Enhancing low-temperature activity and durability of Pd-based diesel oxidation catalysts using ZrO2 supports

We investigated the impact of ZrO 2 on the performance of palladium-based oxidation catalysts with respect to low-temperature activity, hydrothermal stability, and sulfur tolerance. Pd supported on ZrO 2 and SiO 2 were synthesized for a comparative study. Additionally, in an attempt to maximize the ZrO 2 surface area and improve sulfur tolerance, a Pd support with ZrO 2 -dispersed onto SiO 2 was studied. The physicochemical properties of the catalysts were examined using ICP, N 2 sorption, XRD, SEM, TEM, and NH 3 -, CO 2 -, and NO x -TPD. The activity of the Pd catalysts were measured from 60 to 600 °C in a flow of 4000 ppm CO, 500 ppm NO, 1000 ppm C 3 H 6 , 4% O 2 , 5% H 2 O, and Ar balance. The Pd catalysts were evaluated in fresh, sulfated, and hydrothermally aged states. Overall, the ZrO 2 -containing catalysts showed considerably higher CO and C 3 H 6 oxidation activity than Pd/SiO 2 under the reaction conditions studied. The good performance of ZrO 2 -containing catalysts appeared to be due in part to high Pd dispersion resulting from strong Pd and support interaction. Another beneficial effect of strong interaction between Pd and ZrO 2 was manifested as a greater hydrothermal stability with good oxidation activity even after aging at 800 and 900 °C for 16 h. In contrast, Pd/SiO 2 suffered significant performance loss due to Pd particle coarsening. Although the Pd/ZrO 2 -SiO 2 catalyst was not more active than Pd/ZrO 2 , improved tolerance to sulfur was realized. Unlike the bulk ZrO 2 support, the ZrO 2 -incorporated SiO 2 presented only weak basicity leading to a superior sulfur tolerance of Pd/ZrO 2 -SiO 2 . These results confirmed the potential of developing Pd-based oxidation catalysts with enhanced low-temperature activity and durability using ZrO 2 -SiO 2 supports. Controlling morphology and accessible area of the dispersed ZrO 2 layer appeared critical to further maximize the catalytic performance.