Dynamics of the interaction of O2 withstepped and damaged Ag surfaces

Abstract

The role of defects in catalytic reactions, especially thoseinvolving low rates and high degrees of selectivity, has beendebated ever since the very early days of surface science.However, most studies on gas-surface interaction and chemisorption performed under controlled laboratory conditionshave dealt so far with nearly perfect low-Miller-index surfaces,which are rather unlike the active powders employed ascatalysts in industrial reactors. The failure in reproducingsome chemical reactions, which occur readily under industrialconditions, was therefore often ascribed to the so-calledstructure gap separating the surface science approach from the real industrial conditions. Overcoming this limit withoutlosing control over the experiment at the nanoscopic scale istherefore an issue of pivotal importance. It can be attackedby studying adsorption on either single-crystal surfaces damagedby ion bombardment or on surfaces aligned along high-Miller-index planes. In this paper we shall discuss O2interaction with Ag(410), a vicinal surface of Ag(100) characterized by open (110)-like steps and by (100) terraces.The use of a supersonic molecular beam to dose O2 allowedus to gain information on the interaction of the gas-phase molecules with steps and terraces separately, by selecting theangle of incidence and the impact energy. The open steps turnedout to be active sites for dissociation, while flat Ag(100)planes are unreactive. For molecular adsorption a reduction inthe activation barrier is observed at the steps, while theAg(100) nanoterraces are much less reactive than wide (100)planes. The main results are confirmed by the preliminary investigation of O2/Ag(210).