The Application Of Pd/CeO₂Catalyst In Diesel Oxidation Catalysis

Comparing with the gasoline vehicle, diesel vehicle is more energetic efficientand more environmental beneficial, which attaches more and more public attentionsnowadays. However, the exhaust emission of diesel vehicle is becoming into the edge,in which, the particulate matter emission of diesel vehicle is the most important part.Diesel particulate filter （DPF） is the most efficient system to deal with particulatematter emission, and one of its key problems is the regeneration of the fliter. In thiscase, the catalytic assisted fuel combustion was considered as an efficient technology,in which the oxidation catalyst was used to facilitate the combustion of injected fuel.Since Palladium shows good performance, high durability and relative low price, itwas widely used in the field of catalytic combustion/oxidation. What’s more, somerecent work suggests that the addition of CeO₂further improve the activity of Pdbased catalyst. In this work, the C₁₀H₂₂combustion under a simulated diesel exhaustatmosphere was studied, which is aming to provide the technical support to theapplication of oxidation catalyst in the regeneration of diesel particulate filter.The results indicated that Pd loading seriously influence the preferred reaction inthe reaction gas mixture. This induces an abnormal trend that, as Pd loading ratioincreases, the activity of C₁₀H₂₂oxidation decreases and the activities of CO and C₃H₆still increase. This trend induces that the active site of these reactant are different, thesmall and oxidized Pd particle facilitates C₁₀H₂₂oxidation, while the large andmetallic surface Pd atoms facilitate the CO and C₃H₆oxidations.Combine the investigations of surface species and gaseous products, C₁₀H₂₂ignition is found to be suppressed by the accumulation of surface carbonates.1%Pdloading induces the less amount of strong basic site than any other samples. On theother hand, the strong adsorption of C₃H₆on reduced Pd surface atoms suppressedC₁₀H₂₂oxidation. These phenomena were found on3\5\7PC-h, but not on1PC-hbecause that the surface Pd atoms are difficult to be reduced, which hinders C₃H₆adsorption. The above differences between1PC-h and other samples induces that, theC₁₀H₂₂combustion on1PC-h is not sensitive to the gaseous CO₂and C₃H₆, but thereaction on other samples are seriously suppressed by CO₂and C₃H₆.After all, comparing with the conventional Pd/Al₂O₃catalyst, Pd/CeO₂showsgood performance in C₁₀H₂₂combustion and CO and C₃H₆oxidation under oxygen-rich atmosphere. This shows the potential of Pd/CeO2catalysts in assistingthe regeneration of diesel particulate filter by catalytic fuel combustion. However, Pdloading condition seriously influences the preferential reaction in gas mixtures, whichdemands the controllable catalyst preparation, and makes it possible to fulfill the DPFregeneration under different reaction gas atmosphere.