Reduction of NO on copper and its poisoning by SO_2, a mechanistic study

摘要

A combination of catalytic tests and surface studies has been undertaken to better understand the poisoning effect of sulfur dioxide upon the eduction of NO by a hydrocarbon. THe characterization f the copper surface by photoelectron spectroscopy, at various stages of the reaction, made clear an initial oxidation of the catalyst accompanied by the formation of an oxygnerated intermediate; it is followed by a reduction of the surface and a rapid reation of NO with this species. In situ surface infrared measurements have been made on a odel copper surface, Cu(110), under 10~-5 Torr of SO_2 or SO_2 + O_2 revealing the foramtion of molecular adsorbed compounds when the surface is oxidized, slightly covered with oxygen or hydroxylated. SO_2 is a drastic posison o fhte catalytic NO reduction; it reacts with the oxidized surface leading to sulfite and sulfate groups. it intercts with water, leading to hydrogenosulfoxide adsorbates which can obviously block a number of surface sites. It also dissociates on the metallic copper and occupies surface sites. It des not block the hydrocarbon adsorption completely but severely reduces the formation of the active intermediate.