Surface products of the dissociative adsorption of methane on Pt{1 1 0}-(1×2)

Numerous studies have been made of the mechanism of dissociative methane adsorption on transition metals, but the surface dissociation products have seldom been conclusively identified. Using a supersonic molecular beam system we have identified the methane dissociation products on Pt{1 1 0}-(1×2). In the temperature range 300 to 450 K the stable dissociation fragment at all coverages is methylidyne (CH). Saturation exposure at 370 K has revealed for the first time an ordered c(2×4)-CH overlayer, which saturates at a coverage of 0.25 ML. Under these conditions there is no evidence for C–C coupling even at high coverages. On heating beyond 470 K this species decomposes to gaseous H2 and adsorbed C. After adsorption to high coverages at 500 K evidence is found for C–C coupling.