Hydrogenolysis of cyclohexane over Ir/SiO(2) 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 r...