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Structural transitions and stabilization of palladium nanoparticles upon hydrogenation

机译：氢化后钯纳米颗粒的结构转变和稳定性

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摘要

Using an explicit empirical potential and a combination of Monte Carlo and molecular dynamics simulations, we investigate the energetic, thermal and dynamical stability of hydrogenated palladium nanoclusters containing a few hundred atoms. At zero temperature, icosahedral clusters favour tetrahedral absorption sites, while cubic clusters preferentially absorb at octahedral sites. As a consequence, icosahedra can absorb a larger quantity of hydrogen than cubic clusters. However, even a moderate amount of absorbed hydrogen is found to favour cubic structures. There are two distinct effects of temperature. First, thermal desorption of hydrogen atoms can take place spontaneously even at low temperatures. Second, hydrogen rich cubic particles undergo a structural transition toward icosahedra before melting occurs. A simplified diagram is proposed to account for the observed behaviour. Finally, the coalescence between two clusters is studied dynamically for several clusters at various temperatures, both in the gas phase and for particles embedded in a simple model solvent. The heat produced from coalescence results in the desorption of hydrogen molecules. This leads to a significant cooling of the nanoparticle, thereby contributing to its stabilization.
机译：使用显式的经验潜力，结合蒙特卡洛和分子动力学模拟，我们研究了包含数百个原子的氢化钯纳米簇的能量，热和动力学稳定性。在零温度下，二十面体簇倾向于吸收四面体，而立方簇则优先吸收八面体。结果，二十面体比立方团簇可以吸收更多的氢。然而，发现即使适量的吸收氢也有利于立方结构。温度有两个不同的影响。首先，即使在低温下，氢原子的热脱附也会自发发生。第二，富氢立方颗粒在发生熔化之前经历了向二十面体的结构转变。建议使用简化图说明观察到的行为。最后，针对气相中的多个簇以及在简单模型溶剂中嵌入的粒子，动态研究了两个簇在不同温度下的聚结。聚结产生的热量导致氢分子解吸。这导致纳米颗粒的显着冷却，从而有助于其稳定。

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