Study of active species of Cu-K/ZrO2 catalysts involved in the oxidation of soot

The effect of the deposition of Cu and K elements on zirconia was studied in the oxidation of a carbon black (CB), considered as a model of diesel soot. Catalytic tests were carried out using CB–catalyst mixtures prepared under loose and tight contact conditions. The potassium-containing catalysts exhibited high activity in loose contact that differed slightly from that obtained in tight contact. The introduction of both Cu and K on ZrO2 provided synergistic effects in the CB oxidation. It is proposed that these systems can release active oxygen species to oxidize CB even in the absence of gaseous oxygen. Consequently, (CB–catalyst) loose contact mixtures treated at different temperatures under Ar flow were characterized by electron paramagnetic resonance and temperature-programmed reduction measurements. The presence of potassium favours contact between the catalyst and CB and enhances the catalyst's ability to release active oxygen species. In K/ZrO2, it yields an increase in the amount of Zr3+ ions, which appear to be stabilized mainly in monoclinic ZrO2. In Cu-K/ZrO2 catalysts, the potassium promoter preferentially interacts with the supported copper(II) species and favours their participation following a redox mechanism.