Catalytic Activity of C3H8 over Fresh and Aged Pd/Al2O3 Close-Coupled Catalysts

The Pd/Al2O3 close-coupled catalysts supported on modified alumina were prepared by an impregnation method, and then characterized by H2-temperature programmed reduction (H2-TPR), CO chemisorption, and X-ray photoelectron spectroscopy (XPS). Both total catalytic activity and single reactions in related to C3H8 conversion were tested in simulated exhaust gas. The results show that the amount of active PdOx decreases and negative metallic Pd0 appears during aging treatment. The light-off temperature (T50) and complete conversion temperature (T90) increase by 76 °C and 64 °C, respectively. After aging treatment, signifying that the low-temperature activity decreases more obviously than high temperature property. The results of comparison among single reactions indicate that the light-off activity of reactions which occur in atmosphere with the participation of NO but without H2O injection decreases dramatically after the aging treatment. The inhibitive effect of NO on light-off activity and the positive effect of H2O on high temperature property become obvious during the aging treatment.