Energetics of C-C bond scission in ethane hydrogenolysis: A theoretical study of possible intermediates and reaction pathways

C-C bond scission steps, which are often considered as rate-determining in ethane hydrogenolysis, are studied by the Unity Bond Index-Quadratic Expone ntial UBI-QEP method. The binding energies of atomic carbon with Group VIII and IB metal surfaces Ni(111), Pd(ll I), Pt(111), Rh(111), Ru(001), Ir(111 ), Fe(110), Cu(111), and Au(111) are estimated using experimental data on t he adsorption of various species on these surfaces. These estimates are cor rected using data from density functional theory (DFT) on the adsorption he ats of the CHx species, Metal surfaces art: arranged in the following serie s according to the binding strength of a carbon atom: Cu(111)<Au(111) < Pd( 111) < Ru(001)<approximate to> Pt(111) < Ni(111) <approximate to> Rh(111) < Ir(111) < Fe(110). The values of chemisorption heats range from 121 kcal/m ol for Au(111) to 193 kcal/mol for Fe(110). The activity of these surfaces toward C-C bond scission increases in the same series. The results of this work suggest that the most probable C-C bond scission precursors are ethyl, ethylidyne, adsorbed acetylene, CH2CH, CH2C, and CHC. Theoretical data obt ained by different methods are compared and found to agree well with each o ther. An overview of experimental data on ethane hydrogenolysis mechanisms is given.