Effects of the addition of small quantities of ceria on the catalytic behavior of Pd-only close-coupled catalysts during automobile exhaust elimination

A series of La-Al2O3 supported Pd-Ce close-coupled catalysts were synthesized by a co-adsorption impregnation method and subsequently investigated. In the case of fresh catalysts, the presence of an optimal concentration of ceria obviously promoted the catalytic activity during HC and NOx eliminations, owing to the interaction between the palladium oxide species (PdOx) and CeO2 that improves the oxidation of Pd0 to PdO and enhances the adsorption of nitrite/nitrates and isocyanate intermediate species on the support under reaction conditions. Pd-Ce(2.0)/La-Al2O3 catalyst (where 2.0 is the wt% of CeO2) exhibited the highest catalytic activity for HC and NO eliminations. Following aging at 1100 °C, the operational window for HC and NOx conversions was broadened and the thermal stability of the catalysts was also improved as a result of the presence of an appropriate quantity of ceria (2.0–4.0 wt%). The enhanced interactions between PdOx and CeO2 evidently led to the formation of a Pd-O-Ce system, stabilizing PdOx species with smaller particle sizes at high temperatures. This result is significant since it suggests a means of improving the catalytic performance of Pd-only close-coupled catalysts during automobile exhaust elimination.

Graphical AbstractThe addition of an optimum concentration of ceria during the synthesis of Pd-only close-coupled catalysts by a co-adsorption impregnation method markedly improves the HC/NO conversions and the thermal stability of the Pd-Ce/La-Al2O3 catalyst.Figure optionsDownload full-size imageDownload as PowerPoint slide