Hydrogenolysis of ethane, propane, n-butane, and neopentane on the (111) and (110)-(1×2) surfaces of iridium

Article abstract of DOI:10.1021/ja00233a005

Study of the reactions of saturated hydrocarbons with hydrogen on transition-metal surfaces is of considerable technological importance, most notably in connection with the hydroprocessing of petrochemical feedstocks. We have undertaken a fundamental examination of the role of surface structure in the hydrogenolysis of various short-chain alkanes on two oriented single-crystalline surfaces of iridium. The apparent kinetic parameters and the implicated reaction intermediates (i.e. mechanisms) for both propane and neopentane are nearly indistinguishable on the two surfaces. The selectivity for the hydrogenolysis of n-butane on the two surfaces is due to the occurrence of different adsorbed reaction intermediates. It is suggested that the intermediate that leads to the high selectivity for ethane on the Ir(110)-(1×2) surface is a monomuclear metallacycle pentane, the formation of which is sterically forbidden on the (111) surface. The implication of this proposition (i.e. different mechanisms for n-butane hydrogenolysis) for related reactions of saturated hydrocarbons, such as skeletal isomerizationand cyclization, is discussed briefly.