Interaction of ethylene and oxygen with stepped Ag surfaces

The active role of defects in some catalytic reactions was predicted in the very early days of surface science. Most of the studies on gas adsorption at solid surfaces dealt, however, so far with nearly perfect low Miller index surfaces, which are rather unlike the active powders employed as catalysts in industrial reactors. The structure gap between the systems studied by surface scientists and the surface structure of real catalyst powders was therefore often indicated as the reason for the failure in reproducing some chemical reactions, which occur readily in industrial reactors, also in controlled conditions. Overcoming this limit without losing control over the experiment at the nanoscopic level is therefore an issue of pivotal importance, which could be addressed only now that the understanding of adsorption processes at flat surfaces is reasonably established. In this paper we shall review our most recent results on O-2 and C2H4 interaction with Ag(410) and Ag(210), which are vicinal surfaces of Ag(100) characterised by open (110)-like steps and narrow (100) terraces. The gases were dosed with a supersonic molecular beam, allowing to perform experiments at selected and well defined angles of incidence of the gas-phase particles. For both gases we find that the open steps affect gas-surface interaction considerably, changing the energy barriers to adsorption as well as the final chemisorption state.