Pd(100)氧化表面上低温丙烷氧化的活性相研究  

Active Phase on Oxidized Pd(100)for Low-Temperature Propane Oxidation

作　　者：徐美佳 张宇琛 朱一帆 李昌林 吴子昂 周雄 吴凯[1] Meijia Xu;Yuchen Zhang;Yifan Zhu;Changlin Li;Zi-Ang Wu;Xiong Zhou;Kai Wu(College of Chemistry and Molecular Engineering,Peking University,Beijing 100871,China)

机构地区：[1]北京大学化学与分子工程学院,北京100871

出　　处：《物理化学学报》2023年第10期11-18,共8页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(22222102,21821004,21927901)资助项目。

摘　　要：钯作为汽车尾气处理的三效催化剂的关键成分,在烷烃的完全氧化和CO低温氧化中扮演着重要催化角色。在富氧环境下,钯表面通常会形成薄的氧化物层。为了揭示钯表面上烷烃完全氧化的活性相,我们对Pd(100)表面氧化过程及其对丙烷氧化的活性相进行了详细研究。实验结果表明,在不同氧化条件下,Pd(100)表面依次形成了三种单层氧化相,即(2×2)-O、(5×5)-PdO和(√5×√5)R27°-PdO,它们的O覆盖度分别为0.25单层,0.56单层和0.8单层。值得注意的是,(5×5)-PdO结构首次得到了高分辨扫描隧道显微镜成像的确认。实验发现该结构呈现出典型的手性特征,两种手性对映体结构也可在实验中观察到。根据高分辨原子成像,我们提出了新的(5×5)-PdO结构模型。(5×5)-PdO结构的手性特征在手性催化等领域中可能有着重要意义。热分解实验发现(5×5)-PdO结构热分解形成(√5×√5)R27°-PdO和(2×2)-O结构,而(√5×√5)R27°-PdO热分解产生(2×2)-O。该结果表明这些氧化相的热稳定性次序为(2×2)-O>(√5×√5)R27°-PdO>(5×5)-PdO。随后我们对比研究了这三种氧化相在低温丙烷氧化方面的催化活性。结果表明,只有(√5×√5)R27°-PdO可以在接近室温条件下催化丙烷氧化,而(√5×√5)R27°-PdO出现了大量氧缺陷,且形成还原的(2×2)-O相。程序升温脱附谱测到了完全氧化产物H_(2)O和CO_(2),在285和315 K出现两个主要反应温区。(2×2)-O和(5×5)-PdO相则无明显的催化活性。(√5×√5)R27°-PdO相的优异氧化活性可能与(√5×√5)R27°-PdO结构中较高的O密度相关,即结构中较活泼的O物种。本研究表明(√5×√5)R27°-PdO为丙烷低温氧化中的活性相。这些有助于人们理解三效催化剂的工作机制,对于高效低温三效催化剂的研发具有重要意义。Palladium,a key component of three-way catalysts used in automobile exhaust treatment,plays a pivotal role in complete oxidation of alkanes and low-temperature oxidation of CO.Under oxygen-rich conditions,a thin oxide layer spontaneously forms on the palladium surface.To understand the influence of the oxidized palladium surface on the active phase of low-temperature hydrocarbon oxidation,we have conducted a comprehensive study of the oxidation process on Pd(100)and its impact on propane oxidation.Our experimental results reveal that under varying oxidation conditions,the Pd(100)surface sequentially forms three different monolayered oxide phases,namely,(2×2)-O,(5×5)-PdO and(√5×√5)R27°-PdO.The oxygen coverage correspondingly increases in the order of 0.25 monolayer,0.56 monolayer and 0.8 monolayer.Notably,(5×5)-PdO is identified for the first time by high-resolution scanning tunneling microscopy.Experiments show this structure exhibits typical chiral features with its two enantiomers observed in the experiments.The chiral features of the(5×5)-PdO structure may bear significant implications in practical applications like chiral catalysis.Based on high-resolution atomic imaging,we have proposed a new(5×5)-PdO structure model.In addition,it’s experimentally revealed that upon thermal treatments the(5×5)-PdO structure decomposes into the(√5×√5)R27°-PdO and the(2×2)-O structures,and the(√5×√5)R27°-PdO decomposes into the(2×2)-O structure as well.These results suggest that the thermal stability of these oxide phases is in the order of(2×2)-O>(√5×√5)R27°-PdO>(5×5)-PdO.We have also compared the catalytic activities of these three oxidation phases in low-temperature propane oxidation.The results show that only the(√5×√5)R27°-PdO could catalyze propane oxidation near room temperature.We have observed a significant number of oxygen defects in the(√5×√5)R27°-PdO,which also forms the reduced(2×2)-O phase.Both complete oxidation products H_(2)O and CO_(2) are detectable by temper

关 键 词：氧化钯 手性氧化物 丙烷低温氧化 扫描隧道显微镜 

分 类 号：O647[理学—物理化学]