons. Cycloheptanes undergo ring contraction and aromatization rather than hydrogenolysis (9-72) (Scheme 1). 

Figure 2.3 The effect of the degree of ruthenium dispersion on its catalytic activity for hydrogenolysis of cyclohexane to lower carbon number alkanes (28). (Solid points represent rates obtained after 10-20 minutes of exposure of the catalyst to reactants open points represent data obtained after 2 hours of exposure.) (Reprinted with permission from Academic Press, Inc.)... 

Finally, Fe-Co alloys prepared by sonochemistry had very high catalytic activity for dehydrogenation and hydrogenolysis of cyclohexane. ... 

The inclusion of tin in an Ir/AlaOs catalyst (5wt.% of each) completely suppressed the hydrogenolysis of cyclohexane, which in its absence gave n-hexane as a major by-product the rate at 526 K was however decreased, but the activation energy fell from 208 to 125 kJ mol. This remarkable and important result... 

Blakely DW, Somoijai GA. The dehydrogenation and hydrogenolysis of cyclohexane and cyclohexene on stepped (high miller index) platinum surfaces. J Catal 1976 42 181-196. 

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