The mechanism of NO reduction on copper in the presence of oxygen and
isobutene was studied at T = 770 K, under reducing conditions. Mass sp
ectroscopy was used to identify gas-phase intermediates and reaction p
roducts, One intermediate species resulting from the partial oxidation
of isobutene was shown to be active in the NO conversion. X-ray photo
electron spectroscopy was used to analyze the copper surface at differ
ent stages of the reaction. Our conclusion is that oxygen first activa
tes the surface, by forming coexisting phases of Cu2O and CuO. The cop
per surface is then reduced by the hydrocarbon, leading to Cu+ in majo
rity, and to the formation of an active intermediate. At last, the red
uction of NO proceeds rapidly on a zero-valent copper surface together
with consumption of the previously formed intermediate. At the end of
the reaction, the surface is poisoned by carbon.