Hydrogenolysis of cyclohexane over Ir/SiO₂ catalyst: A mechanistic study of carbon-carbon bond cleavage on metallic surfaces

The hydrogenolysis of cyclohexane catalyzed by supported Ir/SiO₂ has been studied to get mechanistic information on the elementary steps of C-C bond cleavage for cyclic saturated hydrocarbons. The reaction was studied under conditions in which no dehydrogenation to benzene occurs. When a mixture of cyclohexane and H₂ flows over a Ir/SiO₂ catalyst at 200°C and for a H₂/cyclohexane ratio superior to 40, methane, ethane, propane, n-butane, n-pentane, and n-hexane are identified to be primary products. The hydrogenolysis of ethane and n-hexane has also been studied to clarify several mechanistic questions. To account for the primary products in the above reactions, a mechanism is proposed in which the key step of the carbon-carbon bond cleavage occurs via concerted electronic transfer in dimetallacyclopentane intermediate. The comparison of product distributions in the hydrogenolysis of cyclohexane and that observed for n-hexane led to conclusions about the relative ease of carbon-carbon bond cleavage with respect to surface alkyl isomerization.