少量CeO2的添加对Pd/La-Al2O3密偶催化剂三效性能的影响

以La改性的Al₂O₃为载体，采用共吸附浸渍法制备了一系列不同CeO₂含量的单Pd密偶催化剂，并对其进行了表征. PdO_x和CeO₂之间的强相互作用改善了Pd⁰再氧化为PdO的能力，同时增强了反应条件下硝酸盐，亚硝酸盐和异氰酸盐在载体上的吸附. 因此适量CeO₂的添加明显改善了新鲜催化剂对HC和NO_x的催化性能，且当CeO₂添加量为2%时催化效果最佳. Pd-Ce界面上PdO_x和CeO₂间强相互作用也使得PdO_x物种在高温时仍能以小颗粒的形式分散在载体上，从而显著地提高催化剂的热稳定性. 经1100 ℃高温老化后，CeO₂ （2%-4%）的存在明显拓宽了HC和NO_x的操作窗口，这对于提高单Pd密偶催化剂在汽车尾气处理上的催化性能有重要意义.

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 NO_x eliminations, owing to the interaction between the palladium oxide species (PdO_x) 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 ℃, the operational window for HC and NO_x 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 PdO_x and CeO₂ evidently led to the formation of a Pd-O-Ce system, stabilizing PdO_x 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.