Application of the Transient Response Technique to the Study of CO + NO + O2 Interaction on CuxCo3-xO4 Catalysts.

NO + CO interaction has been studied in the temperature range 60 to 240°C on the CuxCo3−xO4 spinels, where x = 0.3, 0.54, and 0.94. At temperatures up to the "light-off" temperature, where degrees of surface reduction below 50% of monolayer oxygen are realized, the formation of N2O is an important intermediate: step of the NO + CO reaction. At higher temperatures, degrees of surface reduction up to several monolayers are attained and a route of direct NO reduction to N2 becomes important. On oxidized surfaces large amounts of NO are adsorbed which, however, are inactive towards reduction. Under oxidizing conditions the NO + O2 + CO interaction proceeds with slow reoxidation of the catalyst surface. The activity towards NO reduction even in oxidizing conditions is found to increase with increasing copper content (x). This is attributed to the enhanced capability of catalysts with x ≥ 0.5 to accumulate reduced sites in the surface layer.