PHYSICOCHEMICAL PROPERTIES OF CE-CONTAINING 3-WAY CATALYSTS AND THE EFFECT OF CE ON CATALYST ACTIVITY

The activity of Pt,Rh,Ce/γ-Al2O3 and Pt,Rh/CeO2 catalysts has been studied in a full complement synthetic exhaust gas mixture consisting of H2, CO, C3H6, C3H8, NO, O2, N2, CO2, H2O, and SO2. Direct interaction between Pt and CeO2 was shown to lead to large improvements in catalyst performance after activation of the catalyst in the synthetic exhaust gas. Catalyst activation was shown to be due to reduction of the noble metals and surface Ce and this state of the catalyst was found to be particularly effective for CO oxidation. The key component responsible for activation was shown to be H2; even at the low H2 level present in the exhaust gas (≤.26 vol%), reduction is shown to be very easy. The degree of Pt/Ce interaction, and thus activity, after catalyst activation could be controlled by varying the CeO2 crystallite size. Decreasing the CeO2 crystallite size led to greater Pt/Ce interaction as shown by TPR and STEM analysis and resulted in greater activity for both fresh and laboratory aged catalysts. Direct Pt/Ce interaction also led to a synergistic reduction of Pt and surface Ce which we found to qualitatively correlate with catalyst performance after activation. © 1992.