Palladium oxidation leads to methane combustion activity: Effects of particle size and alloying with platinum
Palladium oxidation leads to methane combustion activity: Effects of particle size and alloying with platinum
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DOI：
10.1063/1.5126219
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发表时间：
2019-10-21
影响因子：
4.4
通讯作者：
Cargnello, Matteo
中科院分区：
文献类型：
--
作者：
Goodman, Emmett D.;Ye, Angela A.;Cargnello, Matteo
Pd基和Pt基催化剂由于其在排放控制催化中的广泛应用而被高度研究。然而，关于金属的活性相和氧化态的权利要求仍然各不相同。由于含有各种金属纳米颗粒尺寸和组成的这种材料的异质性，可能得出不同的结论，这些材料各自具有独特的氧化还原特征。在这项工作中，使用均匀的Pd催化剂，我们研究了颗粒尺寸和合金化对Pd基催化剂的氧化还原性能的影响，并显示了它们对甲烷燃烧活性的贡献，使用operando快速扩展X射线吸收精细结构测量。结果表明，对于所有研究的Pd尺寸（3 nm-16 nm），Pd氧化直接先于CH 4燃烧成CO2，表明Pd氧化是甲烷燃烧的先决步骤，并且氧化预处理显示出与还原预处理相同或更好的催化作用。结果，然后扩展到均匀的合金PtxPd 1-x纳米粒子，氧化预处理，以提高低温燃烧。在这些均匀的合金，我们观察到一个组合物依赖的效果与富铂合金氧化和还原预处理之间的最大差异。在富Pt合金中，我们最初观察到Pt的存在使Pd保持在较低活性的还原状态。然而，随着运行时间的延长，PdO最终在氧化燃烧条件下分离，导致活性缓慢增加。总的来说，在颗粒尺寸和合金组成，我们涉及增加的催化活性Pd氧化，从而揭示了以前的对比结果与这些催化剂的甲烷燃烧活性。由AIP Publishing授权出版。
Pd- and Pt-based catalysts are highly studied materials due to their widespread use in emissions control catalysis. However, claims continue to vary regarding the active phase and oxidation state of the metals. Different conclusions have likely been reached due to the heterogeneous nature of such materials containing various metal nanoparticle sizes and compositions, which may each possess unique redox features. In this work, using uniform nanocrystal catalysts, we study the effect of particle size and alloying on redox properties of Pd-based catalysts and show their contribution to methane combustion activity using operando quick extended x-ray absorption fine structure measurements. Results demonstrate that for all studied Pd sizes (3 nm-16 nm), Pd oxidation directly precedes CH4 combustion to CO2, suggesting Pd oxidation as a prerequisite step to methane combustion, and an oxidation pretreatment shows equal or better catalysis than a reduction pretreatment. Results are then extended to uniform alloyed PtxPd1-x nanoparticles, where oxidative pretreatments are shown to enhance low-temperature combustion. In these uniform alloys, we observe a composition-dependent effect with Pt-rich alloys showing the maximum difference between oxidative and reductive pretreatments. In Pt-rich alloys, we initially observe that the presence of Pt maintains Pd in a lower-activity reduced state. However, with time on stream, PdO eventually segregates under oxidizing combustion conditions, leading to a slowly increasing activity. Overall, across particle sizes and alloy compositions, we relate increased catalytic activity to Pd oxidation, thus shedding light on previous contrasting results related to the methane combustion activity of these catalysts. Published under license by AIP Publishing.