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首页> 外文期刊>ACS catalysis >Uniform Pt/Pd Bimetallic Nanocrystals Demonstrate Platinum Effect on Palladium Methane Combustion Activity and Stability
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Uniform Pt/Pd Bimetallic Nanocrystals Demonstrate Platinum Effect on Palladium Methane Combustion Activity and Stability

机译：均匀的Pt / Pd双金属纳米晶体表明铂甲烷燃烧活性和稳定性的铂效果

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摘要

Bimetallic catalytic materials are in widespread use for numerous reactions, as the properties of a monometallic catalyst are often improved upon addition of a second metal. In studies with bimetallic catalysts, it remains challenging to establish clear structure-property relationships using traditional impregnation techniques, due to the presence of multiple coexisting active phases of different sizes, shapes, and compositions. In this work, a convenient approach to prepare small and uniform Pt/Pd bimetallic nanocrystals with tailorable composition is demonstrated, despite the metals being immiscible in the bulk. By depositing this set of controlled nanocrystals onto a high-surface-area alumina support, we systematically investigate the effect of adding platinum to palladium catalysts for methane combustion. At low temperatures and in the absence of steam, all bimetallic catalysts show activity nearly identical with that of Pt/Al2O3, with much lower rates in comparison to that of the Pd/Al2O3 sample. However, unlike Pd/Al2O3, which experiences severe low-temperature steam poisoning, all Pt/Pd bimetallic catalysts maintain combustion activity on exposure to excess steam. These features are due to the influence of Pt on the Pd oxidation state, which prevents the formation of a bulk-type PdO phase. Despite lower initial combustion rates, hydrothermal aging of the Pd-rich bimetallic catalyst induces segregation of a PdO phase in close contact to a Pd/Pt alloy phase, forming more active and highly stable sites for methane combustion. Overall, this work unambiguously clarifies the activity and stability attributes of Pt/Pd phases which often coexist in traditionally synthesized bimetallic catalysts and demonstrates how well-controlled bimetallic catalysts elucidate structure property relationships.
机译：双金属催化材料对于许多反应广泛使用，因为在加入第二金属时通常改善单金属催化剂的性质。在具有双金属催化剂的研究中，由于存在多种不同尺寸，形状和组合物的多个共存活性阶段，它仍然具有挑战性地建立了透明的结构性质关系。在这项工作中，尽管金属在体积中不混溶，但表明了一种方便的制备小型和均匀Pt / Pd双金属纳米晶体的方法，尽管在体积中不混溶。通过将该组控制的纳米晶体沉积在高度表面积的氧化铝载体上，我们系统地研究向甲烷燃烧中加入铂催化剂的钯催化剂的效果。在低温和在没有蒸汽的情况下，所有双金属催化剂都显示出与Pt / Al2O3的活性几乎相同，与Pd / Al2O3样品的速率相比具有更低的速率。然而，与经历严重的低温蒸汽中毒的Pd / Al2O3不同，所有PT / Pd双金属催化剂都会保持燃烧活性对过量蒸汽的暴露。这些特征是由于PT对PD氧化状态的影响，这可以防止形成散装型PDO相。尽管较低的燃烧速率较低，但PD富含双金属催化剂的水热老化诱导PD / Pt合金相密切接触的PDO相的偏析，形成更活跃且高度稳定的甲烷燃烧部位。总体而言，这项工作明确地阐明了Pt / Pd阶段的活性和稳定性，它们通常共存在传统上合成的双金属催化剂中并证明了控制的双金属催化剂均如何阐明结构性质关系。

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