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 s tudied to get mechanistic information on the elementary steps of C-C bond c leavage for cyclic saturated hydrocarbons. The reaction was studied under c onditions in which no dehydrogenation to benzene occurs. When a mixture of cyclohexane and H-2 flows over a IR/SiO2 catalyst at 200 degreesC and for a H-2/cyclohexane ratio superior to 40, methane, ethane, propane, n-butane, n-pentane, and n-hexane are identified to be primary products. The hydrogen olysis of ethane and n-hexane has also been studied to clarify several mech anistic questions. To account for the primary products in the above reactio ns, 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 hydrogenolysi s of cyclohexane and that observed for n-hexane led to conclusions about th e relative ease of carbon-carbon bond cleavage with respect to surface alky l isomerization.