Theory of C2Hx species on Pt{110} (1x2): reaction pathways for dehydrogenation.

A complete reaction sequence for molecular dissociation at a surface has been characterized using density functional theory. The barriers for sequential ethane dehydrogenation on Pt{110} are found to fall into distinct energy sets: very low barriers, with values in the range of 0.29-0.42 eV, for the initial ethane dissociation to ethene and ethylidene at the surface; medium barriers, in the range of 0.72-1.10 eV, for dehydrogenation of C(2)H(4) fragments to vinylidene and ethyne; and high barriers, requiring more than 1.45 eV, for further dehydrogenation. For dissociation processes where more than one pathway has been found, the lowest energetic route links the most stable reactant adsorbed state at the surface to a product state involving the hydrocarbon moiety adsorbed in its most stable configuration at the surface. Hence there is a clear link between surface stability and kinetics for these species.