Activation of methane on iron, nickel, and platinum surfaces: a molecular orbital study

Surface metal atom insertion into methane CH bonds (oxidative addition) has been studied for Fe(100), rough Fe(100), Fe(110), Ni(100), Ni(111), and Pt(111) surfaces by using ASED molecular orbital theory and cluster models. All transition states have in common CH stretches of 0.4-0.5 A and three-centered metal--carbon, metal--hydrogen, and C--H bonding derived from two methane sigma orbitals, the empty sigma *, and metal s + d band orbitals. For Fe, the predicted order of activity is rough Fe(100) > Fe(100) > Fe(110) and for Ni the order is Ni(100) > Ni(111). The higher barriers for the more closely packed surfaces are found to be related to the stronger metal bonds in these surfaces. The calculated activation energies on Ni(100) and Ni(111) are close to recent experimental determinations, and a low value obtained for Pt(111) suggests more experiments are needed. 19 ref.--AA