Effective control of hydrocarbon (HC) emissions at low temperatures is critical for emission compliance, since a large fraction (typically 70–80%) of tailpipe HC emissions occurs during the first couple of minutes after an engine cold-start. The oxidation of propane, iso-pentane and propylene was investigated over Pd-only, Pt-only and Pt–Pd catalysts aged under lean-rich cycling conditions. Various characterizations such as XRD, XANES, STEM, CO chemisorption and H₂-TPR were performed over the initial catalysts. Moreover, before and after the reaction, the states of the catalysts were characterized by XRD, XANES and STEM. The oxidation activity tests were carried out under both near-stoichiometric and fully lean conditions in the feedstream containing HC, O₂, CO, H₂, NO and H₂O. Under the near-stoichiometric condition, the Pt/Al₂O₃ catalyst showed much higher activity for propane oxidation than the Pd/Al₂O₃ and Pt–Pd/Al₂O₃ catalysts. For propylene oxidation, on the other hand, the Pd/Al₂O₃ catalyst was the most active, and the Pt/Al₂O₃ catalyst exhibited the lowest activity due to the fact that the co-presence of CO and propylene on the Pt surface leads to their competition for a limited amount of adsorbed oxygen. Under the fully lean condition, metallic Pd in the Pd/Al₂O₃ catalyst was gradually oxidized to PdO and consequently poisoned by H₂O, whereas there was little change in the state of the Pt/Al₂O₃ catalyst, indicating higher stability of metallic Pt than Pd. However, a drastic decrease in the propane oxidation activity was observed over Pt/Al₂O₃ in the presence of excess oxygen in the fully lean feed since preferential adsorption of oxygen on the Pt surface inhibited propane adsorption and thus the oxidation reaction. In addition, the propylene oxidation activity under the fully lean condition was greatly enhanced over all three catalysts compared to that observed under the near-stoichiometric condition, with Pd/Al₂O₃ still being more active than Pt/Al₂O₃. The catalyst activity for iso-pentane oxidation was affected only to a relatively small extent by the high oxygen concentration, so that the same activity order among the catalysts (Pt > Pt–Pd > Pd) was observed under both the slightly lean and fully lean conditions. These results indicate that both hydrocarbon type and oxygen concentration level are important factors determining the relative oxidation activities of the various noble metal catalysts. Relatively small beneficial effects of Pt–Pd alloying were observed during iso-pentane oxidation at low temperatures under the near-stoichiometric conditions and during propane oxidation at high temperatures under the fully lean condition. However, alloy formation was found to be detrimental for the propane oxidation under the slightly lean condition.

低温下有效控制碳氢化合物（HC）排放对于遵守排放标准至关重要，因为在发动机冷启动后的前几分钟内，大部分排气管HC排放（通常为70-80％）会发生。丙烷，异戊烷和丙烯的氧化是通过在贫油循环条件下老化的仅Pd，Pt和Pt-Pd催化剂进行的。在初始催化剂上进行了各种表征，如XRD，XANES，STEM，CO化学吸附和H ₂ -TPR。此外，在反应之前和之后，通过XRD，XANES和STEM表征催化剂的状态。在含有HC，O ₂，CO，H ₂的进料流中，在接近化学计量的条件和完全稀的条件下进行了氧化活性测试，NO和H ₂ O.根据接近化学计量条件下，在Pt / Al的₂ ö ₃催化剂显示出高得多的活性丙烷氧化比的Pd / Al的₂ ö ₃和铂-钯/ Al的_2种ö ₃催化剂。另一方面，对于丙烯氧化，Pd / Al ₂ O ₃催化剂是最活泼的，而Pt / Al ₂ O ₃催化剂则表现出最低的活性，这是由于CO和丙烯在催化剂表面同时存在。 Pt表面导致它们竞争有限数量的吸附氧。在完全贫化的条件下，Pd / Al ₂ O ₃中的金属Pd催化剂逐渐被氧化为PdO，并因此被H ₂ O中毒，而Pt / Al ₂ O ₃催化剂的状态变化很小，表明金属Pt的稳定性高于Pd。然而，在完全贫化的进料中存在过量氧气的情况下，观察到丙烷氧化活性比Pt / Al ₂ O ₃急剧降低，因为在Pt表面上优先吸附氧气会抑制丙烷的吸附，从而抑制了氧化反应。此外，与在Pd / Al ₂ O ₃的近化学计量条件下观察到的相比，在所有三种催化剂下完全贫化条件下的丙烯氧化活性都大大提高了。仍然比Pt / Al ₂ O ₃更加活跃。高氧浓度对异戊烷氧化的催化剂活性影响相对较小，因此在轻度和完全稀薄状态下，催化剂之间的活性顺序相同（Pt> Pt–Pd> Pd）。情况。这些结果表明，烃类型和氧浓度水平都是决定各种贵金属催化剂的相对氧化活性的重要因素。Pt-Pd合金化的相对较小的有益作用在接近化学计量比的低温下在异戊烷氧化过程中以及在完全稀薄的条件下在高温下的丙烷氧化过程中观察到。然而，发现合金的形成对于在稍微贫化的条件下的丙烷氧化是有害的。