Optimizing Pt/Pd Ratios for Enhanced Low-Temperature Catalytic Oxidation of CO and C₃H₆ on Al₂O₃ Support

This study investigated the impact of diverse Pt–Pd ratios on the activity and performance of DOC. A range of Pt–Pd catalysts with different Pt–Pd ratios and monometallic Pd and Pt catalysts on Al₂O₃ support were evaluated systematically. 0.5%wt PGM was used to avoid the high catalyst costs. The light-off temperatures and conversion efficiencies of CO, NO, and C₃H₆ were investigated under simulated diesel exhaust conditions. Several scientific techniques were used to characterize the catalysts, such as XRD, XPS, H₂-TPR, and CO₂ TPD. The results demonstrated that using bimetallic Pt–Pd catalysts on Al₂O₃ support significantly improved light-off temperatures and conversion efficiency than monometallic Pt and Pd catalysts. The order of light-off temperatures and CO and C₃H₆ conversions was: 0.4Pt0.1Pd < 0.3Pt0.2Pd < 0.2Pt0.3Pd < 0.1Pt0.4Pd < 0.5Pd < 0.5Pt. The synergistic enhancement of catalytic activity can be ascribed to the coexistence of active sites for Pt and Pd. 0.4Pt0.1Pd bimetallic catalyst showed best activity and stability in conversion of CO and C₃H₆ among all catalysts. As a result of the competitive adsorption of C₃H₆ and CO on Pt surface, which restricts the availability of adsorbed oxygen, the monometallic Pt/Al₂O₃ catalyst demonstrated high light-off temperatures and slow CO and C₃H₆ conversion rates. However, the Pd/Al₂O₃ catalyst showed very stable conversion efficiency, demonstrating metallic Pd’s higher stability than Pt/Al₂O₃. Results demonstrated that Pt can be prudently incorporated into Pd-catalysts to improve their catalytic activity. It is noteworthy that the optimal Pt to Pd ratio plays a vital role in balancing activity and stability. The careful use of Pt-modified Pt–Pd bimetallic catalysts holds promise for achieving desired emissions conversion conditions. For instance, the 0.4Pt0.1Pd bimetallic catalysts exhibited superior activity and stability in the conversion of CO and C₃H₆ compared to other bimetallic catalysts. Pt loading above a specific amount may reduce activity due to Pt and Pd active site overlap and saturation.