REDUCTION OF NO BY CO OVER RH CEO2-ZRO2 CATALYSTS - EVIDENCE FOR A SUPPORT-PROMOTED CATALYTIC ACTIVITY/

Reduction of NO by CO catalysed by Rh/CeO2-ZrO2 solid solutions is inv estigated with the aim to elucidate the role of the CeO2-ZrO2 supports in modifying the activity of supported Rh. Two distinct kinetic regim es, characterised by different activation energies are observed below and above 500 K. It is proposed that below 500 K the reduction of NO o ccurs at the expenses of a concomitant oxidation of Ce3+ sites. In thi s model, the supported metal activates the reducing agent favouring th e efficiency of Ce4+/Ce3+ redox couple. The influence of a high temper ature reduction (H-2, 1073 K) is also investigated. Such a treatment, which increases the reducibility at low temperatures of the CeO2-ZrO2 solid solution, promotes the efficiency of the catalysts at low temper atures, confirming the important role of the Ce4+/Ce3+ redox couple in determining the activity of the catalyst. (C) 1998 Academic Press.